Overclocking the GVP G-Force 030
This popular A2000 accelerator card was made by GVP and contained either a 25MHz 68EC30, a 40MHz 68EC030, or a 50MHz 68030. All versions of this card also contained a SCSI controller and a RAM expansion, using custom 64 pin "GVP SIMMs". This board is remarkably similar to the GVP "Combo" accelerator which can be found elsewhere on this site. However, there are a few differences, mainly in the way the FPU is clocked, which in the case of the G-Force has the facility to be clocked separately if desired. The FPU is also removable, being fitted in a PGA socket.. Some versions of the G-Force were fitted with a metal shield over the CPU area, which will need to be removed to gain access. The board I had did not have this shield, and was the 40MHz 68EC030 version. The FPU was also a 40MHz device.
This board has provision for two standard 14-pin form factor oscillator modules as can be seen in the top left of the above picture. In the upper position was an empty socket for the FPU oscillator and in the bottom position a 40MHz oscillator was soldered into place. The board was jumpered to provide 40MHz from the CPU oscillator to the FPU. The first step in overclocking the board is to carefully remove the soldered in CPU oscillator. Once removed, a good quality 14-pin IC socket with all pins removed except pins 1,7,8,&14 can be soldered in it's place. Note that there are no extra holes on the PCB to allow the use of 8-pin size oscillators. The new oscillator was plugged in, making sure that it is the correct way around, with the dot on the corner facing towards the memory SIMMs. As always, incorrect orientation of the oscillator will result in it's prompt destruction!
At first I tried a 50MHz oscillator, but the system would not boot at all. A 48MHz oscillator also gave no results. The next frequency I had was 44.9Mhz, and this worked perfectly. There are a number of jumpers on the board which are set in accordance with the CPU frequency. I found that to ensure reliability, I had to set these for 50MHz (see below). The jumper controlling the FPU was then changed and a 60MHz oscillator fitted. The FPU didn't like this - the system hung whenever the FPU was used. I then tried a 55.5MHz oscillator, however, the "BeachBall" in AIBB was horribly distorted. Using a 54MHz oscillator resulted in correct and reliable operation.
Like the GVP 'Combo', this board uses programmed GAL chips for part of its logic, and GVP programmed these to suit the CPU speed used. Replacing these GALs should allow this board to operate at 50MHz, however, these GALs are unobtanium, and unfortunately, GVP set the protection bit when programming them, so it is not possible to copy them onto blank GAL chips.
The socketed 68030 does not seem to overheat, which is just as well as there is very little room to fit a heatsink due to the close proximity of the floppy drive bracket.
Jumper Settings.
Due to the fact that many different GVP 030 accelerator models for the A2000 look remarkably alike, it is most important that you check to make sure yours looks exactly like the one above before you start playing with the jumper settings! Note that some boards have a metal cover over the CPU & FPU area, however they are otherwise identical to the one on this page. These jumper settings DO NOT apply to the GVP "Combo" board described elswhere on this site.
Note: Jumper J12 controls where the memory is located. With the jumper open, all of it is located outside the ZII address range. With the jumper closed, the first 8MB (the first two banks) are located within the ZII address range.
Usage with OS 3.9.
In certain cases, sometimes if 16-bit Zorro II memory is present, a small improvement in SCSI transfer performance can be achieved by altering the Setpatch command in the startup-sequence. The command line should look like this: C:SetPatch QUIET AVOIDMEMFKICKFORPATCHES After saving the changes, switch the Amiga off then back on. This can be tried even if you don't overclock your board. It may or may not work on other GVP accelerators, but there isn't any harm in trying.
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Introduced 23rd June 2002. Updated 20th May 2023. Version 1.1