17-07-2025, 05:36 PM
Another quick update.
As part of the OS development work, I've now implemented system support to be able to access the files on the SDcard (in the FAT FS) so that you can directly read or write
the files from CP/M rather than just the files available through the Microbee Disk images. The method is practically the same as calling CP/M's BDOS routines - in fact they have all
the same Call Numbers eg: Open File = 15, Close File = 16, Read Sequential = 20, Write Sequential = 21, Set DMA address = 26.
It involves writing to 3 I/O ports : one for the Call Number, one for High DMA / FCB address, one for Low DMA / FCB address. Write the address bytes first (if required) then the write
to the Call number triggers the M68K processor to handle the request and DMA the result back to Z80 memory space (for example).
More on this later.
Off to Canberra tomorrow for the Canberra Vintage Computer Exhibition.
As part of the OS development work, I've now implemented system support to be able to access the files on the SDcard (in the FAT FS) so that you can directly read or write
the files from CP/M rather than just the files available through the Microbee Disk images. The method is practically the same as calling CP/M's BDOS routines - in fact they have all
the same Call Numbers eg: Open File = 15, Close File = 16, Read Sequential = 20, Write Sequential = 21, Set DMA address = 26.
It involves writing to 3 I/O ports : one for the Call Number, one for High DMA / FCB address, one for Low DMA / FCB address. Write the address bytes first (if required) then the write
to the Call number triggers the M68K processor to handle the request and DMA the result back to Z80 memory space (for example).
Off to Canberra tomorrow for the Canberra Vintage Computer Exhibition.