I'm using an essentially unmodified version of the PIC firmware that I developed for the Atom interface. It's written in C and is structured in such a way that the business end of things can be lifted out and driven by an emulator instead of actual interface hardware. This is invaluable for debugging client code - especially when a stupid error might mean a 2 minute delay while a tape loads...
Anyway, they say a picture speaks a thousand words so here's my 1K ...
- 0000.png (1.86 KiB) Viewed 39681 times
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; init directory reader
;
ld b,2 ; directory control
ld l,0 ; 0 = reset directory reader
ld c,7
out (c),l
call response
call expect_3f ; error if != $3f
getdirent:
ld b,2 ; directory control
ld l,1 ; 1 = get next directory entry
ld c,7
out (c),l
call response
cp $3f
jr z,gotentry ; $3f = continue
cp $40
jr z,alldone ; $40 = finished
call expect_3f ; error if != $3f
alldone:
ret
gotentry:
ld b,6 ; acquire data control
ld l,$3f ; 3f = reset data reader
ld c,7
out (c),l
jr readentry
printchar:
rst 10h
readentry:
in a,(c) ; collect a character from the filename
jr nz,printchar
ld a,$76 ; print a newline
rst 10h
jr getdirent
response:
; mustn't change BC contents
ld l,0 ; delay loop setting
rsp_delay:
dec l
jr nz,rsp_delay
in a,(c) ; get response code
jp m,rsp_delay ; and loop whilst negative
ret
expect_3f
cp $3f
jr nz,exp_itsbad
ret
exp_itsbad:
sub $41-10
rst 08h
- ratty.jpg (230.61 KiB) Viewed 39683 times
But the wait was unavoidable. And it has meant that the development of this board will be much quicker 
