DFB1r4 design discussion thread

General discussions or ideas about hardware.
Badwolf
Posts: 454
Joined: Tue Nov 19, 2019 12:09 pm

DFB1r4 design discussion thread

Post by Badwolf » Fri Aug 06, 2021 12:39 pm

I'm turning my attention to the next revision of my DFB1 Falcon Booster (https://github.com/dh219/DFB/wiki). I'm hoping this one will be the final spin so the aims beyond the last model are:-
  • Fit in a footprint that will allow the keyboard and PSU to be fitted and the case closed;
  • Switch to 4 layer board;
  • Work reliably at 50MHz (ideally driving the RAM at 100MHz, like the TF536).
But I'm also considering going from one CPLD to two for more flexibility and perhaps allow me to expose some registers.

One XC95288XL 144-pin CPLD (currently in use on my first, heavily modified, rev3 board which runs at 50MHz) currently costs around £20. I've managed to squeeze a cut-down firmware into an XC95144XL (£10) for my second rev3 (unmodified & can only handle 40MHz -- poor clock lines?). But this is extremely restricted.

To me one £10 144 CPLD to handle SDRAM and address decoding and one £5 72 CPLD to handle the bus and perhaps service a register or two seems like better value in terms of capability and risk (blowing any one up is cheaper!) but it does add complexity.

What do you guys think? Is keeping the two playing nicely together harder than I imagine?

Cheers,

BW.
Falcdate Use the internet to work around dead Falcon NVRAM battery
Smalliermouse ST-optimised USB mouse adapter based on SmallyMouse2
DFB External 030 and AltRAM for the Falcon (under development)

Badwolf
Posts: 454
Joined: Tue Nov 19, 2019 12:09 pm

Re: DFB1r4 design discussion thread

Post by Badwolf » Fri Aug 06, 2021 2:31 pm

It would be nice to fit an FPU on as well, but space is a bit tight, I think.

dfb1r4_layout_considerations.png
dfb1r4_layout_considerations.png (57.34 KiB) Viewed 616 times

Yellow is maximum extend of board outline I want to run to. Ideally cut off at the dashed line as anything below that has to be very low profile. The CPU needs to be as near to the top of the board as possible for under-keyboard clearance if using a socket.

BW
Falcdate Use the internet to work around dead Falcon NVRAM battery
Smalliermouse ST-optimised USB mouse adapter based on SmallyMouse2
DFB External 030 and AltRAM for the Falcon (under development)

User avatar
frank.lukas
Posts: 328
Joined: Fri Jan 19, 2018 11:52 am

Re: DFB1r4 design discussion thread

Post by frank.lukas » Fri Aug 06, 2021 5:13 pm

ideas ...

- the FPU could also be fitted on the back of the board, as well as other things as well.
- adapter board between the CPU socket and the CPU with the FPU on it.

User avatar
exxos
Site Admin
Site Admin
Posts: 15799
Joined: Wed Aug 16, 2017 11:19 pm
Location: UK
YouTube: exxosuk
Contact:

Re: DFB1r4 design discussion thread

Post by exxos » Fri Aug 06, 2021 5:45 pm

Does it really need a FPU if the Falcon has one anyway.. simple to overclock it anyway.
https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.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 ~

Badwolf
Posts: 454
Joined: Tue Nov 19, 2019 12:09 pm

Re: DFB1r4 design discussion thread

Post by Badwolf » Fri Aug 06, 2021 9:24 pm

@exxos: The Falcon's FPU's DS line isn't actually wired to the expansion port (hence the jump wire here):

dfb1r3b2_800px.jpg
dfb1r3b2_800px.jpg (262.22 KiB) Viewed 567 times
Plus it's only 16 bit. Not that I know if it makes a big difference.

The CT2 managed to get an FPU on there although it does look like the CPU heatsink overlaps the hard drive bracket, so that might be cheating a bit.

ct2b.png
ct2b.png (537.44 KiB) Viewed 567 times

@frank.lukas, yeah a PLCC FPU is slim enough to fit on the back but the only real place with clearance is where I have earmarked for the CPU (which is annoyingly through hole!). I don't think an adapter board will work either as vertical space is the limiting factor with the CPU+socket setup already. I might be able to do something with flat flex and a daughterboard, but I'm going to be ambitious ;-)

I have had another measure about and I reckon there's another 12-15 mm I could extend to the left -- out over the enhanced joystick ports, providing it's top side only. I think I can squeeze another 6mm on the right hand side too. That may not be much use, though.

Screenshot 2021-08-06 at 21.08.30.png
Screenshot 2021-08-06 at 21.08.30.png (52.31 KiB) Viewed 567 times

Perhaps I should stick with one CPLD just for board space and routeing efficiency?!

BW
Falcdate Use the internet to work around dead Falcon NVRAM battery
Smalliermouse ST-optimised USB mouse adapter based on SmallyMouse2
DFB External 030 and AltRAM for the Falcon (under development)

User avatar
exxos
Site Admin
Site Admin
Posts: 15799
Joined: Wed Aug 16, 2017 11:19 pm
Location: UK
YouTube: exxosuk
Contact:

Re: DFB1r4 design discussion thread

Post by exxos » Fri Aug 06, 2021 9:36 pm

Badwolf wrote:
Fri Aug 06, 2021 9:24 pm
@exxos: The Falcon's FPU's DS line isn't actually wired to the expansion port (hence the jump wire here):
Plus it's only 16 bit. Not that I know if it makes a big difference.
Never thought of that.. don't know much about the FPU , it being 16bit or 32bit.. IMHO leave it off, save some trouble.. can always do a new design in the future.

Badwolf wrote:
Fri Aug 06, 2021 9:24 pm
Perhaps I should stick with one CPLD just for board space and routing efficiency?!
Again IMHO, 1 chips easier to solder than 2... If 1 chip can be used then that's what I would go for. Less routing as well.. Plus a lot of pins like the address bus could end up being duplicated which just making it more complex than it needs to be.
https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.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 ~

Badwolf
Posts: 454
Joined: Tue Nov 19, 2019 12:09 pm

Re: DFB1r4 design discussion thread

Post by Badwolf » Fri Aug 06, 2021 10:37 pm

exxos wrote:
Fri Aug 06, 2021 9:36 pm
Never thought of that.. don't know much about the FPU , it being 16bit or 32bit.. IMHO leave it off, save some trouble.. can always do a new design in the future.
Mmm. Was hoping to make this one as feature complete as possible and only respin for corrections. Perhaps I'll start routeing and see how it looks.
Again IMHO, 1 chips easier to solder than 2... If 1 chip can be used then that's what I would go for. Less routing as well.. Plus a lot of pins like the address bus could end up being duplicated which just making it more complex than it needs to be.
I'm just being a cheapskate. I'm hard up against the limit of a 144 and a 144 and a 72 (or even a smaller footprint 144) are cheaper than a 288.

Blown up too many, I suppose :lol:

Two chips does give more flexibility for optimising the SDRAM controller, though. That thing accounts for 2/3rds the damned logic and is the limiting factor on everything.

You're probably right on that one, though. I'd have to add a load of logic for them to talk to each other and there are a handful (~8-10) of shared pins.

Cheers,

BW
Falcdate Use the internet to work around dead Falcon NVRAM battery
Smalliermouse ST-optimised USB mouse adapter based on SmallyMouse2
DFB External 030 and AltRAM for the Falcon (under development)

Badwolf
Posts: 454
Joined: Tue Nov 19, 2019 12:09 pm

Re: DFB1r4 design discussion thread

Post by Badwolf » Tue Aug 10, 2021 4:06 pm

Bit of a work in progress screenie:

Screenshot 2021-08-10 at 16.01.04.png
Screenshot 2021-08-10 at 16.01.04.png (482.05 KiB) Viewed 470 times

Placing my CPU right at the edge of the board then trying to fan it out... Grr! :lol:

BW
Falcdate Use the internet to work around dead Falcon NVRAM battery
Smalliermouse ST-optimised USB mouse adapter based on SmallyMouse2
DFB External 030 and AltRAM for the Falcon (under development)

User avatar
exxos
Site Admin
Site Admin
Posts: 15799
Joined: Wed Aug 16, 2017 11:19 pm
Location: UK
YouTube: exxosuk
Contact:

Re: DFB1r4 design discussion thread

Post by exxos » Tue Aug 10, 2021 4:10 pm

Badwolf wrote:
Tue Aug 10, 2021 4:06 pm
Placing my CPU right at the edge of the board then trying to fan it out... Grr! :lol:
Angle it ;)
https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.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 ~

Badwolf
Posts: 454
Joined: Tue Nov 19, 2019 12:09 pm

Re: DFB1r4 design discussion thread

Post by Badwolf » Tue Aug 10, 2021 4:38 pm

exxos wrote:
Tue Aug 10, 2021 4:10 pm
Badwolf wrote:
Tue Aug 10, 2021 4:06 pm
Placing my CPU right at the edge of the board then trying to fan it out... Grr! :lol:
Angle it ;)
I'm trying to get it as far north on the board as possible for keyboard clearance.

Board+Socket+CPU is tight and I'd like to be able to fit a heatsink.

It'll fit. Damnit, it'll fit. :lol:

BW
Falcdate Use the internet to work around dead Falcon NVRAM battery
Smalliermouse ST-optimised USB mouse adapter based on SmallyMouse2
DFB External 030 and AltRAM for the Falcon (under development)

Post Reply

Return to “HARDWARE DISCUSSIONS”