ESP32 Forum

Hi

Is there any limitation (chip side) that the SPI Driver using DMA cannot use TX buffers in SPIRAM memory?

From what I understand in the datasheet/reference manual, the GDMA module should be able to access internal RAM and external RAM, the SPI section doesn't seem to mention any limitation on this regard, but the ESP-IDF (v5.4.1) SPI driver implementation limits that the Buffer in case of DMA must be in internal RAM (inside SPI Driver)
And the function "esp_ptr_dma_capable" is only checking that the buffer must be in internal RAM, and if the buffer is in external RAM will attempt to allocate a buffer from internal memory.

Is this limitation from the chip itself, or is it a limitation of ESP-IDF on not supporting this correctly?


Thank You

Good point. Might be something we overlooked because it looked like it did the right job to begin with or maybe it's a conscious choice because PSRAM might 'go away' when flash writes are done. I'll make an internal issue about this.

Thanks for the feedback.

If possible after the internal discussion, post some follow-up, or maybe put a note in the SPI driver documentation regarding this.

Thank You

Although he hardware can do PSRAM<->peripheral DMA, I think I saw stated somewhere that the IDF explicitly does not support this. (Might have been in some comment in IDF code.)

I modify the code to add esp_ptr_dma_ext_capable in the condition so memcpy is skipped with psram tx_buffer. As long as the buffer is uint32_t aligned, i can see image pushed to the screen, but it seems that spi_device_get_trans_result is not properly working and there are glitches on the screen.

Any news here?