Zephyr: Add STM32 LCD-TFT Display Controller (LTDC) Driver

Created on 22 Apr 2019 · 7Comments · Source: zephyrproject-rtos/zephyr

Is your feature request related to a problem? Please describe.
Add support for STM32's LTDC on STM32F4, F7, H7, etc.

Describe the solution you'd like
Initially, an API specific to the LTDC implemented with a long-term objective of enhancing the generic display API to support more advanced LCD drivers either on-board or in-MCU while supporting smaller displays with little overhead. This driver should be modular; able to be built such that unused feature sets can be removed. The STM32 HAL will not be used (greenfield implementation). Existing generic display API will have shortcomings (e.g., pixel format support). Use shim to provide API implementation; native and generic APIs will be exclusive from each other.

Would like to support:

Compositing layers with transparency (LTDC supports 2 layers).
Multiple color models (Monochrome, CLUT/indexed, RGB), color spaces and pixel formats.
Specialized DMA (DMA2D) for fill/blit/blend operations, including pixel format conversion and alpha blending.
Double buffering, able to utilize separate SRAM/SDRAM banks - configurable at buildtime or runtime. VSYNC timing/notification.
MPU/D-Cache management for DMA operations
Buildtime/runtime LCD configuration (buildtime at board config)
Blanking/contrast/backlight control (need separate callbacks/drivers for this - power and backlight controls are on the board)

Other considerations for features not supported by LTDC, but are common (to support in generic API enhancements):

Extensible color model/space/pixel format for packed (and planar?) YUV.
Hardware accelerated stretch/scale.
OS/API-enforced constraints, e.g. Layer zero dimensions same as display, layer reordering limitations, maximum supported display size, limited number of display driver instances,

Describe alternatives you've considered
Crayons attached to steppers.

Additional context

Feature Request Display

Source

matthew-koch

👍5

Most helpful comment

Quick update.

Made progress on the driver, but have gotten stuck by not having a working memory controller for external SDRAM. Didn't quite realize how sparse support for STM32 was before diving into this, so I'm having to switch gears and work on getting enough memory to handle the framebuffer and sort out the current memory mapping (DTCM vs. SRAM).

matthew-koch on 4 May 2019

👍3

All 7 comments

Describe alternatives you've considered
Crayons attached to steppers.

🥇

carlescufi on 22 Apr 2019

FYI (no response required)

If it wasn't implied in the issue writeup, I intend to take a stab at this. I'm doing development on an stm32f746g_disco board.

Will be slow going to start - Zephyr's build system has a bit of a learning curve with some tools I'm not familiar with. However, nobody seems to be pounding the table for this driver. I will try to get a PR on a couple of things that might cause ugly merges later (pinmux, device tree) done first.

matthew-koch on 23 Apr 2019

👍1

Quick update.

matthew-koch on 4 May 2019

👍3

@matthew-koch I'm working on this issue, are you still interested in having this working? I've got the memory side of things working, and have some code working for the LTDC which I'll commit in a day or 2 after cleaning it up.

Checkout the pull request #23453

k0d on 13 Mar 2020

👍2

By all means! I ran into a big project at work and haven't had a lot of
time for this. I kept chasing things that weren't implemented in Zephyr
(clocks, SDRAM, etc.) and this ballooned beyond what time I had. I won't be
able to pick this up again until late spring or early summer, so I'd
appreciate having this working.

On Fri, Mar 13, 2020 at 2:19 PM Mark Olsson notifications@github.com
wrote:

@matthew-koch https://github.com/matthew-koch I'm working on this
issue, are you still interested in having this working? I've got the memory
side of things working, and have some code working for the LTDC which I'll
commit in a day or 2 after cleaning it up.

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