Re: How to enable DMA transfers for UART?

Stefan Jaritz


I done a demo driver implementation:

Some problems I was facing:

- DMA API: the current one doesn't support ring buffer setups

- UART API: the current API is not mapping the IDLE event.

- UART API: no callbacks possible for event driven rx

With the current design of the UART and DMA API it seems to be challenging to get a nice fusion.

So I was implementing a simple API for the demo, making block writes possible and calling a callback when data is received. I didn't used the UART and DMA API because it would became a dirty hack, while calling functions form that API & overwriting/patching the ISRs. So I decided for a lean straight forward implementation.

In my case I am interested into SPI + DMA and USB ACM + DMA. From an energy perspective it is much better to use DMA transfers for the peripheral IOs (We can put the MCU to sleep).

Maybe it is worth to put a thought on using DMA for peripherals by default and only the special case is doing polling or RX/TX handling via uart etc. ISRs.


On 20/03/2019 15:37, Paul Sokolovsky wrote:
Hello Stefan,

On Tue, 19 Mar 2019 15:18:02 +0000
"Stefan Jaritz" <stefan@...> wrote:


I am currently experimenting with ZephyrOS on different tasks. My
base is an own dev board which has a stm32f4xx MCU that connects
different ICs etc. via UART, I2C, SPI & GPIOs.

Currently the UART ISR is too slow to catch all chars at a rx burst.
Usually I am using UART + DMA transfers to relieve the MCU and save

So I am asking for help or some example how to do an UART & DMA.

Think having an ringbuffer for rx and an intr firing after n Bytes
received via DMA. Also doing the tx via DMA would be perfect. Any
ideas to setup the Zephyr drivers to do so?
Recently, a new "async" UART API was added to Zephyr, whose
implementation could leverage DMA support (that was one of usecases for
this API). There's an open ticket to implement it for STM32:

You're welcome to cooperate with the STM32 maintainers on implementing


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