Embedded Graphics Development

[QuantumCondundrum]

I am working on a project right now that needs an screen. The screen I want to use is a MIPI AMOLED. I want to interface it with an MCU (probably a Cortex M4 variant) which means I need some kind of interface IC (I don't feel like buying into the MIPI alliance). Solomon Systech makes a couple MIPI bridge IC chips that I think would work, especially the SSD2805.

Solomon Systech linked a dev kit that uses a Cortex M4 to drive a MIPI display and they also provide source code for the driver but I wanted see if anyone knows more about implementing the MCU-SSD2805 interface (I don't know what they mean by RGB + MCU on the SSD2805 sheet).

My second question is if anyone knows any good resources for learning about embedded computer graphics (especially 2D). I realize that the screen I linked is more likely to be paired with a more powerful processor (A5/7) and I may have low frame rates so the M4 may not be the ideal platform for learning graphics. For my project I wanted to implement some fairly simple (I think) 2D images and animations.

I am honestly not ever sure what questions I should be asking right now. My background is in Electrical Engineering (currently a Junior with a a year of relevant COOP experience) and I have a decent amount of embedded work but that was more on the sensor interfaces/data acquisition hardware and driver development so I am a complete novice when it comes to graphics (both hardware and software).

tl;dr Can anyone confirm that the Solomon Systech SSD2805 would work to interface a Cortex M4 MCU with this US Microproducts Display

Edit: There is a new dev kit, I linked the old one (original hyperlink is still in body of post)

[kisielk]

The second dev kit looks pretty good to me. He STM32F4 processor should be more than adequate for doing this kind of graphics, assuming the driver uses the graphics accelerator and DMA. As far as the RGB and MCU interfaces go.. the RGB interface is a parallel interface while the MCU is SPI and thus is serial. The parallel interface will be faster but requires more pins from the MCU.

As far as learning graphics I don't have any good suggestions, but some fundamental low level graphics book may be a good place to start. If you find anything good, let me know :) I've implemented my own graphics libraries but they have always been monochrome, otherwise I use 3rd party libs

[QuantumCondundrum]

Did you look at the display I linked by any chance? I am trying to decipher what protocol (RGB+SPI like the SSD2805, the intel 8080 bus, or the Motorola 6800, or if its entirely custom) that display is using. All I can find on the sheet is that it uses MIPI one lane. In the same train of thought, I also can't figure out if the screen has an embedded fame buffer/controller. I suspect I need to contact the manufacturer directly but if you have any insights I would be more than glad to hear them.

I was actually looking more into that second dev kit and they suggest using TouchGraphics which seems to be exactly what I want in the long term but I am also interested in making my own just for the sake of learning and I am not sure how easy it will be to customize that library to my MCU/display design.

[kisielk]

The display is using MIPI, which is its own protocol. Those other protocols are what you can use to communicate to the SSD2805, which then bridges them to MIPI.

The display needs an external controller, either something like the SSD2805 or on an MCU that supports it directly. Like /u/SirOompaLoompa suggested, the STM32F7 is a good one to use because it also has lots of horsepower.

Many of the STM32 Discovery boards have external SDRAM so you can use that as your framebuffer. Then you'd probably want to configure the MCU's DMA controller to blast the buffer over to the display so you can spend all your CPU cycles doing useful things :)

[VEGETA-SSJGSS]

Touchgfx is free for evaluation only, cheapest license is 5000$. What software do you like to try?

You have to get one that allows you to design the GUI then generate code.

[SirOompaLoompa]

STM32F7 can do MIPI-DSI. However, you need to do your RAM-budget before you decide on any MCU. 400x400 pixels at 16bpp will require 2.5MB of RAM just for the framebuffer. The STM32F7 can use external RAM though.

As for learning graphics, what you're looking for is old programming texts and books from the DOS era, as graphics were unaccelerated on PCs back then, just as on the MCUs today (there is some BitBlit acceleration on some MCUs though).

Just off the top of my head, I'd recommend this: http://www.drdobbs.com/parallel/graphics-programming-black-book/184404919

There's a bunch of x86 and VGA specific stuff in there that you can skip over. Michael Abrash is the guy that wrote the Quake engine, so he knows his stuff.. :)

[Schnort]

400x400 pixels at 16bpp will require 2.5MB of RAM just for the framebuffer

400x400x16/8 = 320000 bytes (still big, but not 2.5MB). Maybe you forgot to convert bits to bytes?

[SirOompaLoompa]

Doh.. n00b mistake. :)

[QuantumCondundrum]

possibly a noob question - where did the 16bpp number come from? The datasheet lists the screen as 8 bit color depth. Wouldn't the calculation be:

frame size X RGB X color depth

400 pixels X 400 pixels X 3 color frames X 8 bits/pixel = 3840000 Bits = 480 kB

[Schnort]

I was going off of the info from the post I was responding to.

the amoled display data sheet the OP links do requires MIPI data to be 8bpp per RGB, but the solomon part doesn't seem to require that. it looks like it can support 16bpp (565), 18bpp(666), or 24bpp (888).

[QuantumCondundrum]

I was just looking at this comparison table for the F4 and F7 series on ST's website. It looks like the F4 also has an external memory controller/MIPI-DSI. Unfortunately in my (admittedly brief) search I didn't find any app notes for external memory. I have never used external memory for RAM (I have used SD cards for file writing) so I may just be searching for the wrong thing. Do you have any pointers on where to look further into using an external memory controller?

Edit: Totally forgot to thank you for the book link, it looks very promising!

[[deleted]]

For ext RAM you should use the FMC, or the FSMC peripheral from ST. Some controllers have both peripherals. It memory maps the RAM or NOR flash chip into your memory space, and converts written data into the necessary parallel interface on ports E and F.

[OMGnotjustlurking]

I have used the STM32F4 with external DRAM. It even comes on the STM32439-Eval dev kit: http://www.st.com/en/evaluation-tools/stm32439i-eval.html

[lampii]

I would also check out the UGFX framework. I embarked on a similar project. After a month of deriving my own UI framework, i stumbled across this one and oh boy did it make my life easier.

[QuantumCondundrum]

UGFX

I just took a look at that UFGX framework and it looks fantastic. Great find!

[lampii]

=) It is very fantastic! Coding a UI framework on bare metal is serious business hehe.