Flash devices for FGPA  - Page 1
Forum section: electronics / general

author: joniengr081
author_rank: Regular Contributor
timestamp: December 27, 2022, 05:13:54 pm
content: Hi,I am wondering about the Flash devices which are normally used with Xilinx ZYNQ FPGAs. I actually have no idea before about the types of Flash device that can be used with FPGA and I need to include one Flash in a custom design on which I am working. In simple words, what is the difference between QSPI Flash, NAND Flash and Nor Flash ? I would like to know their signal interface, speed and cost etc.I am not sure if QSPI is interface having four I/O lines and the types of RAM are either NAND Flash or NOR Flash. Can someone please comment on that please to make the concept clear. Thanks in advance.and finally what is this S25FL127S QSPI flash, is it NAND or NOR type of Flash ?

author: asmi
author_rank: Super Contributor
timestamp: December 27, 2022, 06:05:07 pm
content: I'm not really sure I understand the question, but here are a couple of links which will hopefully help:1.7 Series FPGAs Configuration User Guide (UG470)Explains in great details all configuration methods.2.Vivado Design Suite User Guide: Programming and Debugging (UG908) -> Configuration Memory Supportlist supported flash memory devices.In reality the vast majority of FPGA boards use QSPI flash for loading a bitstream, because it's cheap, it's easy, requires just a handful of pins, and can be made relatively fast if a flash device supports it (most more-or-less modern QSPI flash devices will have no problems supporting highest possible configuration interface speed). BPI can sometimes be found mostly on older FPGA boards which implement PCI Express Endpoint because there is a limit to how long an FPGA boot can take, and in the past BPI has been the faster configuration method. But nowadays QSPI flash has become fast enough that it's throughput is comparable to BPI while being much cheaper to implement (BPI requires A LOT of pins, and BPI flash is typically more expensive than QSPI flash), so for a new designs I'd recommend to stick to QSPI unless you know what are you doing (but if it were the case, we probably wouldn't see that question here).

author: SiliconWizard
author_rank: Super Contributor
timestamp: December 27, 2022, 06:12:44 pm
content: As for the S25FL127S, a quick search would have given you the answer. It's NOR flash. If that even matters.https://www.infineon.com/cms/en/product/memories/nor-flash/standard-spi-nor-flash/quad-spi-flash/s25fl127sabmfi100/

author: joniengr081
author_rank: Regular Contributor
timestamp: December 27, 2022, 07:09:14 pm
content: Please explain bit more. When we say QSPI Flash, has it to be either NAND or NOR internally in structure or QSPI Flash has nothing to do with NAND and NOR flash ?

author: berke
author_rank: Frequent Contributor
timestamp: December 27, 2022, 07:25:19 pm
content: QSPI specifies the interface, it is "just" SPI but with four data lines and still a single clock. It is commonly used with but not specific to non-volatile memory chips. When talking about flash, it implies a command set as well. There are NAND as well as NOR flash devices using QSPI, random example Alliance AS5F31G04SND-08LIN is a NAND flash that does QSPI (as well as double and single bit SPI). I don't know if and how the NOR/NAD nature reflects in the command set.Wikipedia tells me that NAND flash is denser but less reliable and needs to be used with ECC (which may or may not be provided by the chip itself), while NOR is less dense but is expected to have sufficient reliability by design to be used as a firmware/logic configuration source.

author: joniengr081
author_rank: Regular Contributor
timestamp: December 27, 2022, 08:40:51 pm
content: Thank you very much for your reply and answering to my question.