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. My board is the 40 MHz version, and is the one featured here.

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.

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 each the different speed boards in their range. Unfortunately, as the protection bit was set in these GALs, it is not possible to copy them into new ones for 50 MHz.

Much later, I found the files that allowed me to burn my own 50Mhz GAL chips. They can be found on this site (translated from the orginal Italian) 50MHz Combo This site also contains instructions on how to convert the original GVP PAL files on the site to GAL files that are suitable for the more modern and easier to obtain and program GAL chips. It should also be possible to upgrade 25MHz and 33MHz versions by replacing the PALs in them with the 50MHz GALs. As I don't have a 25 or 33MHz board, I cannot test this.

As it turned out, my 40 MHz Combo card only had a single different GAL compared the the 50 MHz version, which was U36. The 40MHz U36 had a checksum of 90C4, the 50MHz version was 90C6. I programmed a new U36 and installed it. Unfortunately I got no improvement. Some sources did say that the 40MHz 90C4 was also suitable at 50 MHz, but obviously not for me. I carefully inspected my board and compared it to pictures of genuine 50MHz versions, and mine was identical in every way. After some thought, I decided to measure the 5V supply on my board (a convenient place to do this is on the oscillator pins). I got 4.8V. Slightly low, but perfectly fine, and well within specifications. Just for fun, I connected an additional 5V supply, taken from a spare drive connector directly to the oscillator 5V pins, bringing the voltage up to a full 5V. This time I was able to get the board to work at 46MHz, though it was slightly unreliable after it warmed up.

My A2000 currently has a 3.2.2 Kickstart ROM in it. On previous attempts at overclocking it had a 3.1 Kickstart. I put a 3.1 ROM back in, and this time it booted fine at 50MHz. I even got it to work OK at 54MHz. Disconnecting the additional 5V supply I had added caused the same failures I had on my original tests many years ago. So I was a victim of a classic case of two separate faults masking each other. The slightly low 5V causing failure, and OS 3.2 causing failure even with a full 5V. I think there is still something odd going on, 4.8V is well within tolerance levels. It shouldn't cause problems. As for OS3.2 is there a bug somewhere? Are there any 50MHz Combo users running OS3.2 successfully?

Literally minutes after I updated this site, I received confirmation from a good source that the 50MHz Combo card does work with OS 3.2, so clearly I have something odd going on. With that in mind, it is quite likely that there is a good chance other 40 MHz boards will operate at 50 MHz. In any case, I had already decided to return my machine to 44.9MHz. During my tests, I had replaced all the original PAL chips with GAL chips, and I kept those in as they ran cooler.

Due to GVP having a rather sparse description of the jumper settings, with most listed simply as 'reserved', I have decided to include an expanded version of the settings I found below. 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 single oscillator "Combo" board described elswhere on this site.

Jumper	GVP name	Description	Settings	Default (40MHz)
J2	68030 enable	Select 68030 or motherboard CPU	Open = motherboard CPU, closed = 68030	Closed
J3	MMU	68030/68EC030 selection	Open = 68030, closed = 68EC030	Open
J4	Reserved	Memory controller	Closed for all versions	Closed
J5	Reserved	Memory controller	40MHz = open, 25 & 50Mhz = closed	Open
J6	Reserved	Memory controller	25MHz = open, 40 & 50MHz = closed	Closed
J7	Reserved	Memory controller	Open for all versions	Open
J8	Omni ROM (AT/SCSI)	Select SCSI ROM type	AT/SCSI (default), SCSI = Closed	Open
J9	Auto Boot	Enable/disable SCSI ROM	Closed=enabled, open = disabled	Closed
J10	Reserved	Unimplemented memory option		Open
J11	Reserved	For original German A2000	Open=Rev4 and later, closed = German version	Open
J12	Memory mapping	Select ZII or extended memory map	Closed = Banks 1 & 2 in ZII space, open = extended	Open
J13	Reserved	Unimplemented SIMM32 option		Open
J14	SCSI drive	Presence or absence of SCSI drive	Closed = no drive, open = drive present	Closed
J15	Reserved	Internal test option		Open
CN7	Reserved	Memory wait state	1 & 2 jumpered = on, 2 & 3 jumpered = off (25MHz)	1 & 2 jumpered
CN8	Reserved	Memory clock settings	1 & 2 = 40 & 50MHz, 2 & 3 = 25Mhz	1 & 2 jumpered
CN14	Reserved	DPRC clock source	2 & 3 = 7MHz, 1 & 2 = 14 MHz	2 & 3 jumpered
CN15	Reserved	SCSI controller clock	2 & 3 = 7 MHz, 1 & 2 = 14 MHz	1 & 2 jumpered
CN16	FPU clock source	choose CPU or separate clock	1 & 2 = separate clock, 2 & 3 = CPU clock	1 & 2 jumpered
LED	for SCSI activity light

Note: Later (Rev4) boards contain additional jumpers (J16 - DTACK pullup for old motherbards, and CN17 - Undocumented clock option)

Jumper J8 selects SCSI ROM type. Do not confuse the GVP name 'Omni ROM' with the 'omniscsi.device' as used in the third party 'Guru ROM'

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. With the jumper open, the GVP SCSI ROM contains memory control routines that enables the RAM, otherwise you will need to use 'Addmem"

Jumper CN7 controls memory wait states, and GVP advises this be set 'on' for speeds over 25 MHz. I think they were thinking of a worst case scenario where 70 or 80 nS RAM is used. My RAM is all 60nS, and I achieved reliable operation at all speeds with the wait state off.

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 4th February 2024. Version 1.3