exxos's Atari, Amiga & retro forum

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 https://www.exxosforum.co.uk/forum/viewt ... 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.


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.


I will post benchmarks of stock and overclocked FPU shortly.

Very cool!

Very nice patch!
I have to try that!

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

Thanks!

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

Thanks a lot!!!

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

Just to add the Gembench mark is around 100% for stock FPU but using the overclock comes out at 245%

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?

Steve wrote: ↑Thu Jan 03, 2019 11:45 am 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?

For the life of me I could not remember. I actually got my TT all back together again at the end of last year.

Its a bit packed in Gigafile, SD-IDE connected to Thunder board, USB poking out the back connected to Lightning board, 10MB ST-RAM board and Mach64 VGA card at the back.


Just tried to take a look and the FPU is tucked away under the VME board but I managed to get my phone under enough to take a pic and it is the 40MHz variant.