Out of the blue the other day, my friend found an internal 65C102 co-processor for the BBC Master in his attic, and gave it to me. It wasn't in particularly good physical condition (all the pins were bent) but I managed to get it connected, and it does appear to work! (Though I don't have any of the PCB stand-offs; I guess they're quite important to ensure the board isn't damaged by warping, so I should probably go and find some soon-ish).

However, I'm slightly more concerned than with most hardware, due to the condition that it was in, that there might be something wrong with it. While I can write a simple BASIC loop and see that it does indeed execute just over twice as fast as on the main processor, I'd like to test as much as the memory as is possible. I gather from the internet that the entire 64K address space of the thing is mapped to RAM, into which the chosen ROM is copied on boot? So I guess testing that bit won't be easy. Though I could easily write some BASIC to do some simple tests between PAGE and HIMEM (though that might be complicated since I suspect HIMEM especially will change during program execution!), and between &C000 and &F7FF (where "HI BASIC", which I also don't have a copy of, would usually sit), I wonder if there's a not-too-hard way to be a bit more thorough than this?

Unfortunately I've forgotten most things I used to know about my collection of 80s and early 90s home computers, since I had university between now and the last time I had access to them; so some basic things that I would have known how to do (eg getting files onto disk easily) are things that I can't do right now (especially since my main machine with a floppy controller is currently sitting dead). But I can remember the, err, basics of BASIC, and I can get files across using the tape interface.

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    I'm not familiar with the internal 65C102 on the Master. Is it connecting to the tube interface or piggy backing on the main processor? There are tube testers around for the Model B that may be of use. – Chenmunka Jan 7 '17 at 19:11
  • @Chenmunka It's really just an upgraded and internal version of the 6502 Second Processor, ie it uses the Tube. On the Master you can configure the Tube to use the internal or external interfaces. – Muzer Jan 7 '17 at 20:53
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    Afaik you could write a simple program to test all pages except itself, move itself elsewhere then test the page it previously occupied. (Write all 1s, read them, write all 0s, read them.) It would be relatively simple, so could be written using basic assembly. – wizzwizz4 Jan 8 '17 at 10:04
  • Here's a memory map (page 20). I recommend using &8000 to &AFFF to load the program initially, then moving the program to &4000 to &7FFF to test the &8000 to &AFFF block. – wizzwizz4 Jun 11 '17 at 18:17
  • The master has two tube interfaces, one external and one internal. – Peter Green Jun 20 '18 at 13:25

PAGE and HIMEM are what you might call "system variables" in BBC basics, they mark the bottom top of the memory available for Basic use, they are intiialised from OS-provided values but can be changed by the user.

On a regular BBC micro HIMEM will point to the bottom of screen memory, so it can change if you change screen modes (this BTW meant you couldn't change screen mode within a procedure, because the procedure stack grows down from HIMEM), but on a second processor it should always point to the bottom of the OS unless it is manually changed.

So what I would do if writing a ram tester is manually change HIMEM to give my program a small workspace, the program can then test the space between the new HIMEM and the old HIMEM without worrying about being stepped on by BASIC. If you are using regular Basic you can also test the area between BASIC and the OS.

For testing the area with BASIC in it you could just run a checksum and compare the results running it on the copy of BASIC in the second processor to the copy in the machine itself.

Not sure of any easy way to test the OS code area at the top and the workspace areas at the bottom.

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