ESP32 Forum

Hello! I bought ESP32-wroom-32 board a week ago, and I instantly started learning its capabilities. I learned how to use DPORD, GPIO, SPI peripherals using registers, but DMA stopped me.

The idea is to send 2kiB of data through SPI in one transaction. I have a buffer prepared, data in it is valid (when send through FIFO the connected device works properly). During the process, I connect clock signal to the SPI and DMA peripherals, then connected SPI2 with DMA ch1. I set SPI CLOCK_REG, in USER_REG MOSI (27) bit and full duplex (1) bits. Connected the signal to the GPIO pin.
To send data I set SPI_DMA_OUT_LINK_REG to the descriptor address, and the START bit. Then, I set the SPI_MOSI_DLEN_REG for the amount of BITS transfered -1, and I enable SPI by setting bit 18 in SPI_CMD_REG.

My descriptor looks like this:
The data is flowing, but it is incorrect, and when a transaction is repeated the data is taken from another address (cyclical change)
The DMA always loads new descriptor after the transaction, EOF deesn't seem to be issued. I am checking the registers during tests, the next descriptor address is set (despite 0 in given descriptor in nextDSCADDR position) and oscilloscope shows that data is pretty random.
What is the proper way of initialising DMA and DMA single transaction in ESP32? When I tried resetting DMA by using lower bits of SPI_DMA_CONF_REG it didn't work at all.

Thank You for Your time and help!


Ps. is there something like CMSIS for ESP32?
Pss. I am using https://www.espressif.com/sites/default ... ual_en.pdf as the ref manual.

Could it be that you're allocating the descriptor on the stack and then exiting the stack frame?

Hi! Thanks for the answer!
The Descriptor is allocated at the stack, in function "app_main", yet the the transaction start is also called from this function, from an infinity loop (delayed by vTaskDelay() ). To check I madea global variable from the descriptor, however the program behaviour is unfortunately the same.

I can also add that the register SPI_OUTLINK_DSCR_REG (current descriptor pointer) shows the correct memory address.

Code: Select all

DMA_FIRST_AND_ONLY_DSC.bufAddrPtr = (uint32_t)data; //data is the buffer name

Does (uint32_t)data yield the correct address? Data buffer pointed to is valid throughout the transaction?

is there something like CMSIS for ESP32?

Use the drivers from the ESP-IDF, e.g. for SPI.

Yes, the addresses are correct. Here is my memory dump: (sent through UART) As shown data buffer is constant through the program. It was also moved to global variables section, no change occured.

I managed to successfully apply the DMA to the UART peripheral (using registers), as well as run the required transfer using the idf framework, but still, I wish I know what I do wrong when configuring DMA registers. Also, I checked the data array using STM32 and it was 100% correct.

One more thought: Check the configuration of the inbound path, SPI_DMA_IN_.... Since every transfer via SPI is bidirectional, the incoming data may unintentionally overwrite some data in RAM if inbound DMA is not disabled.