drivers: video: Add support for STM32 DCMI

[CharlesDias]

Dear,

The goal is to provide the STM32 DCMI driver. I'm creating the sample to capture a frame image and sent it to LCD ( PR #71463). That sample has been tested on the mini_stm32h743 target with the OV2640 camera model.

Note: This current version was implemented only for STM32H7 family and doesn't support the JPEG pix format.

Related PR:

• drivers: video: ov2640: add clock rate control property #71962
• samples: subsys: video: add capture to lcd sample #71463

document_4958923842157282345.mp4

[CharlesDias]

Dear, @erwango, @ABOSTM, and @FRASTM.

In the sample on the PR #71463 I declare the DCMI and MCO1 pins inside the overlay file because those pin's configuration don't exist on the ST pinctrl dtsi files.

[CharlesDias]

Fix code style and remove the code to generate mock images.

[CharlesDias]

Fix compliance errors.

[loicpoulain]

Any plan to support continuous capture?

[CharlesDias]

I don't have intention for this version. Maybe in a future as an improvement.

Both sample codes for video capture are based on performing an enqueue command before dequeue. In this way, I believe that a snapshot strategy is enough.

[loicpoulain]

what If i we enqueue two buffers? should'nt we start DMA transfer only for the first one? and restart internally on frame done?

[CharlesDias]

The function HAL_DCMI_Start_DMA can be called only on time. If this function is called again, the HAL_ERROR is returned.

In the ST sample code, only one video buffer is used. Below is described the workflow in those samples:

1. Start the DCMI via HAL_DCMI_Start_DMA in DCMI_MODE_CONTINUOUS.
2. When the HAL_DCMI_FrameEventCallback is trigger, call the HAL_DCMI_Suspend.
3. Retrieve the video buffer.
4. Resume the DCMI via HAL_DCMI_Resume.
5. Repeat item 2.

I can try to reproduce that workflow, but I believe that the result will be the same. Please, let me know if I missed something.

[CharlesDias]

Think better, I believe it's more sensible to retain the existing workflow, since the video buffer is passed through the enqueue function. I mean, call the HAL_DCMI_Start_DMA inside the enqueue.

[loicpoulain]

Does it work with the simple generic video capture sample in samples/subsys/video/capture/ ?

(If we enqueue several buffers, I would expect that seconds one is used once the first one as been completed, and so on.)

[CharlesDias]

I created this sample version. It'll work if you enqueue just one buffer. Link to the sample code #71463.

Next week I'll try to look more into DCMI ST API to check if I can do better.

[CharlesDias]

Hi, @loicpoulain.

I changed the driver to work as continuous capture and with more than one video framebuffer.

[CharlesDias]

Since HAL_DCMI_Start_DMA can only work with one buffer, I created a dedicated buffer to store the frame data. This is the current workflow:

1. application enqueue one or more buffers.
2. call start capture function.
3. The DCMI driver creates a buffer with CONFIG_VIDEO_BUFFER_POOL_SZ_MAX size to store the frame data and starts the capture in continuous mode.
4. when the interrupt occurs, call DCMI suspend function
5. If a video buffer is available, copy the frame data from the DCMI buffer to the video buffer.
6. resume the DCMI capture.
7. go to item 4.

This driver was tested with this sample code #71463

[CharlesDias]

Rebase the branch and small changes to the YAML to became similar to Linux YAML.

[CharlesDias]

Add DCMI node to other DTSI files: stm32h723.dtsi; stm32h745.dtsi; stm32h750.dtsi; stm32h7a3.dtsi.

[CharlesDias]

Update the driver to work in DCMI_MODE_CONTINUOUS and with more than one video framebuffer in the application.

[CharlesDias]

Add the capture-rate property. This allows us to set up the frame capture rate.

[erwango]

A great thanks for this contribution.

[CharlesDias]

Implement the previous suggestions, except the one about changing the check for the config->sensor_dev value (I am waiting for feedback about my comments). Thanks @erwango

[erwango]

Last round of comments and this'll be fine to me. Thanks again @CharlesDias !

[CharlesDias]

Implement @fabiobaltieri's suggestions.

[ajarmouni-st]

Thanks !

[josuah]

This got changed in #72623
Will need some new PR to update depending on the outcome.