DSP board mods?

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mrbombermillzy
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DSP board mods?

Postby mrbombermillzy » Sat Jul 01, 2017 2:03 pm

Hi Guys,

Im just wondering if anyone knows of any modifications which would have required the cutting of pin 46 and 76 of the DSP (thats the BR and MODA/IRQA lines) which are connected to Vcc? (via R177)

I have a machine that runs fine for non DSP apps (ST games, Exxos' GemBench, HDD drivers and even plays some Falcon games) but when I try something that uses the DSP, it either hangs or runs seemingly ok, but with no audio input/output. Even Audio Fun Machine just has green bars which dont move and no sound i/o.

Connecting these pins causes worse results; the DSP specific apps wont even start.

(Ive tried DSP bench and SDMA test programs; DSP bench 'completes' immediately with no result info and sdma test runs but doesnt output any sound. Centest strangely rates the DSP as running at 293MHz! AFM just gets to the gem app box and doesnt display anything in the box whereas with the lines disconnected it did)

The board has had some mods applied. Theres a 3in1 blowupFX board in the expansion slot, with the little mods required to work that, and some of the 'official' board revisions have been done, including the L35 and L36 bass boost removal mod.

Im just trying to figure out how removing of the bus read and interrupt request lines could possibly be something to improve matters?!?

Was some sort of line redirection required for the CT boards, as I notice on Rudolphes site, in the software archive there was a 'DSP irq.prg'?

Many thanks for any pointers folks! :)

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Re: DSP board mods?

Postby mikro » Sun Jul 02, 2017 9:58 pm

Man, you should post hires photos when asking stuff like this.

It's true the CT2 required to wire the DSP IRQ line to make it 100% compatible (http://didierm.pagesperso-orange.fr/files/interdsp.zip) but this doesn't seem to be the case here.

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Re: DSP board mods?

Postby mrbombermillzy » Mon Jul 03, 2017 6:03 am

Ok, as requested, heres a some pictures of the board, including the DSP before I joined pins 46+76:
P1030094.jpg


P1030095.jpg


P1030096.jpg


P1030097.jpg


Im guessing my non working programs may actually be the SDMA system which I will have to investigate at the weekend. However, I wonder why pin 76 has been lifted from the board. I cant see it as being good, and not anything to do with the 3in1 board either. The wire by the DSP is actually going to the xtal circuit on the blowup board.

Im sure someone else had this on their board, and actually asked why, but it was never answered. Heres hoping someone can shed some light. If it is, as you say Mikro, for an external accellerator, then I really need it returned to normal... and to figure out the crashing really. :|
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Re: DSP board mods?

Postby mikro » Mon Jul 03, 2017 8:03 am

What a mess. The aforementioned DSP pins are used for DMA mastering, I'm actually quite surprised they are needed for DSP overlocking by this card. Maybe they do some other wizardry.

I'd contact (or lure here ;)) joska, according to this thread: viewtopic.php?t=22959 he used to own one and he's pretty knowledgable so perhaps he could give you some hints (at least point you to the user who owns it now with the manual).

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Re: DSP board mods?

Postby joska » Mon Jul 03, 2017 8:41 am

mikro wrote:(at least point you to the user who owns it now with the manual).


Right... I sold it to a guy here who "needed" it for a project. He instantly put it up on AmiBay for twice the price. So I have no idea who ended up with the card, but atleast I know who ended up with the profit ;)

Anyway, I would suggest to completely remove the FX and restore the Falcon to stock conditition. Then trouble-shoot from there if the DSP problems are still present.

Edit: No, this DSP massacre has nothing to do with the FX. The FX could optionally clock the DSP at 50MHz, but that only involved replacing the DSP clock signal.
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Re: DSP board mods?

Postby mrbombermillzy » Mon Jul 03, 2017 9:06 pm

Thanks Mikro for 'luring' Jo here! :) And thanks to both of you for the infos;

So basically the DSP interrupt was used to service the CT2 board? (Obviously it was taken out and the line wasnt restored).

I must admit I dont care for anything 'boosted' or overclocked on the Falcon...as far as Ive seen its frail enough already! So when I first opened this machine, I took a big gulp when I saw the mess inside!

However, I did consider leaving the abomination in there if I could get some extra Fast ram ontop of the internal 14mb ram board (14mb + 16mb on the blowup= 30mb?! Is this possible with some malloc() patching?), but as its probably causing the DSP(/SDMA?) problems I will agree with you that it has to go.

I did manage to pick up what looks like most of the manual for the 3in1 blowup board. It looks like I have the board mods in there, so I should be able to reverse those. (I also have a MUCH better Falcon service manual schematic than before, which helps tremendously!)

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Re: DSP board mods?

Postby joska » Tue Jul 04, 2017 6:47 am

mrbombermillzy wrote:However, I did consider leaving the abomination in there if I could get some extra Fast ram ontop of the internal 14mb ram board (14mb + 16mb on the blowup= 30mb?! Is this possible with some malloc() patching?), but as its probably causing the DSP(/SDMA?) problems I will agree with you that it has to go.


The addressbus of the CPU in the Falcon is 32 bits wide, so the CPU itself can access 4Gb. However, in the Falcon only the lowest 24 bits are connected, limiting the address range to 16Mb. So if you have 14Mb ordinary Falcon-RAM the FX RAM is useless. Yes, it's possible to add more than 14Mb RAM to a Falcon. However, this would require some bankswitching trickery and the use of the MMU and CPU, which means slower speed. The FX was supposed to do this, but atleast the FX I had did not.

My suggestion is to restore the Falcon to stock and get the DSP working. Then you can consider adding the FX again, but to be honest I don't think it's worth it as you already have 14Mb RAM. There are better speeders.
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Re: DSP board mods?

Postby mikro » Tue Jul 04, 2017 11:01 am

I only emphasise that:

mikro wrote:It's true the CT2 required to wire the DSP IRQ line to make it 100% compatible (http://didierm.pagesperso-orange.fr/files/interdsp.zip) but this doesn't seem to be the case here.


I don't think the DSP butchery comes from a CT2 installation. This looks like something totally different, like adding a different DMA device or so. Hard to say.

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Re: DSP board mods?

Postby mrbombermillzy » Tue Jul 04, 2017 7:51 pm

@joska: I hear you loud and clear. The only single regret I would have had in ripping the board out was the prospect of the extra RAM. Thanks for clearing that up then. I will remove the board this weekend and hopefully restore the board, if I can figure out how many ECO changes were made to this rev. c/d board.

@Mikro: Yeah, it looks like SOMETHING needed to steal the DSPs interrupt line, but what? I see that paul92706 also has (had?) a falcon with the same pins (46+76) being the target of a similar mod, but his one appeared to have the trace broken before reaching the resistor (R177) from the Vcc rail:

http://www.atari-forum.com/viewtopic.php?f=97&t=24211&start=25

Im curious now as to what used this interupt! :D

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Re: DSP board mods?

Postby Rustynutt » Tue Jul 04, 2017 9:47 pm

Rodolphe "with solders" :)


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