Overclocking the GVP 030 Combo - dual oscillator version.

This popular A2000 accelerator card was made by GVP and sold under a confusing variety of names and models. They 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". Some boards have the CPU and FPU soldered directly to the PCB, with a single oscillator driving both CPU and FPU. Some were also fitted with a metal shield over the CPU area, which will need to be removed to gain access. The board I have was labelled 'version 3' and did not have this shield, It has a 40MHz 68EC030 with sockets for the CPU and FPU. There is also a version 4, but I don't know if this difference warranted GVP selling it under a different name. The version number can be found printed into the PCB, along the edge just above the soldered in RAM chips and to the left of the SCSI connector.

This board has provision for two standard 14-pin 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. 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. There are a number of jumpers on the board which are set in accordance with the CPU frequency. I found that to ensure best reliability and speed, I had to set these as shown in the table below.

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.

A little later, I obtained a genuine 50MHz 68030 and tried again to clock this board at 50 MHz. I got exactly the same results as with the 40MHz CPU. This indicates that there is some limitation in the 40MHz version of this board that prevents operation at 50MHz. It seems that GVP used differently programmed GAL chips on the 50MHz boards. Unfortunately, as the protection bit was set in these GALs, it is not possible to copy them into new ones for 50 MHz.

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 are only for version 3 of this board and DO NOT apply to the GVP "Combo" board described elswhere on this site.

JumperOpen PositionClosed PositionDefault (40MHz)Overclocked
J2CPU DisabledCPU EnabledClosedClosed
J3MMU Enabled (68030)MMU Disabled (68EC030)OpenOpen
J5CPU=40MHzCPU=25MHz or 50MHzOpenOpen
J6CPU=25MHzCPU=40MHz or 50MHzClosedClosed
J8Omni ROM (either SCSI or IDE)SCSI ROMOpenOpen
J9Auto Boot disabledAuto boot enabledClosedClosed
J12All memory extendedMemory banks 1& 2 auto configClosedOpen
J14SCSI drive presentSCSI drive absentClosedClosed
JumperPins 1 & 2Pins 2 & 3DefaultOverclocked
CN7ReservedReservedPins 1&2 jumperedPins 1&2 jumpered
CN8Memory wait state (50Mhz)No memory wait state (25-40 Mhz)Pins 1&2 jumperedPins 2&3 jumpered
CN14ReservedReservedPins 2&3 jumperedPins 2&3 jumpered
CN15SCSI 14MHzSCSI 7MHzPins 2&3 jumperedPins 1&2 jumpered
CN16Separate FPU clockFPU uses CPU clockPins 2&3 jumperedPins 1&2 jumpered
LEDfor SCSI activity light

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. Be aware that having this memory in the ZII range can cause clashes with many Zorro cards containing memory, including RAM expansions, bridgeboards and many graphics cards.

Jumper CN15 controls the clock speed for the SCSI controller chip. For some reason it is defaulted to 7Mhz, even though the SCSI chip is designed for 14MHz. Changing it as shown above will give a big increase in SCSI speed.

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 June 23rd 2002. Updated 20th May 2023. Version 1.2