SPI SRAM - Page 1
Forum section: electronics / beginners

author: Tom Harker
author_rank: Newbie
timestamp: July 15, 2018, 04:50:39 pm
content: I need to store a reasonable amount of data and I'm trying (and failing) to find a chip with:-PDIP/SOIC package (I can solder these)-more than 4Mb of storage (storing short uncompressed audio clips)-SPI interface (for lower pin count and to match the rest of the data flow)-very high endurance read/write-not too expensive (FRAM!)I've found VTI7064MSME which fits the bill but it seems a bit dubious and I don't think it has a 'HOLD' pin (to avoid repeat address transmission).I'm aware there are flash storage chips but they have limited overwrite endurance and I'm trying to make something that will last.Can anyone help?Thanks

author: Benta
author_rank: Super Contributor
timestamp: July 15, 2018, 05:48:24 pm
content: Check ISSI. They have SPI SRAM in SO-8 up to 4 Mb. Good supplier with long life product support.No affiliation, but I've worked with them and was very satisfied.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 15, 2018, 05:55:46 pm
content: Just how much audio, in total, are you looking to store?Example, stereo 44.1kHz sample rate 16 bits, is 5.94 seconds. As a continuous circular buffer, a net-size Flash chip will last a week, assuming you need rated retention time. But needing only a 6 second retention time, you'd probably get the better part of a year, maybe several years of useful life, call it planned obsolescence with a graceful failure mechanism (i.e., the audio gradually corrupts with pops and hiss -- which would be a good idea to detect and mute).Huge Flash chips are readily available. You're literally paying as much, or more, for a small Flash chip, as for a gigabit one.If this is for brief snippets, forget about it, stuff it in Flash. Even if it's continuous buffering, use Flash.Otherwise, something like self refreshing DRAM (pseudo-SRAM). No idea if that's available in SPI flavor.Your PDIP/SOIC requirement is easily satisfied: get a micro-SD breakout board. Now you have oodles of gigabytes on an SPI header. You'll never run out!I don't get the lack of compression. Even on a $2 MCU, you have enough clock cycles to do at least a simple compression: mu-law scaling, Huffman encoding, various kinds of DCT, or fancier methods like SMASH or lzop or gzip. A combination of these will net you at least a very worthwhile 2x savings, or easily more than 16x if you allow some degradation in quality.Tim

author: Tom Harker
author_rank: Newbie
timestamp: July 15, 2018, 06:00:38 pm
content: Thanks, I've actually ordered some of these ISSI FBGA chips, at huge expense from mouser.com:https://www.mouser.co.uk/ProductDetail/870-WVH8M8ALL166B1LII don't think I'll get far with them given how tiny they are! I'm sure I've seen a 4Mb SOIC chip from them, but I can't find a place to order it

author: voltsandjolts
author_rank: Unknown
timestamp: July 15, 2018, 06:03:45 pm
content: Yeh, I vote for NOR FLASH or SDCARDe.g. 100K prog/erase cycles, SOIC8 - even the small 64Mbit can be wear levelled to give you at least 64Mb/4Mb= 16 * 100K = 1.6million prog/erase cycleshttp://www.cypress.com/file/316661/download

author: Tom Harker
author_rank: Newbie
timestamp: July 15, 2018, 06:07:25 pm
content: From my 'calculations' I'm looking at a max of 28 seconds of 16bit audio at 44100Hz mono, but two channels. So about 40 Mb. Micro SD makes my balls itch, I've burned up a few of those I'm sure. I'm trying to build something that will last 25 years, no particular reason other than some self-imposed standards. As for compression, and this is likely the wrong approach, it will be done in 'real time' so two bytes in, two bytes out - that doesn't really allow for compression as far as I understand it. Thanks for the ideas.

author: Benta
author_rank: Super Contributor
timestamp: July 15, 2018, 07:29:14 pm
content: Quote from: Tom Harker on July 15, 2018, 06:00:38 pmUm, you're linking to 8-bit wide HyperRAM, not SPI types.The SPI devices are called IS62WVS..... and are freely available up to 2 Mb in SO-8:https://www.mouser.co.uk/new/issi/issi-is62wvs-sram/4 Mb types were sampling 1Q2018 and should be mass-production now.http://www.issi.com/WW/pdf/Serial-SRAM.pdf

author: Tom Harker
author_rank: Newbie
timestamp: July 15, 2018, 07:54:54 pm
content: I'm aware that the chips I have bought aren't SPI, I'd sort of given up on finding anything, but then I remembered EEVBlog so thought I'd ask here. I've heard of ISSI 4Mb SOIC SRAM, but I can't find anywhere to buy it.

author: Benta
author_rank: Super Contributor
timestamp: July 15, 2018, 08:03:40 pm
content: The 4 Mb parts are in full production. You can order samples directly from ISSI.

author: tsman
author_rank: Frequent Contributor
timestamp: July 15, 2018, 08:05:46 pm
content: What are you trying to interface this RAM to anyway? No external memory bus available?

author: David Hess
author_rank: Super Contributor
timestamp: July 15, 2018, 08:14:45 pm
content: Quote from: Tom Harker on July 15, 2018, 06:07:25 pmSome form of ADPCM (adaptive differential pulse code modulation) may be suitable. At the very least, u-law or a-law compression could be used.http://www.drdobbs.com/database/algorithm-alley/184410326I see that 2Mbit SPI SRAMs in 8 pin packages are a reasonable cost but 40 Mbits of required storage is going to make that uneconomical leaving some form of Flash memory. I would lean toward either SPI NOR Flash or an SD or microSD card.

author: Tom Harker
author_rank: Newbie
timestamp: July 15, 2018, 08:23:08 pm
content: I'm planning on interfacing the SRAM with a micro-controller by SPI, possibly an ATMEGA16 because it has plenty of pins for chip select. I'm using SPI because it is simple and I'm using it elsewhere already.

author: Tom Harker
author_rank: Newbie
timestamp: July 15, 2018, 08:45:57 pm
content: I'm not familiar with ordering samples. How does this work? I assume they wouldn't just give away 10 RAM chips? There's a 'comments' input on the ISSI sample request form, what info do they need?

author: Benta
author_rank: Super Contributor
timestamp: July 15, 2018, 09:01:56 pm
content: Greenhorn, eh?Just say you're an engineer hired as consultant on a project for a major company. You're contractually not allowed to say more, except that it's to do with industrial control.You'll get your samples, but expect a phone call at some point.

author: Tom Harker
author_rank: Newbie
timestamp: July 15, 2018, 09:36:33 pm
content: I think I'm out of luck on this one, none of ISSI's suppliers have the part and it appears as 'no inventory' on their product list.

author: Benta
author_rank: Super Contributor
timestamp: July 15, 2018, 10:08:29 pm
content: What do you mean? ISSIisthe supplier. The other companies listed are distributors.Did you click "Sample & Buy" and then "Request Samples"?

author: Tom Harker
author_rank: Newbie
timestamp: July 16, 2018, 12:26:56 pm
content: I did, but I'm not too keen on putting together some lies about what I'm doing. Also, I'm concerned that the chip is listed on their site as having 'no inventory', I'm not sure what that means. Is it that they don't know how many they have in stock? What I might do for now is use the 2Mb version to get things designed and built, then switch to the 4Mb version when I can legitimately buy a reel from them. I'll figure something out. Thanks to everyone for your input, highly appreciated!