Sam

Quick update: Acorn DFS 2.26 performs multiple sector writes one at a time rather than all in one go, whereas DDOS writes them all in one operation.

When I take NMILock out of the equation during the 1770 poll function, the issue disappears on DDOS 3.45 (and a test program I wrote based on the datasheet). DDOS...

@chrisn does a list of DFS* and a test Beeb program exist that the 1770 emulation has previously been tested with? I'm fine writing the program to give the FDC...

Hmmm. I saw the last change to that line was a very long time ago and felt sure I'd seen DDOS working since then. It would seem not. It does...

Actually, before I do that, NMILock appears to be related to the 6502 not attempting to re-enter the NMI routine whilst an existing one is running (haven't got the datasheet...

A further thought on that is that a WD1770PH 02-02 variant could be clocked at 16MHz to allow it to read/write HD floppy disks, although it was _incredibly_ tight fitting...

I still think I need to write a program to test Read Address, though. I haven't explicitly tried that, although I can't think of a reason it would be any...

Timing diagram confirms that - a NMI can interrupt a NMI. Didn't know that - I guess there's usually only one NMI source in a lot of cases so unlikely...

You said 1.54T worked with the Watford board selected before. Sure you had the right board selected during that last test? General behaviour I've seen with non-Acorn DFS's is to...

Ok. I'll have a look at what it's trying to do, NMI code first. Assuming Shift+Break did the same? That FS is DD only, isn't it?