NMI
FDC service deadline
NMI
0
5
10
15
µs
0
5
10
15
20
25
30
35
cyc.
NMI service timing for quad density floppy disc access
Greg Cook, 20/Sep/2010
Read from disc to I/O memory
Previous instruction
NMI sequence
LDA
fdc_data
EOR
#&FF
STA user,X
INX
BNE
exit
1MHzE
Read from disc to I/O memory at 2 MHz
.addr
.exit
Previous instruction
NMI sequence
LDA
fdc_data
EOR
#&FF
STA user,X
INX
BNE
exit
INC addr+2
Write from I/O memory to disc
.addr
Previous instruction
NMI sequence
EOR
#&FF
STA
fdc_data
INX
BNE
addr
INC addr+2
LDA user,X
1MHzE
Read from disc to coprocessor
Previous instruction
NMI sequence
LDA
fdc_data
EOR
#&FF
STA
tube_fifo_3
RTI
Write from coprocessor to disc
Previous instruction
NMI sequence
EOR
#&FF
STA
fdc_data
LDA
tube_fifo_3
RTI
Read sector IDs to coprocessor
.exit
Previous instruction
NMI sequence
LDA
fdc_data
EOR
#&FF
DEX
BMI
exit
STA
tube_fifo_3
RTI
Format disc from RLE table in I/O memory
.exit
Previous instruction
NMI sequence
STA
fdc_data
DEC counts,X
BNE
exit
INX
LDA bytes,X
Verify disc
Previous instruction
NMI sequence
BIT fdc_data
RTI
Read from disc to I/O memory, FDC on 1 MHz bus
Previous instruction
NMI sequence
LDA fdc_data
STA user,X
INX
BNE
exit
1MHzE
Read from disc to I/O memory at 2 MHz, FDC on 1 MHz bus
.addr
Previous instruction
NMI sequence
LDA fdc_data
STA user,X
INX
BNE
exit
INC addr+2
1MHzE
Write from I/O memory to disc, FDC on 1 MHz bus
.addr
Previous instruction
NMI sequence
STA fdc_data
INX
BNE
addr
INC addr+2
LDA user,X
1MHzE
Key:
= Fixed task
= FDC not serviced
= Service routine not re-entrant
= Working set on stack