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STM32F439XX with video and external framebuffer

cleanser23
Associate II
Posted on January 13, 2015 at 20:32

I can't seem to find more information on this, even looking through the EVAL code...

here it goes:  

I am designing a simple system to learn how to use the STM32F439XX and perhaps use it in future projects, but I am not sure if it is fast enough since the AHB can only support concurrent accesses to 1 external memory.

I am hoping to attach 128k of memory as a frame buffer at the beginning of this section of memory.  I already know there isn't enough time to render and fill (think a simple game like super mario world or something along those lines) the frame.

That said, I can attach 256k and double buffer by swapping the location of the buffer between frames, that gives me more than enough time to render each frame.

The problem occurs when I realized that I can't concurrently read from external memory for the frame buffer on FMC mapped SRAM/DRAM at the same time as writing to it.  Does anyone know if the contention will be a big problem?  I have never done something quite like this before, so I'm not sure on the details of sharing a bus (I know it's a round robin algorithm).

The pixel clock is 9 Mhz and system clock is whatever the minimum it needs to be to achieve ~60 fps (for debugging puruposes at the moment let's just say the maximum 180 Mhz).  I think the external memory will run at ~50 Mhz depending on which I buy.

Any suggestions are greatly appreciated.

Brandon

#lcd #tft #discovery #stm32f4 #stm32
5 REPLIES 5
Posted on January 14, 2015 at 08:12

These are still microcontrollers and the video is not a key element here. To avoid disappointment, you should perhaps resort to ''adult'' processors and graphics subsystems, such as those found on Raspberry Pi and similar.

Otherwise, if you stick to the 'F43x, calculating/estimating/benchmarking bandwidth and performance is your basic homework. The cheap Discovery boards are aimed at assisting you in this.

JW

cleanser23
Associate II
Posted on January 14, 2015 at 23:35

Thanks for the reply!

You're right, an ''adult'' microprocessor (ARM7/8/9/11 or Cortex A) WOULD be much better suited to this task, unfortunately, there are a number of limitations that prohibit that.

We are a team of only 2 engineers, only one of which is specialized in computers and processors (the other much more analog focused) and our deployment time is ~1.5-2 months.

The learning curve on those larger processors is quite large, and the jump in performance is also quite large, there doesn't seem to be a nice middle ground.  We are also limited because, since we are hand assembling this, only QFP chips are allowed (no BGA).  If you have a suggestion that would render me wrong on all this (I am not exactly an expert on all things available), I'd love to hear from you!!!

That said, we are ordering and EVAL (a little more suited to our needs), and have done a lot of reading on the processor and its AHB bus system etc.  After lots of deliberation and math, we've decided that this processors should be more than enough, actually.  Here is an example: 

https://www.youtube.com/watch?v=vMI9GdDQVHU

again, thanks so much for the reply

Posted on January 15, 2015 at 01:17

I'd watch for parts with 12-26 week lead times...

ST's rolling out their STM32F7 Cortex-M7 parts, figure perhaps 2x the F4 speed.
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AvaTar
Lead
Posted on January 15, 2015 at 13:20

We are a team of only 2 engineers, ... and our deployment time is ~1.5-2 months.

 

Doesn't that sound a little bit too optimistic ?

Of course that depends on the quality you are assumed to deliver after that period.

cleanser23
Associate II
Posted on January 15, 2015 at 18:42

You're right, it is optimistic!!! The actual time-frame is about 3.5 months, but we need time to solve problems.

As you may have guessed, this is a school final design project