DIY Fpu Unit for STFM

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tcat
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Re: DIY Fpu Unit for STFM - possible?

Postby tcat » Fri Aug 02, 2019 10:23 am

Hi,

While working on eschema, I spoted that AS signal in PLCC pinout is not inverted, while in PGA pinout has /AS inverted.
As I have PLCC package I need to know, is this a printing mistake or a fact????

Many thanks in advance
Tomas

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Re: DIY Fpu Unit for STFM - possible?

Postby SteveBagley » Fri Aug 02, 2019 6:01 pm

Have you thought about making this as a board that plugs into the ROM sockets and the ROM sockets plug into? You can pick up a lot of the signals needed from there (A1—A17, D0-D15), which would mean you'd have to pick up a few signals from elsewhere… You'd also be able to decode TOS 2.06 and IDE on the same board very easily.

Steve

tcat
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Re: DIY Fpu Unit for STFM - possible?

Postby tcat » Fri Aug 02, 2019 6:50 pm

Hi Steve,

An interesting idea, need to study signals provided by ROM port (in ATARI reference book). I have made this eschema. ROM port might be a good option, but so far I thought to hook to CPU signals inside the machine. A few questions coming to my mind.

[a] where to source +5V and GND, inside STFM machine?
[b] will STFM power supply drive safely this board, in terms of extra current drawn by it?
[c] need to fit some smoothing and decoupling caps?
[d] in schematics I reused MC68000 symbol, as it conveniently provides singnals needed in one place. How to make an interfacing connector for the CPU?
There is some 3-4mm room above CPU inside the STFM case!

EDIT [d] CONN_SFP004 symbol added
EDIT [c] capacitors added
sfp004-eschema.png

Thanks for taking your interest.
Tomas
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tcat
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Re: DIY Fpu Unit for STFM - possible?

Postby tcat » Fri Aug 16, 2019 9:07 am

Hi,

I am now looking for motorola application note `AN947', the copy I have is missing appendices B and C.

Where to get the full document?

EDIT
Just found A,B,C appendices in the form of source text.

Many thanks
Tomas

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Re: DIY Fpu Unit for STFM - possible?

Postby tcat » Mon Sep 09, 2019 9:29 am

Hi,

I dare to share my PCB design, I have routed using `KiCad'. There is a capacitor close to VCC of each chip. Power comes through P2 connector, connector P1 should interface to CPU.

sfp004-pcb.png

Proper design with ground filled areas, so far beyond my capabilities, something I need to learn yet.

I need to connect P2 to common +5V rail inside ST machine, no idea yet where best to source, seeking advice. I though to use floppy power connector, is there a solid +5V and ground on it?

No idea it will work in the end, but this is how it may fit inside my STFM machine. P1 should connect to CPU pins using ribbons, at least that is the idea so far, but there is RP7 red component getting in the way on one CPU side. Inevitably the ribbon will partly cover CPU from top, any precautions here, to allow CPU dicipate its heat properly?

sfp004-mc68k-2.jpg

Many thanks in advance
Tomas
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tcat
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Re: DIY Fpu Unit for STFM - possible?

Postby tcat » Thu Sep 19, 2019 11:41 am

Hi,

I have only a simple `pistol' soldering iron, and I am not very skilfull with it. This is what I have , ICs populated in the sockets, VCC/GND sourced around PSU connector.

GEM-BENCH reports some 1400% on FPU math test, while SYSINFO reports NO-COPROCESSOR fitted.

What does it actually mean?

Many thanks
Thomas

sfp004-fitted2.JPG
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tcat
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Re: DIY Fpu Unit for STFM - possible?

Postby tcat » Fri Sep 20, 2019 10:03 am

Hi,

As my soldering is not very neat, I am no way sure I had it functional. I run this simple test that was coded by a German ATARI branch years ago.

Running FPU math test
https://qlforum.co.uk/download/file.php ... &mode=view
[cannot add 190K jpeg]

This may be an indication, it hopefully works?
Thomas

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Re: DIY Fpu Unit for STFM - possible?

Postby ThorstenOtto » Fri Sep 20, 2019 12:44 pm

tcat wrote:SYSINFO reports NO-COPROCESSOR fitted.

What does it actually mean?


There is an extra bit in the _FPU cookie that denotes the presence of a memory-mapped FPU. I guess sysinfo only checks for a "real" FPU.

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Re: DIY Fpu Unit for STFM - possible?

Postby tcat » Sat Sep 21, 2019 7:12 am

Hi Otto,

Cookies in a jar, I only heard of them.
Is it a piece of h/w or s/w, how can I support them on my TOS 1.04 (raibow)?

Many thanks
Tomas

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Re: DIY Fpu Unit for STFM - possible?

Postby ThorstenOtto » Sat Sep 21, 2019 9:49 am

It is software, basically a list of certain features/settings that is provided by the OS (or, in the case of TOS1.04, some resident program). You can find the description of the _FPU cookie at https://freemint.github.io/tos.hyp/en/b ... _2C_20_FPU

With TOS 1.04 you will have the problem that it does neither install that cookiejar, nor does it make entries for _CPU, _FPU etc.

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Re: DIY Fpu Unit for STFM - possible?

Postby troed » Sat Sep 21, 2019 10:39 am

It does indeed look like your FPU board is working. Nice work!


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