How to enable DMA transfers for UART?
|
Stefan Jaritz
Hey,
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 energy. I checked the UART stm32 api and saw that it is not utilizing things like uart DMA transfers. But there is an complete DMA API available. Yeah! Now I looked at the sample section to get a blueprint for doing so. Ups! Nothing 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? Kind regards! Stefan PS: there is an nice article on that here http://stm32f4-discovery.net/2017/07/stm32-tutorial-efficiently-receive-uart-data-using-dma/ |
|
|
|
Li, Jun R
Stefan,
I've ever implemented a DMA-enabled UART on STM32F4 boards, but based on much old version of zephyr. I can try rebasing it to the latest zephyr if you are interested. Regards, Jun On 3/19/19, 08:18, "devel@... on behalf of Stefan Jaritz" <devel@... on behalf of stefan@...> wrote: Hey, 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 energy. I checked the UART stm32 api and saw that it is not utilizing things like uart DMA transfers. But there is an complete DMA API available. Yeah! Now I looked at the sample section to get a blueprint for doing so. Ups! Nothing 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? Kind regards! Stefan PS: there is an nice article on that here http://stm32f4-discovery.net/2017/07/stm32-tutorial-efficiently-receive-uart-data-using-dma/ |
|
|
|
Paul Sokolovsky
Hello Stefan,
On Tue, 19 Mar 2019 15:18:02 +0000 "Stefan Jaritz" <stefan@...> wrote: Hey,[] So I am asking for help or some example how to do an UART & DMA.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: https://github.com/zephyrproject-rtos/zephyr/issues/13955 You're welcome to cooperate with the STM32 maintainers on implementing it. [] -- Best Regards, Paul Linaro.org | Open source software for ARM SoCs Follow Linaro: http://www.facebook.com/pages/Linaro http://twitter.com/#!/linaroorg - http://www.linaro.org/linaro-blog |
|
|
|
Stefan Jaritz
Hey
toggle quoted message
Show quoted text
I done a demo driver implementation: https://github.com/StefJar/zephyr_stm32_uart3_dma_driver 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. Stefan On 20/03/2019 15:37, Paul Sokolovsky wrote:
Hello Stefan, |
|
|
|
Erwan Gouriou
Hi Stefan, On Tue, 26 Mar 2019 at 13:01, Stefan Jaritz <stefan@...> wrote: Hey Thanks for sharing code and experience, this is useful! In my case I am interested into SPI + DMA and USB ACM + DMA. From an Indeed, we should have a proper DMA driver that could be called from other drivers. Maybe it is worth to put a thought on using DMA for peripherals by While I agree DMA has numerous benefits, I don't think this should be the only configuration, nor the default one. Main issue is initial complexity and configuration needs. People should be able to use the async API first and then enable DMA once they feel comfortable with the API. Erwan Stefan |
|
|
|
Li, Jun R
Hi Stefan and Erwan, I’m rebasing my previous implementations to the latest master branch and you can find it here: https://github.com/zephyrproject-rtos/zephyr/pull/14916 I’m still working on it since it is still lacking a couple of things and there are some bugs affecting RX. But the basic idea is to use UART IDLE to define the end of a RX DMA transaction.
If you think it is worth keeping going, let’s work together to make it happen.
Best Regards, Jun
From: Erwan Gouriou <erwan.gouriou@...>
Hi Stefan,
On Tue, 26 Mar 2019 at 13:01, Stefan Jaritz <stefan@...> wrote:
Thanks for sharing code and experience, this is useful!
Indeed, we should have a proper DMA driver that could be called from other drivers.
While I agree DMA has numerous benefits, I don't think this should be the only configuration, nor the default one. Main issue is initial complexity and configuration needs. People should be able to use the async API first and then enable DMA once they feel comfortable with the API.
Erwan
|
|
|