[U-Boot-Users] AT91 with framebuffer in SDRAM

[Ulf Samuelsson <ulf@atmel.com>]

> On 10/23/07, Ulf Samuelsson <ulf@atmel.com> wrote:
>> > On 10/22/07, Ulf Samuelsson <ulf@atmel.com> wrote:
>> >>
>> >> The environment variables should be stored in flash, not in SDRAM.
>> >> - Even if you execute from SDRAM.
>> >>
>> >> What type of flash are you using.
>> >> My stuff is there to support dataflash, and anything else
>> >> get little or no testing.
>> >
>> > I am using dataflash for everything. Everything is pretty equivalent
>> > to your code base, just the LCD timing values and the fb_base have
>> > changed.
>> >
>>
>> > Maybe I should rephrase. Everything seems fine once it is in
>> > dataflash. But if I `setenv bootcmd something' and then `saveenv`, it
>> > says "saving to dataflash...". `printenv` prints back the correct
>> > value (bootcmd=something), which I understand it isn't actually
>> > reloading from dataflash. If I then reset the board that
>> > bootcmd=something is gone. The environment variables are not in
>> > protected dataflash.
>> >
>> > In board/at91sam9261ek/at91sam9261ek.c
>> > If I change
>> > gd->fb_base = (unsigned long) PHYS_SDRAM  + 0x10000;
>> > back to
>> > gd->fb_base = (unsigned long) AT91C_IRAM;
>> > the LCD goes wonky but saving to dataflash works again.
>>
>> Don't know if this is the problem, but you can at least try it:
>>
>> The main difference I can see is that when you put the framebuffer in
>> external SDRAM, you are affecting the bus bandwidth.
>> When doing the LCD from internal SRAM, you have zero access.
>>
>> Consider changing the speed of the SPI to much lower speed (1 Mbps).
>> If this works, then increase the speed, until you see the problem.
>> Reduce to something lower.
> 
> This did the trick, thanks Ulf. I'm using 8 MHz as it seems stable.
> 
>>
>> An alternative is to link the environment into the internal SRAM.
>> Then the SPI transfer will not be affected by the LCD refresh.
> 
> I couldn't take this approach because this only sort of skirts the
> problem. If I did something else (e.g. used u-boot to upgrade itself)
> it would corrupt the write and then I'm back to JTAG to reload it.
> 

I think that you should still do this.
You may need to do a slight modification to U-Boot
so that the dataflash write driver copies a chunk of data to
the internal SRAM before it writes it to the dataflash.

The CPU is sitting idling while waiting for the PDC to complete the SPI transfer anyway.

Best Regards
Ulf Samuelsson                ulf at atmel.com
Atmel Nordic AB
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