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Published: Wednesday, 01 September 2021 18:59

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Flash Memory:

flash Memory is non volatile memory used to store data. In contrast to SRAM and DRAM memory which are volatile (lose data when powered off), flash memory retain data. Examples would be your USB Memory stick, SD memory card, SSD, etc. Note, Hard drive (HDD) stored data using different mechanism by using magentics (similar to CD/DVD technology). These are going out of phase and not worth pursuing anymore. Flash memory have virtually replaced these.

The only problem with Flash memory is that their wrt speeds are slow, as they have to use elevated voltage to program the bits of memory.

There are 2 kinds of flash: NAND type and NOR type. NAND is the one that is getting more popular.

NAND Flash Memory:

An intro paper on Nand memory:

https://www.longdom.org/open-access/nand-flash-memory-organization-and-operations-2165-7866-1000139.pdf

There is an organization called "open nand flash interface" (ONFI), which provides spec for Nand Flash i/f as to what pins they should have, speeds supported, cmds, reg, etc. All Nand flash manufacturers adhere to this spec, as they are all part of this org. Big companies which are members of this org include Intel, Micron, Hynix, etc. ONFi spec started from version 1.0 in 2007, and is currently at version 5.0

this is their spec link for different ONFI versions: http://www.onfi.org/specifications

ONFI 4.1 spec is what most manufacturers have their Flash chips based on, that is what we'll refer to: https://media-www.micron.com/-/media/client/onfi/specs/onfi_4_1_gold.pdf

Data interface types: ONFI 4 spec supports four different data interface types. These 4 i/f are supported on the same chip for backward compatibility. Early Flash memory chips supported SDR, and then grdually started supporting DDR with faster and faster speeds. SDR refers to single data rate where data is transferred on only 1 edge of clk, while DDR refers to dual data rate where data is transferred on both edges of clk each cycle. So DDR data throughput is doubled compared to SDR. The 4 Data interface types are:

1. SDR,
2. NV-DDR,
3. NV-DDR2
4. NV-DDR3. 

They have different speed, timing, voltages, etc. Details are in ONFI doc.

These are some of the aspects of different data interface:

Nand reliability:

There are many noise sources in flash Mem that can flip the state of a bit. There are many techniques employed to improve the reliability of Nand flash. Some of these are:

1. ECC (Error correcting code): ECC is used heavily to correct these errors. There's a large area devoted to ECC.

2. Write leveling: Bitcells wear out after a certain number of writes. So, write leveling is done so that bits which are being less written are spread around so that they are written more.

3. Many other misc techniques.

Basics of Nand Flash:

Target: A device contains 1 or more targets, where each target is controlled by 1 CE_n (chip Enable) signal. 

LUN (Logical Unit): A target is organized into one or more Logical unit called LUN. A logical unit (LUN) is the minimum unit that can independently execute commands and report status.  Specifically, separate LUNs may operate on arbitrary command sequences in parallel. A LUN contains at least one page register and a Flash array. The Flash array contains a number of blocks. Each block contains a number of pages.

Page: Unlike most memory technologies, NAND flash is ordered in pages which are written and read as a unit. The elementary unit of operation for a NAND Flash device is one page of data with control commands of the whole block (multiple pages). Therefore data can be written only to one page at once. As shown in Figure 5, a page is defined as cells linked with the same word line. This is the smallest programmable unit physically made up of a row of cells.  A page is the smallest addressable unit for read and program operations. Erase takes place on a block basis. The page size is typically 2 or 4 Kbytes,

Block: As explained above, a group of pages is called a block. A block typically contains of 32 or 64 pages (has to be a power of 2). A block is the smallest erasable unit of storage. The reason for this is that all the NAND strings  share  the  same  group  of word lines that are erased together.  

Plane: The  NAND  Flash  memory  is  composed  of  the  blocks  of  pages,  which  could  be  grouped  into  a  flash  plane.  Depending  on  the  kind  of  device,  planes  are  in  principal  mutually  independent.  A  single  plane  covers  local  buffering  for read and program data, and can process operations in parallel.

Nand operations:

NAND flash devices carry out three basic operations of rd, wrt and erase.

1. program a page: During  the  page  program  operation,  a  page  is  written  into  the  data  register  and  then  programmed  into  the  memory  array.  First  the  page  address  and  the  command  word  are  moved  into  the  device  followed  by  the  programming  data.  
2. erase a block: Flash  memory  allows  only  two  states:  erased  and  non-erased.  A  given bit of data can only be written when the media is in an erase state. When data is written into, the bit is considered dirty and unusable for other write operations. A write operation in any type of flash device can only be accomplished on an erased unit and so a write operation must be preceded by an erase operation. In the erase state, a byte can be either all zeroes or all ones depending on the kind of flash device.
3. read a page:Bits  in  a  flash  cell  are  read  by  changing  the  voltages  on  rows  and  columns  of  cells  followed  by  assessing  the  results.  In  a  page  read  operation, a page is moved from memory into the output data register.
   
   

These operations shown above are carried out in steps. In general, these are the steps:

1. 1st step, cmd is sent out on Data lines,
2. 2nd step. then row/col addr are sent out on data lines, Row addr is used to address pages, blocks, and LUNs. The column address is used to access bytes or words within a page, i.e. the column address is the byte/word offset into the page. Some op like "block Erase" require only col addr, so only 1 cycle addr issued. But some ops require both row and col addr, so 2 cycles needed with col addr issued in 1st cycle and row addr in 2nd cycle.
3. 3rd step. Finally,  the value to be read or written is put on data lines. 

NOTE: In a NAND Flash device read and program operations take place on a page basis rather than on a byte or word basis like NOR Flash. This dictates the need to have the size of data I/O register equal to the page size.

NAND Flash memory is controlled using set of commands, these sets  of  commands  differ  from  memory  to  memory.  There  are  many  commands,  some  are  universal  to  all  NAND  Flash  manufacturers  while some commands are manufacture specific and supported only by a  few  devices.  According  to  the  Open  NAND  Flash  Interface  (ONFI)  Standard there is a list of the basic mandatory command set. The most common  commands  are   ́program ́,   ́read  data ́,   ́erase ́,   ́reset ́, etc.

Timing diagrams: Attach hand written notes

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Published: Thursday, 26 August 2021 13:30

Hits: 1887

Dental List:

You can buy a lot of dental items for almost free, as there's always deals abounding.

ToothPaste:

Walgreens has deals on Toothpaste almost every month now (since 2021), where they have these on sale for free after rewards.

Dental Clinic: You almost always get free ToothPaste and ToothBrush from your dentist who you visit twice a year. Of course, the toothpaste are sample units, so they are small.

ToothPaste:

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Published: Saturday, 07 August 2021 21:51

Hits: 2890

cashback sites

Now comes the best kept secret, cashback sites. Whenever you shop online and buy something from an online store, the merchants pay out commission to whoever referred you to that site. So, if you used google search to find an item, and used the link from google search engine to go to that merchant's website, and bought $100 worth of item, than that merchant pays google anywhere from 1% to 20% of the sale to google as their commission. How does the merchant know about who referred you? Well, there is referrer id or something like that when you click on the link (in the url of the merchant), that says that this link came from google. Of course if you go on your own, then the merchant doesn't share the commission with anyone, nor do you get any reduction in price. So, merchant wins big in this case !!

It would have been nice if google or yahoo or some of these search engines shared some of the earned commission with you. Unfortunately they don't. Fortunately, there are other websites that share their commission with you. You can visit these websites whenever you shop online, and click on the merchant's websites from these cashback websites. These cashback websites end up giving 50% or more of their commission to the customer, which adds up over time.

These websites give you cash back anyhwhere from 1% to 20% of the purchase price. The only requirement is that you access the online merchant website through the link posted on these cashback (CB) websites, your cart must be empty at time of purchase and purchase should be completed within an hour or so. cashbackholic lists all the cashback websites for a given merchant, so you can use this website to decide which one is giving you the maximum cashback.

UPDATE 2025: Better than cashbackholic is cashbackmonitor as it shows historical cashback too => https://www.cashbackmonitor.com

Two of the popular and reliable CB websites are Ebates (aka rakuten)  and topcashback . These websites explicitly state how much CB you’ll be getting, along with the exclusions that apply. So use these for any merchant only after reading the fine print for exclusions. Many other websites do not list all their exclusions, but won’t pay you later because it was an excluded category as per their internal rules. Ebates and topcashback are very explicit in listing all their excluding, so if they haven’t excluded a category for cashback, means you will get cashback for it. I personally never had any issues with either of them. One other thing to note is that CB appears on your portal within 24 hours for both of these websites (for most of the merchants), so check the portal within 24 hours to make you got the CB. If you don't see the CB, then the purchase didn't track correctly (happens in < 5% of the orders). In that case, cancel the order (if the order hasn't shipped), and place the order again. Some readers claim that if the order is very large (payout being > $50), then there's a risk with CB portals not giving you CB. I never had that issue with either ebates or TCB, even with larger orders. Some bank offers don't track properly, but if you provide your bank statements verifying your bank opening and meeting required conditions, then they credit you in almost all cases.

CAUTION: Some travel websites change their prices when going thru a cashback portal, so definitely check prices of merchants both with and without going thru cashback portal. Has never happened with any other merchant except these travel sites.

Some more individual details about the CB sites:

• Rakuten (www.rakuten.com): Previously this website was called ebates. Rakuten bought ebates, and became a cashback website. If you sign up with them, they give you a bonus. Better yet, if you were referred by someone they give both of you a signup bonus. They offer up to $40 (as of 2025, it's upped to $50) in signup bonus to each of you, at least couple of times a year. I would suggest you wait for that signup bonus to come, and then sign up using a referrer. If you don't find any, I can refer you, and collect my $40 sign up bonus. You'll also get $40 signup bonus. But before any of us can get paid, you will need to spend at least $40 or so in purchases. Read the fine print.
  • Referrals: Use this link only when you can find an offer which is better via a referral link than one w/o it.
    • My referral link => www.rakuten.com/r/KAILAS79
    • www.rakuten.com/r/KAILAS79?eeid=28187 www.rakuten.com/r/KAILAS79
  • Meeting spending requirement: Rakuten only requires you to spend certain amount of money towards the purchase, irrespective of how much cashback you get (cashback can't be $0 though). If you don't have any purchase planned in next 3 months after you signup, then as a last resort, you can purchase GC from giftcards.com, using the link on rakuten. Over there, store branded GC cost $0 in fees, but Visa/MC cost $5-$6 in fees. Just purchase $50 in GC, and you will be on the way to get your CB (basically making the GC free). Or still you don't know what to buy, then buy $50 of "giftcards.com egift" card which allows you to use this egiftcard to buy any other GC on their website later (excludes Visa/MC cards). So, there's nothing to lose. I would wait for close to expiry of 3 months, before I buy from giftcards.com, as you may already make a real purchase before then from some other store.
    • Link => search for giftcards.com, or use this link => https://www.rakuten.com/shop/giftcards?
  • UPDATES for Signup promo: Check the details of offer below as offer changes every day. You don't want to signup with an avg offer.
    • 09/12/2025: $50  referral offer for both (highest ever offer). Valid from 09/10/2025 - 09/30/2025 => https://www.doctorofcredit.com/rakuten-50-5000-referral-bonus-highest-ever/
    • 04/23/2025: $40 referral offer for both (back again) => https://www.doctorofcredit.com/rakuten-ebates-refer-a-friend-you-both-get-a-40-4000-membership-rewards-bonus/
    • 11/20/2023: $40 referral offer for both => https://www.doctorofcredit.com/rakuten-ebates-refer-a-friend-you-both-get-a-40-4000-membership-rewards-bonus/

• TopCashback (www.topcashback.com): This is again one of the very reliable cashback site. There's also a signup bonus of $25 (varies from time to time, and depnding on ongoing promotions)if you use a referrer. Both you and your referrer get this bonus ($50 total in bonus amongst 2 of you). If you don't use a referrer, then you get $10 or $15 (their usual promotions). So, better to use a referral. But before anyone can get paid, you will need to have at least $10 in cashback rewards (NOT in purchases). You will most likely need to spend about $100-$200 in purchases before you or I can see that sign on bonus. Read the fine print.
  • Referrals:
    1. My referral link is: https://www.topcashback.com/ref/member31043961639
    2. Use above link to open account if you don't find any referrer on your own who can pay you more money. I'll pay you any referral bonus that I get over $30. So, if I get $40 in bonus, I'll pay you $10. If I get $30 in referral bonus, I pay you nothing.
  • UPDATES for Signup promo:
    
    1. 2025(May 16): Best offer of $50 is back. Link => https://www.doctorofcredit.com/topcashback-refer-friend-get-50-new-member-gets-0-2/
    2. 2024 (Sep 15): Best offer of $50 is back. Link => https://www.topcashback.com/account/refer-a-friend/
    3. 2024 (May): Best offer of $50 is back. Only the referrer gets $50, referred person gets nothing. The person referred needs to earn $10 in cashback before the referrer gets paid $50.
       1. Link => https://www.doctorofcredit.com/topcashback-refer-friend-get-50-new-member-gets-0/
    4. 2024 (Mar): $35 bonus directly to the person opening the account. No referral needed. Just use the link below by DoC.
       • Link => https://www.doctorofcredit.com/join-topcashback-get-a-35-sign-up-bonus-highest-ever-3/
    5. 2022 (June): $30  bonus for referrer and $5 bonus for person referred. Inferior as referred people can get $10 sign up bonus on their own.
    6. 2021 (Dec): $25  bonus for referrer and $20 bonus for person referred. Pretty close to the best offer of $50 combined being offered in the past
  • Bonus offers: TCB offers top up bonuses at least once a month. During Thanksgiving/Christmas, it's almost every week. See the section below on TCB offers for more details. You will see $2.50 pop up bonus almost every month on making a purchase of $10 or more (As of 2023, it's usually $2.50 bonus on $15+ purchase). During Thanksgiving/Christmas, they offer up to $4 on $15+ purchase. Instead of making a regular purchase, you can buy TCB Giftcards for 100's of stores (including walmart, ebay, etc) to meet the $15 requirement. You get some cashback, as well as the bonus. This way you don't have to worry about what to buy whenever these offers come up.
  • Some of the best sites for CB on TCB are as shown below (which usually allow GC to be used, and still pay cashback)
    
    1. www.walgreens.com: Buy anything from Walgreens and you get cashback of 6% on almost everything. They have good offers going on where you get a lot of items for free after WCR, so CB is extra free money.

    2.  www.groupon.com: Again, you get a hefty 10% CB here for any local deals. Usually, you can buy any local restaurant deal or local hair cut, oil change etc. If you can't find anything, buy $25 Krispy Kreme GC which go for $20, on top of 10% CB. You can pay with Groupon Bucks and still get CB.

    3.  www.homedepot.com: Buy anything from here as they give about 10% CB on a lot of stuff (furniture, decor, etc). They have very good return policy on everything (30 days for almost anything), so you are not stuck like other furniture stores.

    4. www.lowes.com: lowes also has 1% or more cb on almost everything. However, I've seen some orders where no cashback was allotted, even though the item was eligible for cashback. So, Lowes is little risky on how the cb is tracked. Even though I've paid with GC in many cases, TCB has given me cashback on Lowes purchases.

    5.  www.ebay.com: Here also, you get CB on almost everything (except regular cash like items as bullions, coins, GC, etc). I've always gotten every CB from ebay. ebay is good site for buying cheap items, mostly electronic parts for projects or toys for kids. Just keep things in your cart on ebay, until you get this offer. Then you go ahead ad buy. ebay is your safest bet, as TCB gives cashback on redemption of ebay GC too. 

       • UPDATE 2025: aliexpress and Temu are better than ebay, as you get a lot more CB, and items are cheaper too on these sites compared to ebay.
•  Slickdeals (www.slickdeals.net): This is primarily a deal website, but have gotten into cashback lately. It doesn't have a good tracking mechanism, and you will need to download their extension and install it, which is not something that I would advocate. However, from time to time they do have good cashback for some of the merchants. Particularly, for Macy's they sometimes have $10 cashback on $25+ purchase, which is pretty awesome (40% max cashback). Their rewards portal to sign up is: https://loyalty.slickdeals.net. NOTE: this rewards account is separate from their slickdeals account, though they both have the same login and password. Here you will see details of any CB earned. As I said, tracking is not good as of 2021, so email them if you don't see your CB in 10-15 days. They have offered $5 Target GC in past for installing their extension, not sure what their current offer is (probably none).

• Swagbucks/Mypoints (www.swagbucks.com, www.mypoints.com, www.inboxdollars.com): The parent company of all of these companies listed is Prodege LLC, which is a marketing and consumer insight company. swagbucks (SB), mypoints (MP), inboxdollars, upromise, etc are multiple cashback websites owned by Prodege. SB, MP are primarily websites for making money by offering your time to do activities, like watching ads, doing surveys, buying promotional items, etc. They also have cashback when you buy items from 3rd party websites linked on their portal. Both SB and MP are almost same, except that SB is the biggest brand and may be more reliable, but I've found all of these to be very unreliable. Sometimes, MP or other prodege sites will have a better offer than SB, so in those case, you can use MP, etc too. When I say SB below, the info applies to all of the prodege sites. I've recently started using them for cashback whenever their cashback rate is higher than other CB sites mentioned above. Their cashback is unreliable. If you check under activity->visited, and if you see a "pending" icon, you'll get cashback. If not, then you get paid nothing. I've used them occasionally when they have extra reward like $5 in swagbucks on making a purchase, or when I'm planning to use a gift card for a purchase (TCB and Rakuten never pay out cashback anymore on paying with Giftcards on most websites, while swagbucks still does as of Oct 2023. I've paid using GC on HomeDepot and Lowes and got CB all the time. Not sure how long that will last). I prefer to use other CB sits over SB, as SB doesn't have any customer service or it takes for ever if you have to resolve anything. I primarily use them for opening bank accounts, brokerage accounts, or buying things that are a money maker. They pay you in their own currency called "swagbucks". That can be redeemed for 1 cent per swagbuck. Or you redeem it for 10% more once a month for no more than $25. So, every month, you can get a $25 virtual Visa gift card for $22.50. Swagbucks is totally legitimate website, and I've gotten decent cash from them.
  
  • UPDATE 2025: SB/MP etc are NOT reliable for any big bank offers, or even CB offers on websites, especially if the bonus is big. I haven't gotten last few bonuses, and going thru customer service even after providing the proof is wastage of time, as they will NOT pay. You will have to file a BBB complaint. Sometimes they will pay you.
    • BBB link => https://www.bbb.org/us/ca/west-hollywood/profile/internet-service/prodege-llc-1216-100088742.
    • They also have a link on BBB to contact prodege directly. Try this too => https://prodegesupport.zendesk.com/hc/en-us/requests/new?ticket_form_id=360001971531
  • REFERRAL LINK: If you open an account by using my referral link below, we both get $3 in free money (i.e 300 SB), when you earn at least 300 SB in first 30 days. So, use the link below to open an account only when you have an offer going on that you are interested in. Referral link: https://www.swagbucks.com/p/register?rb=20277812
  • One other risk with swagbucks/mypoints, etc is that they may deactivate or block your account at any time for no reason, and there's no way you can get it unblocked. I haven't found a way to contact them once your account is blocked. You may use the link that shows on "contact". It sends them an email, but you can't put your own comments, and you will probably never hear back from them. So, all your money in swagbucks/mypoints is gone. So, it may be safe to just cash out everything at any point in time, and not go for extra 10% in rewards. You may lose all of it in case your account gets blocked. SB/MP may block you for any reason as uploading receipts, doing surveys, cashing out GC, email addr/name not matching with what you have with 3rd party merchant when shopping thru them, contacting customer service for missing payout, etc. There are 1000's of complaints about Prodege LLC, and most of them are account getting abruptly shutdown, just before the big cashout. They give big bucks, but also take it all way in a second. All said, all prodege sites are very risky, and you should always take out all your money as soon as they are paid (which is usually 31-45 days). I've gotten burnt with prodege websites, and I use them with caution (my accounts got blocked and i wasted a lot of time with no result). CB with them is always a hit or miss.
    • Link on how to prevent your prodege a/c from getting deactivated/blocked => https://www.doctorofcredit.com/ensure-new-swagbucks-topcashback-account-doesnt-get-deactivated-tips/

• CapitalOne shopping (www.capitaloneshopping.com): I myself have never used it, but people on DoC have gotten insane cashback for some of the offers. It's a shopping portal with CB similar to other portals above. You don't need their credit card or anything else in order t use their CB portal. They have varying on the same same product depending on whether you access them via website, mobile, or via browser extension. They pay out in points which may be redeemed for GC. More details => https://upgradedpoints.com/credit-cards/capital-one-shopping/

There are many other CB sites besides these, but I wouldn't trust them. I've gotten burnt in past, where they paid out nothing, and there's nothing you can do. So, my suggestion is to go with these 3 listed above (TCB, SD, Raketen), even if they offer you a lower CB. At least you will get something. SD is risky too, as there's no way for you to track visits. I never had any issue with TCB or Rakuten.

Current Deals:

Topcashback: Multiple cash back offers throughout the year

There are multiple offers from Topcashback thru out the year. Most common one is $2.50 on $10+ $15+ purchase (as of 2023, it's on $15+). Usually once a month. They usually have one on Fridays, lasting till Sunday. Sometimes they have higher cashback offers,which are only for a day. So, easy $30-$50 a year just for being a TCB member. Details here:

Offer (gets updated with latest offers):

• Link =>  https://www.doctorofcredit.com/topcashback-get-3-bonus-when-you-spend-10-today-only/

Buy TCB GC (qualifies for bonus): https://www.topcashback.com/topcashback-gift-cards/ (search for Topcashback Giftcard) to look for this merchant. TCB is the merchant itself for these GC. Buy Walmart which is as good as cash (Since you can use walmart GC to buy silver, gold, etc). Another good option is to buy Walgreens GC as you get 1.5% CB and you can use these to pay for your prescriptions. You can use paypal to pay too, which can give you 5% CB if uour credit cards gives extra cash back on paypal.

Deals:

• 10/31/25 => $10 CB on $200+ purchase. Valid 1 day only (buy Walmart or walgreens GC to get 5% CB)
• 09/18/25 => $2.50 on $15+ purchase. Expires 09/20/25 (6AM), so effectively only until 09/19/25 late night.
• 01/07/25 => $2.50 on $15+ purchase. Expires 01/09/25
• 11/08/24 => $3 on $20+ purchase. Valid 1 day only
• 09/17/24 => $2.50 on $15+ purchase. Valid 09/17/24 - 09/19/24
• 02/14/24 => $2.50 on $15+ purchase. Valid 1 day only
• 01/30/24 => $2.50 on $15+ purchase. Valid 1 day only
• 01/18/24 => $2.50 on $15+ purchase. Valid 1 day only
• 12/05/23 => $2.50 on $10+ purchase. Valid for 2 days => expires 12/06/23
• 11/10/23 => $2.50 on $15+ purchase. Valid one day only
• 11/03/23 => $4 on $15+ purchase. Valid one day only
• 01/27/23 => $2.50 on $10+ purchase. Valid 01/27/23 - 01/29/23

2022:

06/14/2022: Topcashback $2.50 cashback on $10+ purchase => expires 06/17/2022

https://www.doctorofcredit.com/topcashback-get-3-bonus-when-you-spend-10-today-only/

01/25/2022: Topcashback $2.50 cashback on $10+ purchase => expires 01/27/2022

https://www.doctorofcredit.com/topcashback-get-3-bonus-when-you-spend-10-today-only/

2021:

11/16/2021: Slickdeals $10 cashback on $25+ Macy's online purchase => expires 11/16/2021

https://slickdeals.net/f/15405685-slickdeals-cashback-at-macy-s-pc-req-d-10-cashback-on-25-orders-free-s-h-on-25-orders-or-free-store-pickup-on-qualifying-items

You get $10 in slickdeals rewards on $25+ purchase. You need to install slickdeals extension though. Limit is 3 purchases per account, need to make separate purchases to get $10 on each order.

10/15/2021: Topcashback mystery offer every Friday until Thanksgiving - $2.50 cb on $10+ purchase => expires 11/29/2021

UPDATE 11/23/2021: Topcashback has $5 CB on $10+ purchase for 11/23-11/24. This is on top of Friday offers that have been for $2.50-$3.50 on $10+ purchase.

If you are planning to make any purchase, it's best to wait until Friday of that week. TCB is iffering mystery offer (usually $2 to $4) on $10+ purchase to any website which gives you cashback for that item. You have to activate the offer, by finding that offer. If you don't activate the offer prior to your purchase, you don't get the extra bonus CB. Walmart and Amazon rarely have cashback on anything of use, so don't use these sites to buy anything. Instead use below sites which don't have any exclusion on any items purchased from that site (except for few items listed specifically on the site, also don't pay with GC as some the sites exclude items bought with GC).

Few links with current offers:

https://www.doctorofcredit.com/topcashback-spend-10-get-4-bonus-cash-back-friday-only-11-5/

https://www.doctorofcredit.com/topcashback-spend-10-get-4-bonus-cash-back-friday-only-10-29/

https://www.doctorofcredit.com/topcashback-get-3-bonus-when-you-spend-10-today-only/

Few sample sites to use, which give you guaranteed CB

www.walgreens.com:

www.groupon.com:

www.homedepot.com: You can always buy something for in store pickup. I usually buy salt pallets for water softener.

www.lowes.com: This gives the lowest cashback, but may have something that you can do in store pickup

www.ebay.com: Use it to buy cheap items shipped from china

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Published: Tuesday, 20 July 2021 05:22

Hits: 4027

PT DSLG (define scaling lib group):

In previous section, we saw that PVT variations can be modeled by using derating on cells. Voltage and Temperature variations were modeled by using derating. Different derating values were applied to different cells depending on ir drop and temperature of the cell. We had 4 voltages that were applied depending on if the cell was on clock path or data path:

1. Early Clock Voltage (EC) => shortest delay path for clock (fast clk)
2. Early Data Voltage (ED) => shortest delay path for data (fast data)
3. Late Clock Voltage (LC)=> longest delay path for clock (slow clk)
4. Late Data Voltage (LD) => longest delay path for data (slow data)

Derates are inaccurate, and a lot of spice simulations have to be performed on different cells to figure out the value of derates for a given voltage drop. A lot of things are not accounted for when estimating derates, as it's very time consuming process. For ex, impact of voltage on drive strengths, input slews, output loads, pin caps, etc are not accounted for. We had to use derating, because we didn't have libraries for each and every voltage and temperature combination. However, if we did have continuous libraries for each and every voltage and temperature, then we could accurately calculate the delay of any cell, by figuring out it's voltage and temperature, and then calculating it's delay at that corner from the library. This would be much more accurate than the derate approach (process variations are still accounted for by using derating, it's only Voltage and Temp that we account for by using this method). This is known as the "scaling" methodology. This scaling flow from synopsys PT is called DSLG (define scaling lib group) flow.

There are 2 different techniques employed in DSLG:

1. Library scaling: Library scaling is a known technique that performs voltage and temperature scaling by interpolating data in libraries that was characterized at different voltage and temperature corners. This cross-library scaling
allows us to analyze timing, noise, and power at voltage and temperature values that are different from that of the corner libraries. CCS libraries are generally used for scaling as the scaling is more accurate. NLDM libraries may also be used, although accuracy will be lower.

For library scaling, following guidelines should be followed:

1. All libraries should be checked by using Library Compiler Qualification System to make sure libraries an be scaled. All lib need to have identical cell names, pins names and identical arcs.
2. Linking library that is provided via using "link_library" cmd (or using min_library to specify min lib too) is still provided and is used for linking the design. This link lib can be present in only one of the groups defined using "define_scaling_lib_group". Rest of the libs provided are used for scaling purpose only. In DSLG flow link_library has no special meaning (as all libs in a group have same arc, only the values of arcs change). link_library is used as a fallback library, when PT can't continue with DSLG flow.
3. 1D scaling requires atleast 2 libs. General 2D scaling requires at least 3 libs. Temp and Voltage are treated as separate scaling dimension. PT currently supports 3 different types of scaling formation => 2^n on the grid, (2n+1) and (n+1). For single voltage domain, it doesn't matter, but when we have multiple voltage domain on same cell (such as level shifters)l, then scaling is more complex.
4. Delay can usually be interpolated linearly. But for setup, hold, recovery, removal, min pulse width (MPW), min period (MP) constraints, etc., more accurate non linear interpolation is done. 
5. For single voltage design running in single mode, we don't need to specify PVT cond, as there's only 1 lib to use. We do provide op cond for PVT, but the values in there aren't used for anything.

Besides modeling voltage and temperature changes, scaling reduces the number of libraries required for the analysis of multivoltage designs and therefore reduces the library characterization effort. Usually only voltage scaling is done, and derating is still used to account for temperature variations. Since Temperature variation is much less (only +/- 15 degrees or so), and scaling is not very accurate for this (as temperature and delay don't follow a monotonic relation at low nm tech), we don't usually do temperature scaling.

PT cmd: define_scaling_lib_group <libs> => To define a library group for scaling. We use this cmd multiple times to define multiple library groups to cover different portions of the design. We need different groups for diff libs that contain diff kind of cells as svt, lvt, level shifter, special cells, hard IP, etc. We can't scale data from lvt to svt or vice versa. So, we can't have these in same group for scaling purpose. Moreover, each library can be part of only one library group.

pt_shell> define_scaling_lib_group {lib_0.9V_0C.db lib_1.05V_0C.db lib_1.3V_0C.db} => This creates a lib grp with 2 libraries used to scale data from 0.9V-1.3V. PT reports a messages as "completing scaling lib gropus, loading db files ... scaling complete". That means all libs were consistent and scaling could be performed. SLG-308 and SLG-318 errors indicate that some arcs in link lib aren't there is scaling libs, and scaling can't be done. These will need to be fixed or else flow will fall back to link_library for timing.


2. Exact matching: As an alternative to library scaling, we can use library data in an exact-matching flow, where operating conditions must exactly match one of the libraries. In this flow, PrimeTime chooses a matching library based on the operating conditions applied to the specific design cell instances. If no matching library is found, PrimeTime issues an error message (or SLG-216 warning) and does not perform scaling. This warning helps you detect mistakenly applied operating conditions. Exact matching is used in conjunction with scaling. We specify exact matching for memories, phy and other hard macros, which don't have well defined relationship with voltage and Temperature (also internal paths are hidden, so hard to say how do the interface paths scale). In this case, we just do a exact match

PT cmd: define_scaling_lib_group -exact_match_only <libs> => same cmd as above, except we need to add the option -exact_match_only"

pt_shell> define_scaling_lib_group -exact_match_only {lib_0.9V_0C.db lib_1.0V_0C.db lib_1.1V_0C.db} => Does exact match only. If no matching corner library is found, the tool issues SLG-216

3. Best matching: As an alternative to exact matching, we also have a best-matching flow. Here, closest lib is found (when an exact match is not avilable) and that lib is used for analysis. Syntax same as above (This option not yet available in PT docs as of 2020).

pt_shell> define_scaling_lib_group -best_match {....}


NOTE: There's an extra option "-exclude_rail_names" to ignore certain rails for scaling or matching purpose (for rails that are irrelevant for timing analysis on an IP. i.e SRAM voltage inside an IP, where SRAM paths are not exposed to IP pins, we can exclude SRAM voltage power rail for matching purpose). This option not yet available in PT docs as of 2020.

pt_shell> define_scaling_lib_group -best_match  -excluded_rail_names {  VBB VPP BIASNW VDD_SRAM ... } { lib1.db lib2.db ... }

Additionally, we can set this user attribute to tell the tool to not scale certain IP, etc:

pt_shell> set_user_attribute -quiet [get_lib_cells */IP_SRAM] is_scalable false

DSLG flow:

1. Read library: link library as before with one of the timing library. In DSLG flow, link_library is just a fallback library to use in case something goes wrong with "scaling lib", and DSLG flow is not run.

2A. Read netlist:

• Read verilog netlist: read_verilog ...
• Set DSLG libs: define_scaling_lib_group <libs> => link library above may be used at most in one these groups. When finished, it prints "scaling complete" message
• report_lib_groups -scaling -show {voltage temp process} > ~/dslg_grp.txt => Once lib groups are defined, we can report all scaling groups defined above , by using report_lib_groups cmd. It shows all groups along with the libs, their voltage+Temperature that we are using for that group. One of the groups is used for each cell in design. For seeing summarized info, just use "report_lib_groups -scaling". As an ex, o/p will show all SVT stdcells in diff voltage libs in one grp, all LVT cells in diff voltage libs in other group, each hardIP with diff voltage libs in another group and son. There may 10-100 of groups that it may show depending on how many groups were defined (which is dependednt on how many diff kind of lib cells were there).
  • sample o/p: group 1: tsmc_stdcell_svt_0p9v_m25c tsmc_stdcell_svt_1p1v_m25c group 2: tsmc_stdcell_lvt_0p9v_m25c tsmc_stdcell_lvt_1p1v_m25c and so on ...
• linking: link cmd not needed as above cmd does linking, if linking wasn't done already.
• list_libraries > ~/all_libs.txt => lists al libraries.. see detail of cmd in "PT Object access functions" section
• report_design => lists op cond. see detail of cmd in "PT-OCV" section

2B. Read parasitics file => Read spef file as before.

3A. Read constraints: Read all constraints as FP, MCP, SCA (set_case_analysis), etc.

3B. Setting Temp and Voltage: Here we have to set Voltage and Temperature for each cell in design. Previously we used set_operating_conditions cmd to set op_cond for the design. That specifies PVT for the whole design (either 1 set of PVT or 2 sets of PVT depending on analysis mode). For OCV flow where we needed to specify diff PVT for each cell, we specified diff derating for each cell in design. Here in DSLG flow, we use a combination of derating and scaling. First we set voltage and temperature for each cell using set_voltage and set_temperature cmds, and then account for process variations using derating:

• set_operating_conditions <WCCOM> => sets op cond. See in "PT - OCV" section for details
• set_voltage => defines voltage on pwr nets or pins. For pins, we specify the cell name and the power pins of that cell to apply the voltage. We can  specify all 4 kinds of voltage for a power net - early clk/data, late clk/data depending on whether the cell is on clk path or data path. By default voltages apply for both data and clk. If we want to specify a diff voltage for clk path, we need to use option "-clock". By default voltages apply for both early and late. If we want to specify a diff voltage for late, we need to use option "-min". min or max refers to path delay here, so min means min delay (i.e fastest case), while max means max delay (i.e slowest case). There's a -dynamic option that specifies portion of voltage change that varies with frequency (i.e ripple in voltage supply). Frequency o this ripple is several clk cycles. This dynamic portion is considered during capacitive coupling analysis and various pessimism removal optimizations. This option is not used generally.
  
  • syntax for least voltage applied to both data/clk paths: set_voltage <max_delay_voltage> -dynamic <dyn_max_delay_voltage> -object_list <list_of_power_nets> => These options are for max delay (i.e slowest path). Add -min option to specify voltage for min delay (i.e fastest path). Applies to both clk and data if -clock not specified.
    
    • ex: set_voltage 0.540 -object_list {VDD_SOFT VDD_ON} => Here 0.54V is specified on power net VDD_SOFT, VDD_ON for both clk/data and for both early/late paths
    • ex: set_voltage 0.540 -min 0.562 -object_list VDD_SOFT => Here 0.562V is applied on early path (both clk/data), and 0.54V on late paths (both clk/data).
    • ex: set_voltage -clock 0.540 -min 0.562 -object_list VDD_SOFT => Here max/min delays are applied only on clock path. For data path, max/min delays are applied if set_voltage used without "-clock" option.
  • We also have an option to set voltage directly on pg pin of a cell, if we want to override what's provided on power net.Here we use -cell option to specify cell list, and -pg_pin to specify each pg pin of cell.
    
    • ex: set_voltage 0.04 -min -0.05 -cell I1 -pg_pin_name GND => sets "GND" pin of cell "I1" to 0.04V and 0.05V
    • ex: set_voltage -pg_pin VDD_SRAM -cell [get_cells I_top/sram_cell] 0.75 => Here we are setting pg pin of sram directly with a voltage. NOTE: voltage value is specified at end of cmd, and not in middle.
  • The way to use "set_voltage" is to first read in UPF file (which specifies power domain and power connections). Then specify voltages on these power nets or on each instance power pin.
  • In case you don't have an UPF file, you will need a pg verilog netlist, which has power pin connections for each instance of cell. Then we can use set_voltage to specify voltages on these power nets or on each instance power pin.
  • NOTE: since voltage may not be set for each every cell in design, there is a voltage priority sequence that's followed in case of voltage setting conflicts or voltages not defined explicitly:
    • Firstly, default supply voltage set via "voltage_map" in liberty file is taken as voltage.
    • If set_operating_condition is used, then that is applied to the design.
    • Then if set_voltage is applied on supply net, then that takes priority over the previous two. However, if set_voltage is applied on PG pin of a cell, then that takes highest priority.
• set_temperature => It's the counterpart of set_voltage for setting temperature. We can specify min and max case temp for cells on the design, so that are timed and optimized at the specified temperature. min and max refer to min delay (best case) and max delay (worst case). Min/Max case are used for early and late paths.
  
  • syntax: set_temperature <max_case_temp> -min <min_case_temp> -object_list <list of cells>
    
    • ex: set_temperature 125 -object_list [get_cells "I1 I2"] => this specifies both min and max case temp on this cell to be 125C.
    • ex: set_temperature 125 -min 25 -object_list [get_cells "I1 I2"] =>here min_case (best_case) temp is 25, while max case (worst case) temp is 125 for both cells.
  • NOTE: most of the times, we don't use temperature scaling, so we just use derating numbers, and not use this cmd at all.
• check_timing: CMD => check_timing -override_defaults operating_conditions => Very imp to run this cmd. This operating cond check issues warnings as SLG* which need to be fixed. For scaling lib groups, it issues warnings if operating condition is set beyond the range of the libraries in the scaling group. For exact-matching library groups, issues a warning when operating conditions do not match any of the libraries in the scaling group For cells that are not part of either exact matching or scaling groups, it uses operating condition in link lib, and if different, it issues warnings.

4. Generate reports => generate timing reports and all other reports for analysis. NOTE: most of the lib reporting cmds that we used earlier, report link_lib when used in DSLG flow, when in reality the lib being used for timing are "combo of scaled libs" or "best matched lib" which may be different than "link_lib".

Additional helpful reports for DSLG:

• report_delay_calculation => This cmd shows how the tool scales data for delay calculation. When used with the -thresholds option, it also reports cell instance operating condition and rail names. For example:
  • pt_shell> report_delay_calculation -from [get_pins cell/A] -to [get_pins cell/Z] -thresholds => shows all rail voltages and op cond.
    
    • NOTE: it shows linking lib at the top of report, which is just some lib that was used for linking. Then below it, it does show all scaling libs being used, and those are the one from which it extracts the delay at the voltage needed. It will show the delays, but it won't at what voltage level those delays were calculated. To see voltage level on the cell, we need to use other cmds below.
• report_power_pin_info =>This is the most useful cmd to find out voltages on pg pins of any cell. It shows PG pin connections for that cells (i.e VDD pg pin connected to VVDD_CHIP, etc). It shows voltages all 4 possible voltages to be used depending on whether's it's on clk or data path => clock max/min delay, data min/max delay (early/late voltages that we talked above)
• report_power_net_info => Once power nets are assigned voltages, this cmd may be used to dump out op voltages for all power nets in design. Even though PT docs show this cmd, and "man report_power_net_info" shows info for this cmd, but it errors out with "unknown cmd" in PT 2021 versions.
• report_timing -voltage -derate => This is the best way to know supply voltage and derating being used for timing purposes on a cell is by running "report_timing" with option "-voltage" and option "-derate". If set_voltage cmd isn't used to set worst_case/best_case voltages, then derating numbers being used will be larger to account for voltage variations too (In this case, it uses same voltage for all paths, but uses derating to model for wc/bc voltage). Derating already accounts for process and Temp variations, with dslg it doesn't need to account for voltage variations.
  • setup timing: pt_shell> report_timing -thr top/cell_a -delay max -voltage -derate => Since this is max delay (setup), this will show min voltage on launch clk and data, and max voltage for capture clk (used for all cells in clk/data path).
    • launch clk path => LC (late clk). Lowest voltage applied accounting for off chip IR drop and on chip IR drop. We don't account for any voltage reliability drop for clk path, since clk path is always switching, so Vth degradation doesn't happen. This voltage is slightly higher than data path voltage, since voltage droop due to reliability isn't included here. ex: voltage applied may be 1.1V. For derate, it will show derate of >1, i.e 1.02 (i.e 2% slower path). NOTE: derates will be much higher if different voltages aren't applied to different paths. Here derates only model process and temp variations.
    • data path => LD (late data). Lowest voltage applied accounting for off chip IR drop, on chip IR drop and any voltage reliability drop (due to cells not switching all the time, Vth degrades). This voltage is slightly lower than voltage applied to launch clk path, as extra voltage reliability drop is accounted for here. This is the lowest voltage that chip can ever see. ex: voltage applied may be 1.0V. For derate, it will show derate of >1 but slightly more than derate in launch clk path, i.e 1.05.
    • capture clk path => EC (early clk). Highest voltage applied on this path accounting for only off chip IR drop. This is the highest voltage that chip can ever see. ex: voltage applied may be 1.2V. For derate, it will show derate of < 1, i.e 0.96 to indicate it's 4% faster
  • hold timing: pt_shell> report_timing -thr top/cell_a -delay min -voltage -derate => Since this is min delay (hold), this will show max voltage on launch clk and data, and min voltage for capture clk (used for all cells in clk/data path). Ex: Voltage shown may be 1.1V, which is higher than one shown above.
    • launch clk path => EC (early clk). Highest voltage applied on this path accounting for only off chip IR drop. This is the the same voltage/derate as on "capture clk path" in setup timing. ex: voltage applied may be 1.2V. For derate, it will show derate of < 1, i.e 0.96 to indicate it's 4% faster
    • data path => ED (early data). Highest voltage applied on this path accounting for only off chip IR drop. This is the same as the voltage on launch clk path. ex: voltage applied may be 1.2V. For derate, it will show derate of < 1, i.e 0.96 or same as for launch clk path. 
    • capture clk path => LC (late clk). Lowest voltage applied accounting for off chip IR drop and on chip IR drop (no voltage reliability drop). This is the same voltage as on "launch clk path" in setup timing. voltage applied may be 1.1V. For derate, it will show derate of > 1, i.e 1.02 or same as for launch clk path in setup timing. 

report_lib <lib_name> => Here we can check for op_cond defined in specified lib. Not very useful, as we can do that by manually looking into lib file. See detail of cmd in "PT Object access functions" section

report_cell <cell_instance_name> => this shows ref lib cell, OC used, voltages etc for given cell. In DSLG flow, OC cond shown are from This is very helpful cmd. see detail of cmd in "PT Object access functions" section

shows ref

ame as regulat PT flow until read_

More PT scaling related useful cmds:

1. report_lib_groups: Once lib groups are defined, we can report all scaling groups defined, by using report_lib_groups cmd.

pt_shell > report_lib_groups -scaling -show {voltage temp process} > ~/tmp1.txt => It shows all groups along with the libs, their voltage+Temperature that we are using for that group. One of the groups is used for each cell in design. For seeing summarized info, just use "report_lib_groups -scaling"

2. report_delay_calculation => command. The report shows the results using the link library, then the scaling library group results if applicable and valid.

set_voltage

set_operating_condition