STM32N6 JPEG DMA corruption when using PSRAM for frame buffer

[pikud]

Hi ST Community,

I’m working on a JPEG encoding pipeline using the STM32N6570 Discovery Kit, and I’m running into an issue when storing both my input and output buffers in PSRAM.

Setup:

• Both JPEG Encoder input (RGB_ImageAddress) and output (jpgBuffer) buffers are placed in PSRAM.
• I’m using RGB888 input format, the same as in the official JPEG example here: JPEG_EncodingFromOSPI_DMA 

Linker script (.ld) snippet:

MEMORY

{

  AXISRAM1_S (xrw)      : ORIGIN = 0x34000400, LENGTH = 1023K

  PSRAM (xrw)           : ORIGIN = 0x91000000, LENGTH = 16M

}

.psram_section (NOLOAD):

{

   . = ALIGN(32);

   *(.psram_bss)

   . = ALIGN(32);

} >PSRAM

Buffer declarations:

__attribute__((section(".psram_bss")))

__attribute__((aligned(32)))

uint32_t jpgBuffer[160 * 160];

__attribute__((section(".psram_bss")))

__attribute__((aligned(32)))

uint32_t RGB_ImageAddress = {0}; // RGB888 image

Problem:

After running HAL_JPEG_Encode_DMA(...) and reading from jpgBuffer, I get corrupted or incomplete JPEG data:

• The end marker (0xFFD9) is present.
• But the initial bytes (like the JFIF header) are missing or garbage.
• The total JPEG size detected is inconsistent.

What I’ve tried:

• Encoding works perfectly when buffers are in internal SRAM (AXISRAM1_S).
• PSRAM is memory-mapped and accessible (I verified reads/writes).
• D-Cache is enabled using SCB_EnableDCache() in main.c.
• JPEG output buffer is in PSRAM — this seems to be the breaking point.

Questions:

1. Does JPEG DMA support output to PSRAM (0x91000000)?
2. Do I need to explicitly clean/invalidate D-Cache or configure MPU for this memory region?
3. Should JPEG output always be kept in internal SRAM, even if input is in PSRAM?

Main.c is attached below for reference. Any help or insights would be greatly appreciated!

Thanks

[Khaled_DHIF]

Hello @pikud,

Since PSRAM is correctly accessible and you are using DMA with a cacheable memory region, ensure proper cache maintenance to avoid data corruption:

1. Before DMA Transfer: Clean the cache for the input buffer ('RGB_ImageAddress') using 'SCB_CleanDCache_by_Addr()'.
2. After DMA Transfer: Invalidate the cache for the output buffer (`jpgBuffer`) using 'SCB_InvalidateDCache_by_Addr()'.

Best regards