Compact flash on the Amstrad NC200

[hjalfi]

Oh, yeah, I forgot that (it's not actually in the 'documentation', and that bit is marked as reserved). However the motor doesn't actually come on when the program runs and it's cached.

sfx: looks at code

Aha, there's a sort of bug where every clock tick the interrupt handler turns the motor off again. Maybe that's worth fixing. The core problem is that port's not readable so I can't change it without reading the shadow copy, which (a) that standalone program can't access and (b) I don't actually keep a shadow copy yet anyway...

[dreNorteR]

Oh, yeah, I forgot that (it's not actually in the 'documentation', and that bit is marked as reserved). However the motor doesn't actually come on when the program runs and it's cached.

sfx: looks at code

Aha, there's a sort of bug where every clock tick the interrupt handler turns the motor off again. Maybe that's worth fixing. The core problem is that port's not readable so I can't change it without reading the shadow copy, which (a) that standalone program can't access and (b) I don't actually keep a shadow copy yet anyway...

So I imagine what was happening is that every register access turned the motor on again, then the timer fires and turns it off. 100 Hz buzzer
Maybe put the copy of the port at some fixed address in your BIOS?

[hjalfi]

It lives! Aha! Aaahaaa!

That deblocking code was *horrible*, and I spent ages tracing down heisenbugs which I *think* were due to a bad filesystem... I reran my mkfs tool, after fixing the bugs, and it worked fine. But creating a CP/M file system is so simple that I'm not sure how? Anyway, it's here: https://github.com/davidgiven/cpmish...sor/pcmcia.inc

It'll detect an ATA PCMCIA card on startup, set up the DPB accordingly, and then you can use it as a fixed disk. You can have up to a 32MB file system (I have 5 spare bytes of BIOS memory before I have to claim another page of TPA). Performance is great. With my old Lexar 16MB card the screen flakes out a bit during writes, which is a little scary.

Fun tip: I made the CP/M track/sector to LBA maths much easier by using 1024 CP/M sectors per track. This means that the CP/M track number drops into the middle two bytes of the LBA, so the only maths required is to shift the sector number right by two to get the low byte. Of such things Z80 code is made.

[tingo]

Nice!