Flegmatix DFB1 adventure

[flegmatik]

I started building a Dave's Falcon Booster (DFB1) from scratch. My goal is Falcon at 40MHz, since 68882FN40A FPU and 40MHz capable plastic 68030 are quite cheap (compared to 50MHz capable ones).

I would really like to say thanks to @Badwolf for creating this awesome piece of hardware.

I finished 1st and 2nd stage of the build, and got stuck at the acceleration test stage. Falcon booted without problem with disabled booster, but I got only black screen with booster enabled. During reading of various acceleration fitting woes on this fine forum, many if not all pointed out that this could be a Falcon clock problem I finally fitted in NvRAM and a clock fix I bought a while ago from Centuriontech (since I'm from EU) and lo and behold, it works now.

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We have acceleration! Phase one and two seems to be a success, Falcon acceleration tested @40MHz.

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While at it, I also replaced C7 1uF with 22uF cap and a big 4700uF with a much lower ESR cap.

[Badwolf]

We have acceleration! Phase one and two seems to be a success, Falcon acceleration tested @40MHz.

Well done! Congratulations on getting this far.

:girldance:

Also thanks for the (AFAIK) first direct evidence of the clock patch making a material difference to the functioning of a DFB1. :thumbup:

BW

[flegmatik]

This is it for now, apparently I forgot to order flash. Also, my FPU turned out not to be 40MHz capable, it crashed FPUTEST right at the start.

This was my idea how to run CPU and FPU with one oscillator.

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I removed the bodge wire and populated R18, 20MHz will do for now. I also stuck a large passive cooler on CPU, it is overclocked afteral.

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And the result

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[Badwolf]

This is it for now, apparently I forgot to order flash. Also, my FPU turned out not to be 40MHz capable, it crashed FPUTEST right at the start.

Do you have an FPU on the main motherboard too? I'm not sure it's documented properly, but I think you ought to remove that.

Could be what's causing the problems at higher speeds.

BW

[flegmatik]

No, I moved FPU from main board to accelerator. I bought 40MHz capable CPU and FPU couple of months ago from Amigastore (since I'm from EU), but it is possible I mixed FPU's with my Mega STE. I'll have to check which FPU ended where :D

Anyway, it seems that everything is running very stable.

[Steve]

@flegmatik please see Exxos previous FPU benchmark results: https://www.exxosforum.co.uk/atari/last/FPU/index.htm

You'll see between 32mhz and 50mhz only shaves off 2 seconds, and anything past that is totally useless. So if you get any speed between 32mhz and 50mhz stable I think that is perfectly fine.

Also there is a case for not wanting 50mhz. For instance, at 50mhz many FPUs will be capable of rendering a fractal. But when closely inspected using DML's FPU test program (which runs mathematical equations on the FPU and reports whether the result is good or bad) often chips which you think present good, fail certain equations.

So it is in my sincere opinion that running an FPU at 50mhz is really pushing those chips to breaking point, and backing it off to 40mhz or 32mhz is wise.

[flegmatik]

Great, thanks @Steve!
My intention here is a budget accelerator, that's why 64MB fast RAM, 40MHz CPU and ideally, FPU. I'll test FPU at 32MHz, perhaps it will work, if not, it will be fine at 20MHz until something better comes along.

[flegmatik]

Final version CPU and FPU @32MHz, 64MB TT RAM and 8Mbit Flash memory

Decided on 32MHz because of three reasons:
- FPU works at 32MHz (all good with Fputest)
- CPU doesn't get crazy hot (plastic 68030)
- I feel it's fast enough (for now)

This time I've fitted bodge wire from CPU oscillator to FTP on the back side of the board.

It works like a charm.

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[Steve]

Very nice!