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Forums > C64 Coding > c128 test help needed to improve c128 emulation
2022-01-06 13:20

Registered: Sep 2007
Posts: 41
c128 test help needed to improve c128 emulation

Hiya all,

I am in the process of improving the MMU emulation in the x128 of the VICE project in collaboration with the author of the Z64K emulator and I need more test results from real c128 hardware.

People who are able and willing to test, please take the mmuswap-??.prg files from


When running the tests please make sure you do a hard reset / power cycles between tests.

When reporting the results I only need the test nr and the border color.

Thanks in advance to any-1 able and willing to test.
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2022-01-10 12:01

Registered: Jun 2011
Posts: 8
16 blue
18 white
19 light green
20 black
21 black
2022-01-10 15:15

Registered: Sep 2007
Posts: 41
Thank you all so much for running these tests, they have helped to make x128 and z64k to be more accurate compared to the real hardware.

For almost all of the tests we have an agreement in the results, the only tests we have a disagreement in the results are tests 06, 20 and 21.

These tests check if when both the zero page and stack page are mapped to the same normal ram page where the back translation goes, that normal ram page will show either the zero page or the stack page, not a mixture of both.

For the people who got a 'white' result from tests 20 and 21, the results show that the stack page takes priority.

For the people who got a 'black' result from tests 20 and 21, the results show that the zero page takes priority.

To find out why there is this different I have one last request.

If you can, please find out what revision of the 8722 you have in your c128, sadly there is no way to tell register-wise so you'll need to look at the chip markings, from what I can find it will be either 8722R1 or 8722R2.

I'm hoping the zp/sp priority difference is tied to the revision of the mmu.

Thanks in advance to the testers who are willing to go through the extra trouble.
2022-01-10 17:28

Registered: Feb 2006
Posts: 66
The NTSC 128D I've been providing results on is:
1788 22

(I'll open the flat if you really need but am not in a great rush to do so)
2022-01-10 17:56

Registered: Sep 2007
Posts: 41
thank you for the mmu rev jcompton.

I'll wait till more results come in before I ask anything else of you ;)
2022-01-10 19:14

Registered: Mar 2009
Posts: 3717
My tested PAL C128DCR (HB1 005865) has a MOS 8722R2 4786 22.

And I am sure we love to help. :) This is interesting and fun.
2022-01-10 19:48

Registered: Mar 2015
Posts: 30
4487 22
2022-01-10 20:06

Registered: Mar 2002
Posts: 50
Do you still take more results at a later time? I have three c128s here but cannot check right now.
2022-01-10 20:07

Registered: Dec 2001
Posts: 10257
The more data the better :)
2022-01-10 20:21

Registered: Nov 2006
Posts: 18
Results from my PAL C128 flat (HB51 42784)


00 green
01 green
02 green
03 green
04 black
05 green
06 blue
07 green
08 brown
09 green
10 green
11 green
12 green
13 green
14 blue
15 white
16 blue
17 cyan
18 white
19 green
20 white
21 white

...wondering if I even need to put back the top metal shield?
2022-01-13 03:14

Registered: Sep 2007
Posts: 41
Thank you all for the test results, we were able to learn a lot more from the results and have improved the emulation of x128 and Z64K.

The last part of this mmu testing adventure will be some z80 related tests, don't worry, you won't have to start cp/m or something, the test programs will switch to the z80, run the test and change the border color to indicate the result.

I will start making these tests on the weekend, since working life got in the way for now.
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