STM32H745 FMC PSRAM 16-bit always sends 64-bit

[Kurngop32]

Hello,

I am trying to get the FMC to work in 16-bit synchronous mode but I only get an output with 4 clocks (64-bit) instead.

In other threads [1], [2] I found that I should either switch the address from 0x60000000 to 0xC0000000 or enable the MPU, but neither approach works for me.

This is my config:

FMC:

MPU:

Usage:

uint16_t * psram16 = (uint16_t *)0x60000000;
psram16[0] = 0x00AA;

Output:

What am I missing?

[1] https://community.st.com/t5/stm32-mcus-touch-gfx-and-gui/stm32h743ii-fmc-8080-lcd-spurious-writes/td-p/354191/page/2

[2] https://community.st.com/t5/stm32cubemx-mcus/stm32h743iit6-fmc-ne-producing-multiple-clocks/m-p/312170

[KDJEM.1]

Hello @Kurngop32 and welcome to the Community 🙂,

According to RM0399, for some PSRAM memories which must be configured to Synchronous mode, during the
BCR register writing, the memory attribute space must be configured to device or strongly-ordered. Once PSRAM BCR register is configured, the memory attribute of PSRAM address space can be programmed to cacheable.

Could you please check these settings?

Thank you.

Kaouthar

[Kurngop32]

Not sure what this means. Isn't that the MPU setting?

I also tried it without CubeMX:

MPU->CTRL = 0;
MPU->RBAR = (0x60000000 & MPU_RBAR_ADDR_Msk)
	| (1 << MPU_RBAR_VALID_Pos)
	| (0 << MPU_RBAR_REGION_Pos);
MPU->RASR = (1 << MPU_RASR_XN_Pos)		// execute never
	| (0b011 << MPU_RASR_AP_Pos)  		// access: full
	| (0b000 << MPU_RASR_TEX_Pos)		// type extension
	| (1 << MPU_RASR_S_Pos)			// sharable
	| (0 << MPU_RASR_C_Pos)			// cacheable
	| (0 << MPU_RASR_B_Pos)			// bufferable
	| (0 << MPU_RASR_SRD_Pos) 		// subregion
	| (MPU_REGION_SIZE_128KB << MPU_RASR_SIZE_Pos) 	// size: 2^(val+1)
	| (1 << MPU_RASR_ENABLE_Pos);
MPU->CTRL = MPU_CTRL_PRIVDEFENA_Msk | MPU_CTRL_ENABLE_Msk;

[KDJEM.1]

Hi @Kurngop32 ,

Yes, I mean that the memory region MPU attribute must be configured as “Device" or “strongly-ordered".

I think that  FMC_PSRAM example can help you. This example describes how to configure the FMC controller to access the PSRAM memory. The PSRAM is IS66WV51216EBLL-55BLI. This example has been tested with STM32F723E-Discovery board and can be easily tailored to any other device and development board.

I hope this help you!

Kaouthar

[Kurngop32]

This leaves more questions than it answers. In the example, additionally to what I already did, another memory region at 0xA0000000 is created, no idea why since this is reserved space, but it does not help anyway. To be sure I set the whole memory to strongly-ordered, but that does not change anything. The output looks still the same, i.e. 4 clocks instead of 1.

[Kurngop32]

btw this is how a 32 bit access looks:

uint32_t * psram32 = (uint32_t *)0x60000000;
psram32[0] = 0x00A000A1;

5 clocks, so also 3 unnecessary clocks (or my expectation is wrong, I don’t have much experience with external memories)

[KDJEM.1]

Hello @Kurngop32 ,

Do you see the same behavior when using DMA?

To check this issue, could you please share your project?

Thanks and best regards,

Kaouthar

[Kurngop32]

No difference with MDMA.

uint16_t src=0x1234;
HAL_MDMA_Start(&hmdma_mdma_channel0_sw_0, (uint32_t)&src, 0x60000000, 2, 1);

You can make a new project (STM32H745XIH6, FW H7 1.11.1), with the settings from the first post. I didn't change or configure anything else.

FMC is accessed right before the main while loop.