[sdiy] Digital delay memory

rsdio at audiobanshee.com rsdio at audiobanshee.com
Thu Apr 28 03:00:33 CEST 2016


On Apr 27, 2016, at 4:19 PM, Eric Brombaugh <ebrombaugh1 at cox.net> wrote:
> On 04/27/2016 03:44 PM, rsdio at audiobanshee.com wrote:
>> I'm sure there are ARM processors other than ST Micro that support SDRAM. I sure hope so, because I'm currently finding silicon bugs in the STM32F429 with respect to the external memory support.
> 
> Interesting. Care to elaborate on that? Are there workarounds?

It's been a long journey that isn't over yet.

At first, I was working with the rev1 STM32F429. I'm not quite sure why the distributor had dozens of these old parts in their inventory when the current documentation says rev3. I made the mistake of not reading the errata for the chip right away, and instead found some bugs the hard way. Once it was discovered that the errata explained most of the problems, and the chips were confirmed as rev1, many phone calls were needed to obtain rev3 STM32F429 parts.

Unfortunately, some other, similar issues still exist with rev3. Hardware revisions may be necessary to correct the timing issues, because the STM32F4xx FMC (Flexible Memory Controller) does not allow control of the Data Hold Time (only Address Hold Time, and Setup Time for Data and Address), making it necessary to stretch the data hold time with hardware latches.

By the way, I'm working on hardware that uses the FMC for both 24-bit SRAM and 16-bit SDRAM. The problem is that copying 32-bit data from SDRAM to SRAM ends up causing data errors when both external memory modes are used in rapid alternating accesses. The errata explains most of this, and the remaining issues might be all data hold time rather than FMC errors.

In any event, my next ARM will not be STM32F. I hope to use something else without the long errata list or backlog of buggy inventory.

Brian



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