Atari TT - FPU Overclock

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Icky
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Atari TT - FPU Overclock

Post by Icky » Wed Apr 04, 2018 10:00 pm

Over the Easter weekend I decided to overclock the FPU in the Atari TT. I had seen several areas on the web that discussed changing the clock on the FPU from its stock 32MHz to 40MHz or 48 MHz. In fact there is a mention from Tuxie on this thread about it viewtopic.php?f=29&t=487.

I had a think and thought about firstly updating the FPU chip from the stock 33MHz to a 40MHz one from Exxos' store. I know that the original one can be over clocked but I just want to put the least stress on my precious TT. I also wanted to make it as intrusive as possible and went about trying out the 40MHz and 48MHz to test and plumped with the 48MHz as the system handled it under stress testing.

To make this intrusive I just wanted to be able to plug this in without any soldering to the board. Initially I created this simple XTAL, DIL and leads setup.

Below shows the individual components and the one with leads is the 48MHz crystal in the dil socket wired and wrapped in insulating tape.

IMG_2802.png
IMG_2802.png (1.31 MiB) Viewed 772 times

What makes this a plug and play solution is the circuit can be plugged into the +5v and GND pins on the top of the Storm memory card and then the output lead to the middle pin on the FPU clock selection jumper.

IMG_2821.png
IMG_2821.png (1.32 MiB) Viewed 772 times
IMG_2822.png
IMG_2822.png (1.32 MiB) Viewed 772 times

I will post benchmarks of stock and overclocked FPU shortly.

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exxos
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Re: Atari TT - FPU Overclock

Post by exxos » Wed Apr 04, 2018 10:06 pm

:bravo: :coolpics:
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https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
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Re: Atari TT - FPU Overclock

Post by Steve » Thu Apr 05, 2018 3:10 am

Very cool!

tuxie
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Re: Atari TT - FPU Overclock

Post by tuxie » Thu Apr 05, 2018 8:14 am

Great Work,

i soldered a OSC onto one other IC and plugged a short wire into the middle pin like you.
48Mhz is a good size.

I am glad to see the Thunder Storm in other TT´s :D

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crashman
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Re: Atari TT - FPU Overclock

Post by crashman » Thu Apr 05, 2018 11:24 am

Very nice patch!
I have to try that!

The 4th pin on the Crystal is left alone? or connected to what?

Thanks!

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Icky
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Re: Atari TT - FPU Overclock

Post by Icky » Thu Apr 05, 2018 11:49 am

crashman wrote:
Thu Apr 05, 2018 11:24 am
Very nice patch!
I have to try that!

The 4th pin on the Crystal is left alone? or connected to what?

Thanks!
Not connected. It’s as simple as +5V, GND & Clock out

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crashman
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Re: Atari TT - FPU Overclock

Post by crashman » Thu Apr 05, 2018 1:21 pm

Thanks a lot!!!

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Icky
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Re: Atari TT - FPU Overclock

Post by Icky » Thu Apr 05, 2018 6:44 pm

Just for reference this is the pin out diagram I used to connect the crystal up with

1A396258-8366-4F36-B333-D32B0E379728.png
1A396258-8366-4F36-B333-D32B0E379728.png (4.36 KiB) Viewed 726 times

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Re: Atari TT - FPU Overclock

Post by Icky » Sat Aug 11, 2018 12:40 am

Just to add the Gembench mark is around 100% for stock FPU but using the overclock comes out at 245%
GemBench - TT ST Med FPU Overclocked.png
GemBench - TT ST Med FPU Overclocked.png (1.46 MiB) Viewed 299 times

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