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STM32F429 SDRAM unreliable

Question asked by mcconaghy.peter on Oct 20, 2014
Latest reply on Jan 26, 2015 by gregory.glen
I've copied the SDRAM hardware and software from the STM32F429 Discovery board. We've made a few boards so far. On some the SDRAM doesn't seem to work at all while on others it seems to work for a bit then get corrupted later on.

We're using it as a temporary RAM buffer for an LCD at the moment - the data is updated in the SDRAM then written out to the LCD via SPI. When the SDRAM works we get the expected screen. When it doesn't we get random garbage. Sometimes the whole screen is one colour (ie all the SDRAM has the same value). Sometimes as it goes down the screen it goes from black (0x0000) towards some colour (ie bits being set). Sometimes it contains random "snow".

As far as I can tell (I've checked a number of times) the hardware is wired up the same. I'm using the same SDRAM chip. I've copied the stm32f429i_discovery_sdram.c code from the firmware package. I'm using the same 8MHz crystal.

I tried changing the following settings but it made no difference (based on some other sample code)
  FMC_SDRAMCommandStructure.FMC_AutoRefreshNumber = 8;

I'm not sure where to start looking at it... help!