Atari TT - FPU Overclock

[Icky]

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 (1.31 MiB) Viewed 1216 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 (1.32 MiB) Viewed 1216 times

IMG_2822.png (1.32 MiB) Viewed 1216 times

I will post benchmarks of stock and overclocked FPU shortly.

[exxos]

[Steve]

Very cool!

[tuxie]

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

[crashman]

Very nice patch!
I have to try that!

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

Thanks!

[Icky]

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

[crashman]

Thanks a lot!!!

[Icky]

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

1A396258-8366-4F36-B333-D32B0E379728.png (4.36 KiB) Viewed 1170 times

[Icky]

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 (1.46 MiB) Viewed 743 times

[Steve]

Was just re-reading your post again and you mentioned thinking about changing the fpu chip to a 40mhz varient, but I don't think you mention whether you did or not. Did you?