STM32H7 FMC and 16bits device

[Alex_J]

Hello,

I'm kind of newbie in the STM32 world, I'm more used with another brand of 32bits microcontroller that also have a "parrallel port" for interfacing external ram device.

My concern is about the FMC on the STM32H7.

I want to read/write a 16bits device.

Currently I'm using this configuration (almost the default one) :

My code for testing a write operation :

....

I can't see any problem in the code but when I check signals with an oscilloscope, I can see that the CPU is issuing 4 consecutive write operation :

A0 / A1 are also increasing as if the CPU is writing to 4 different places.

How can it be possible.

I have seen in the datasheet that when AXI bus and external bus is different size, it can occurs. But in that case how to perform a correct 16 bit operation ??

Other people seems to have this kind of trouble but nobody replied with a solution :

https://community.st.com/t5/stm32-mcus-products/h7-series-fmc-question/td-p/131535

https://community.st.com/t5/stm32-mcus-embedded-software/fmc-accessed-in-32-bit-but-cs-asserted-for-twice-long-64-bits/m-p/274657

Thanks in advance for any help

[Pavel A.]

I'm looking at one project for STM32H753 with FPGA, there we defined the FMC "instance" type as NOR, not as SRAM. The windows addresses are in 0x60000000 range; set in MPU as non-shared device; not remapped.

32-bit accesses to the FPGA work just fine, no unexpected behavior.

[Alex_J · Accepted solution]

Currently, I manage to make it work but it's not the way I thought.

I had to change the bank address to 0xC0000000

and deactivate MPU.

I can see one write cycle and my device is now working as expected.

But I'm not sure it's a good idea to deactivate the MPU.

I later found this related thread :

https://community.st.com/t5/stm32-mcus-touchgfx-and-gui/stm32h743ii-fmc-8080-lcd-spurious-writes/td-p/354191

By the way, it's sad that cubeide didn't warm you about the bank remapping needed in 16 bits mode needed for sram/nor/lcd..