Continuous DMA from memory to SPI

[SoCalJim]

We need to continuously DMA a single 16-bit word to the SPI transmitter. (Neither the memory address nor the peripheral address would increment.) Can this be done without intervention? I.e. do we have to use a DMA Complete interrupt to set a flag and call HAL_SPI_Transmit_DMA whenever the flag gets set, or can we configure HAL_SPI_Transmit_DMA to set and forget it?

[TDK]

Should be doable. Set up a circular transfer where neither address increments. Length of the transfer is not relevant-any nonzero value will do. Disable interrupts after it starts if you don't want to service them.

[SoCalJim]

I set up no-address-increment, Half Word (16-bit), circular DMA, from memory to SPI, transmitting 0xE002 = binary 1110000000000010 to visualize the bit spacing:

You can see there’s no space between the words.

[TDK]

That's what a continuous SPI stream looks like. Do you want something else?

[waclawek.jan]

Read out and check/post content of SPI and relevant GPIO registers.

JW