STM32MP157 Display Interfacing and OS Organization

[Alex Münnich]

Hi,

we're thinking about using the STM32MP157 in a product. However, there's still something unclear to us.

We need to connect it to a display which only supports the 16-bit Intel 8080 bus (so LTDC cannot be used). I read that it's possible to emulate its graphics memory via FMC. Our plan was to let the GPU write directly to FMC so that no DMA intervention will be neccessary and no extra frame buffer needs to be allocated. Unfortunately, there's not much documentation on the 3D GPU.

So our questions are: Can the GPU output pixel data directly to FMC? How does the pixel data format look like?

Also important to us: Can Android run on both CA7's or is it only possible to run a TEE OS on the secure core? And would it be possible to run CM4 either completely independent or split (custom code + Android communication)?

Thanks in advance,

Alex

[Olivier GALLIEN · Accepted solution]

​Hi @Alex M.ünnich​ 

Sorry for the delay to answer.

This is what we can answer so far.

1 - Can the GPU output pixel data directly to FMC? How does the pixel data format look like?

Yes this is possible but will require development of an FMC LCD display driver which is not in ST roadmap.

2 - Can Android run on both CA7's or is it only possible to run a TEE OS on the secure core?

There is no “secure core�? but a dual Cortex-A7 with a secure context and a non-secure context for each core, running in SMP mode (symmetric multiprocessing).

So Android can run on both cores and, when it is invoked, the secure monitor will become active on one of them (typically the first one if the GIC distributor is configured to always target it with the secure interrupts).

3- And would it be possible to run CM4 either completely independent or split (custom code + Android communication)?

Both modes are possible, keeping in mind that the CM4 will remain under the CA7 control (for stop and start).

Hope it help,

Olivier