General Category > Lisa Troubleshooting and Repair
Lisa 2 started throwing Error 45
rayarachelian:
--- Quote from: dmark on May 08, 2022, 03:53:55 pm ---Sorry if this is an obvious question, but how do you test the CPU board in operation? Is there something like an extender board to run the computer with the card cage outside the case?
--- End quote ---
There's no such extender board, sorry. You might be able to create one, but the length of the wires would be an issue. You could desolder those 3 SRAMs and test them and then resolder them back with sockets?
stepleton:
Is it possible to get into Service Mode after an Error 45? If so, could you run some programs (or just do some memory reads and writes) to check whether the MMU registers are working as expected?
dmark:
--- Quote from: stepleton on May 08, 2022, 05:37:27 pm ---Is it possible to get into Service Mode after an Error 45? If so, could you run some programs (or just do some memory reads and writes) to check whether the MMU registers are working as expected?
--- End quote ---
Yes, it is indeed possible to enter Service Mode from Error 45, inspect memory and run programs, run diagnostic tests etc! (TIL)
I'm not familiar with how to test the MMU registers on a Lisa, however. Do you have any pointers where I can read up on this?
rayarachelian:
--- Quote from: dmark on May 08, 2022, 06:09:36 pm ---Yes, it is indeed possible to enter Service Mode from Error 45, inspect memory and run programs, run diagnostic tests etc! (TIL)
I'm not familiar with how to test the MMU registers on a Lisa, however. Do you have any pointers where I can read up on this?
--- End quote ---
I'd download a few versions of LisaTest and try those if you can boot at all. There's some way to go into the "Service Mode" advanced menu when it starts up and go into the individual tests.
Edit: looking at page 5.4 of http://bitsavers.org/pdf/apple/lisa/service/072-0085_Level_1_Lisa_Technical_Procedures_Mar85.pdf - it's the usual Apple-S to enter "Service Mode" in LisaTest as well as on the Boot ROM. D'oh! Surprised I forgot this factoid.
If you can't boot LisaTest, you could write some code to call the Boot ROM MMU routines, but that will be difficult to test unless you understand the Lisa's hardware and 68000 code. You'll need to write custom code, etc. As Tom mentions below there are a couple of routines to set/read the MMU registers.
There's also some code to do this in the ROM that you might be able to call - this might be harder if you do this with non "H" versions of the ROM as that's the only source we have for the Lisa Boot ROM, and earlier ones might not behave the same, etc.
But you'll have to play carefully with the MMU registers since any code you write will live in RAM and be invoked via service mode, and changing the MMU registers can cause that space (both the ROM routines and RAM you're writing code to) to disappear as it goes out of scope.
stepleton:
Oh neat. Well, this would be a Project, but hopefully an interesting one.
Your first port of call is probably the Lisa Hardware Manual and its description of how the MMU works (starting on PDF page 35).
Whatever code you make would have to ensure that the MMU is in the mode that allows you to write to the MMU registers. (This may already be the case in Service Mode --- I don't really remember.) Then you would write to the memory addresses where the MMU registers are and read them back to compare. Some care may be required since changing the MMU configuration may change whether you're still able to speak to the MMU in the first place.
Now for me there is nothing better than an example, and if you're similar, you'll want to check out the Lisa Boot ROM source code and see how it talks to the MMU.
You'd have to write your own code in assembly language, assemble it into hex data, and then type it into Service Mode and execute it and see what happens. You might use some of the utility routines in the Boot ROM to print out results (see the Boot ROM manual PDF page 20 and page 28 onward), or you can just stash results in RAM somewhere and then inspect those memory locations with the Service Mode memory inspection tool.
(@Ray, it looks like LisaTest won't boot based on earlier posts... maybe still worth a shot to see if getting into individual test mode still works? I don't remember how to do it either.)
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