Confused about Flash

John Larkin · 2006-11-03T23:46:26+00:00

One of my engineers left to go Indonesia and teach, or something, andI have inherited 17,000 lines of really ghastly, buggy, ugly assemblycode for an embedded product. It looks easier to rewrite it fromscratch than to try to fix it, so that keeps me off the streets forthe rest of the month.This thing has an ST flash chip, M29W400BB, which is 4M bits, used in256kx16 mode. The datasheet is typically confusing. So please check meon this:If I write a secret combination of words to a secret list of addressesin the chip, six writes total, I can tell it to erase one of its 11sub-blocks of memory. Apparently I can't do normal reads during erase,so I can't run the code out of the same flash I'm erasing. I have toerase a block (to all 1's, like an eprom) before I can program it. Ablock erase can take up to 6 seconds, but I can poll it to see whenit's done. Apparently I select which block is to be erased by writing0x30 into any address of that block, as the last operation of theerase command.(The datasheet is cute. I's not obvious whether writing to address"BA" means "write to address 0xBA" or "write to an address in theblock". Seems like the latter makes sense.)Write 0xAA to 0x555 0x55 to 0x2AA 0x80 to 0x555 0xAA to 0x555 0x55 to 0x2AA 0x30 to any address in block to be erased wait 6 secs or poll for erase doneProgramming flash is less clear. Apparently I execute a chunk ofsecret writes, one for each word I want to load, each with threecommand code writes followed by an address+data word write. "The finalwrite operation... starts the write state machine." I assume from thisthat the actual burn of a single word begins after eachpoke-a-write-word command sequence, and it seems to take 10 us typ,200 us max, and is again pollable for done. Write 0xAA to 0x555 0x55 to 0x2AA 0xA0 to 0X555 data to target addresswait 200 usec or poll for write doneIt sounds like here, once I erase a whole block, I can program anyaddresses within that block, as...

Nov 03, 2006 22 Replies

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Jim Thompson 19 years ago

A "thumb guide"... I'll let you fill in the rest ;-)

...Jim Thompson

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Ben Jackson 19 years ago

I gotta get me some of this action. Is your standard rate $1300/LED?

-- Ben Jackson AD7GD

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John Larkin 19 years ago

Well, there's some analog electronics, a uP, and an FPGA or two, usually. Sometimes only 2 led's.

We run about 22% parts cost overall. Given that "direct cost" is defined as parts+direct manufacturing+test cost, a bad product runs

3:1 selling price/dc, and a good one runs 6 or 8.

John

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