DFB1r5 Design Review Thread

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Badwolf
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DFB1r5 Design Review Thread

Post by Badwolf »

Afternoon all.

I'm about ready to push the button on PCB production for DFB1r5, but since revision 4 made the project functionally complete (albeit with some bodge wires and trace cutting needed), I think it's time to open up the hardware source to the collective wisdom of the board so, with luck, there doesn't need to be a revision 6.

To that end, below is a PDF render of the schematic and the Kicad files have been published on my GitHub: https://github.com/dh219/DFB

Should anyone with hardware design experience wish to take a look and spots any obvious brainfarts on my part, please do speak up. I'm hoping to press go on the order towards the end of this week coming (week ending 21st January 2022).

For example on my last revision, I put a top byte line on the second from top byte of my RAM buffers, and vice versa. I also wired up A0 on the FPU instead of tying it to VCC.

These are the sorts of things I'm hoping to avoid by opening the source early.

Changes to this from the last revision (see https://www.exxosforum.co.uk/forum/viewt ... =29&t=4532) include:-
  • FCx correctly joined;
  • Optional pullups on the bus arb lines & reset;
  • Optional SMD resistors on clocks;
  • Declutter FB5 on CPLD;
  • Second optional OSC for FPU;
  • Cuttable BGI/BGO bridge;
  • Corrected FPU lines;
  • Corrected RAM data lines;
  • Reordered ROM lines;
  • Reduced number of fixed pull-ups: direct to VCC where possible.
I very much suspect I'm going to get a few 'Can you add X' type comments. The answer -- unless it's a truly stunning idea achievable with five minutes work -- is no. I'll remind you the original design goals are:
  • Be a plug-in board requiring no soldering on the Falcon;
  • Increase available RAM beyond the 14MB the stock Falcon can be expanded to;
  • Be low cost;
  • Provide some acceleration;
  • Allow the PSU to remain in the case;
  • Be open source.
But I do welcome any bug fix suggestions as the aim for this revision is zero bodge wires.

Thanks,

BW.
Attachments
DFB1r5_RC1_schematic.pdf
(929.27 KiB) Downloaded 91 times
DFB1 Open source 50MHz 030 and TT-RAM accelerator for the Falcon
DSTB1 Open source 16Mhz 68k and AltRAM accelerator for the ST
Smalliermouse ST-optimised USB mouse adapter based on SmallyMouse2
FrontBench The Frontier: Elite 2 intro as a benchmark
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DoG
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Re: DFB1r5 Design Review Thread

Post by DoG »

Thank you. Very much appreciated!
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exxos
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Re: DFB1r5 Design Review Thread

Post by exxos »

I can take a look on Monday if you like, or I can not look if you prefer ;)
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Badwolf
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Re: DFB1r5 Design Review Thread

Post by Badwolf »

exxos wrote: Sun Jan 16, 2022 12:08 am I can take a look on Monday if you like, or I can not look if you prefer ;)
Cheers. Don't spend an age, but if you can see an obvious balls up before I press order I'd rather know about it than not!

I even have a small bingo card here already for 'things that I think Exxos will hit me about the head and chest for doing'.

I've already crossed off one of them -- I'm that confident in my prediction for that one and have been tying to decide if I'll give in or not. ;-)

BW
DFB1 Open source 50MHz 030 and TT-RAM accelerator for the Falcon
DSTB1 Open source 16Mhz 68k and AltRAM accelerator for the ST
Smalliermouse ST-optimised USB mouse adapter based on SmallyMouse2
FrontBench The Frontier: Elite 2 intro as a benchmark
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Re: DFB1r5 Design Review Thread

Post by exxos »

Badwolf wrote: Sun Jan 16, 2022 4:03 pm I even have a small bingo card here already for 'things that I think Exxos will hit me about the head and chest for doing'.

I've already crossed off one of them -- I'm that confident in my prediction for that one and have been tying to decide if I'll give in or not. ;-)
:lolbig: :bravo:
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https://www.exxosforum.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
Just because a lot of people agree on something, doesn't make it a fact. ~exxos ~
People should find solutions to problems, not find problems with solutions.
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Re: DFB1r5 Design Review Thread

Post by exxos »

Just got home, had a quick look at the PCB layout, I don't see any of my "pet hates" on there :thumbup:
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https://www.exxosforum.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
Just because a lot of people agree on something, doesn't make it a fact. ~exxos ~
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Re: DFB1r5 Design Review Thread

Post by Badwolf »

exxos wrote: Sun Jan 16, 2022 10:10 pm Just got home, had a quick look at the PCB layout, I don't see any of my "pet hates" on there :thumbup:
Ta!

Although it's an absence of things that I had you down for. ;)

BW
DFB1 Open source 50MHz 030 and TT-RAM accelerator for the Falcon
DSTB1 Open source 16Mhz 68k and AltRAM accelerator for the ST
Smalliermouse ST-optimised USB mouse adapter based on SmallyMouse2
FrontBench The Frontier: Elite 2 intro as a benchmark
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Re: DFB1r5 Design Review Thread

Post by exxos »

Badwolf wrote: Mon Jan 17, 2022 1:20 pm Although it's an absence of things that I had you down for. ;)
I assume you're talking about the bus pullups ?
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https://www.exxosforum.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
Just because a lot of people agree on something, doesn't make it a fact. ~exxos ~
People should find solutions to problems, not find problems with solutions.
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Re: DFB1r5 Design Review Thread

Post by Badwolf »

exxos wrote: Mon Jan 17, 2022 1:29 pm
Badwolf wrote: Mon Jan 17, 2022 1:20 pm Although it's an absence of things that I had you down for. ;)
I assume you're talking about the bus pullups ?
Aye. :P

And that's the one I was mulling over whether to acquiesce to and try to squeeze some optional footprints on somewhere. I think doing the data bus wouldn't be too bad as I could move the lines coming out of the bottom header connector to the top layer, place the footprints underneath and then drop all the lines down with vias to meet the tracks further along, but the address lines would be problematic, I think.

It's a mess up the north side of the board!

BW

Screenshot 2022-01-17 at 14.57.26.png
Screenshot 2022-01-17 at 14.57.26.png (210.44 KiB) Viewed 2320 times
Screenshot 2022-01-17 at 14.52.14.png
Screenshot 2022-01-17 at 14.52.14.png (241.1 KiB) Viewed 2320 times
DFB1 Open source 50MHz 030 and TT-RAM accelerator for the Falcon
DSTB1 Open source 16Mhz 68k and AltRAM accelerator for the ST
Smalliermouse ST-optimised USB mouse adapter based on SmallyMouse2
FrontBench The Frontier: Elite 2 intro as a benchmark
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Re: DFB1r5 Design Review Thread

Post by exxos »

Badwolf wrote: Mon Jan 17, 2022 2:51 pm
exxos wrote: Mon Jan 17, 2022 1:29 pm I assume you're talking about the bus pullups ?
Aye. :P

And that's the one I was mulling over whether to acquiesce to and try to squeeze some optional footprints on somewhere. I think doing the data bus wouldn't be too bad as I could move the lines coming out of the bottom header connector to the top layer, place the footprints underneath and then drop all the lines down with vias to meet the tracks further along, but the address lines would be problematic, I think.
Well, I cannot really tell you to add them or not because I have not had much dealings with the Falcon. Of course I can only make suggestions based on all the chaos I have seen on the ST line thusfar. Atari definitely had a trend of consistently screwing things up across various machines though. I have dealt with enough ST's over the years to know that the pullups are just mandatory on those machines. They were barely functioning out of the factory never mind adding in 30 years of maturity on top of that.

The way to decide is to just simply measure the rise and fall times of the bus and see if the extra pullups making any real-world difference or not.. On the ST it was spanning like 200ns rise times in some cases. I somehow think a 060 CPU running 100mhz would not work with those timings. So I would generally assume that the Falcon has better rise times (maybe 20ns ?) "out of the box" Otherwise the CT60 wouldn't work. OTOH the chips may have some internal pullups as a option anyway.. Or they may not be that much loading the Falcon bus.. I really have not looked into it all.

So in this instance, I will forgive you if you do not want to add them ;)
https://www.exxosforum.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxosforum.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
Just because a lot of people agree on something, doesn't make it a fact. ~exxos ~
People should find solutions to problems, not find problems with solutions.
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