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Display distortion problem (h300)

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S3TUP:
Time to time, at the moments the screen gets updated, i get some distortion on the screen like this: http://img54.imageshack.us/img54/2263/iriver3qs.jpg . Sometimes it affects couple of pixels, sometimes it messes whole screen.
I experience such problem with original and RockBox firmwares, so i think it must be a hardware problem. On the other hand, things gone worse by upgrading from some old build to one with increased display refresh speed by rewriting parts of sources in ASM (a month ago), so i think that something in the current firmware makes it worse than in original/old firmware.

So i opened my player and saw that DC/DC PSU big ceramic caps and Phillips UDA1380 were replaced/resoldered (i've got this player as a replacement to my bricked one from Hong Kong). Other solder spots looked ok. Nothing changed when i touched/pushed chips durning playback + i've checked their soldering, so they are ok too.

The things i see on the screen comes from display's memory (overlay?). It happens every 3-5 sec durning mp3 playback, so i looked at PCM/Codec buffers and i figured out that the codec's buffer fills up by boosting CPU frequency every 3-5 seconds, so that is a reason for artifacts on the screen. Looks like the display goes out of sync durning CPU's frequency spikes... But, one more wild thing happened - when the HD tried to spin up, the display got distorted more than at regular playback without HD, so i think the problem may be in DC/DC PSU and these big caps, because by spinning the HD/ increasing CPU speed we are loading the internal power supply, and it produces unstable voltage, that affects the display...

Anyway, i think lowering CPU speed will solve the problem.

I've got couple of questions:
 - Does anyone experience same/similar problem? On other devices?
 - Is it possible to limit CPU's clock to 90-110 MHz?
 - Where the problem comes from?
 - Any suggestions how to repair it?
 - What have been changed a month ago in display handling routine?

(This player is out of warranty for 2 weeks. Moreover, it works fine on original firmware so i can't RMA it).

LinusN:
The CPU is boosted when refilling the audio buffer from disk, so that may be why it gets distorted when the disk spins up.

We have set the LCD wait states pretty aggressively, but my logic analyzer measurements have shown that they are within the specs in the data sheets. You could try to increase the wait states in firmware/system.c as a test.

S3TUP:
Thanks! I increased wait states of LCD in 45 and 125mhz modes to 0x00000980 and 0x00002180, and it helped. Actually, i increased flash wait states to be the same as LCD's... I'll try to lower these timings to match my LCD speed.

Thanks for help! Damn, i love RockBox! :)

scretus:
hi,
i've the same problem on my h300 (or, at least, i think it's the same problem).

with new versions of rockbox (from the end of december, maybe), my display often has some distortion problems.
in fact i'm using the rockbox 2005-12-25 build, which works great with my display.
what is the cause of this problem? is there any setting i can do to solve this?

thanks!!

ps: rockbox is FANTASTIC!!!

salival:
*big bump to not have to start a new thread*

For some time now I have had altered values for the CPU wait states, since I experienced the said problems.

With the values I have set I have almost no artifacts left (only during some plugins, like doom and tetrox). My current settings are 0x00003980, ...0980 and ...0580 (max, normal, default)

Since these values are already significantly higher than default and I don't want them to be higher than needed, I have two questions regarding the values of the wait states:
1. are there any limitations or can the values be any hex number ?(i.e. they don't have to be even or the double of the previous value.)
2. Are there any known downsides on upping these values, like limited framerate or responsiveness or are those differences insignificant?

I hope someone can answer at least my first question.

thanks in advance.

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