mirror of
https://github.com/hsoft/collapseos.git
synced 2024-11-27 21:28:05 +11:00
292 lines
6.7 KiB
NASM
292 lines
6.7 KiB
NASM
; floppy
|
|
;
|
|
; Implement a block device around a TRS-80 floppy. It uses SVCs supplied by
|
|
; TRS-DOS to do so.
|
|
;
|
|
; *** Floppy buffers ***
|
|
;
|
|
; The dual-buffer system is exactly the same as in the "sdc" module. See
|
|
; comments there.
|
|
;
|
|
; *** Consts ***
|
|
; Number of sector per cylinder. We only support single density for now.
|
|
.equ FLOPPY_SEC_PER_CYL 10
|
|
.equ FLOPPY_MAX_CYL 40
|
|
.equ FLOPPY_BLKSIZE 256
|
|
|
|
; *** Variables ***
|
|
; This is a pointer to the currently selected buffer. This points to the BUFSEC
|
|
; part, that is, two bytes before actual content begins.
|
|
.equ FLOPPY_BUFPTR FLOPPY_RAMSTART
|
|
; Sector number currently in FLOPPY_BUF1. Little endian like any other z80 word.
|
|
.equ FLOPPY_BUFSEC1 @+2
|
|
; Whether the buffer has been written to. 0 means clean. 1 means dirty.
|
|
.equ FLOPPY_BUFDIRTY1 @+2
|
|
; The contents of the buffer.
|
|
.equ FLOPPY_BUF1 @+1
|
|
|
|
; second buffer has the same structure as the first.
|
|
.equ FLOPPY_BUFSEC2 @+FLOPPY_BLKSIZE
|
|
.equ FLOPPY_BUFDIRTY2 @+2
|
|
.equ FLOPPY_BUF2 @+1
|
|
.equ FLOPPY_RAMEND @+FLOPPY_BLKSIZE
|
|
|
|
; *** Code ***
|
|
floppyInit:
|
|
; Make sure that both buffers are flagged as invalid and not dirty
|
|
xor a
|
|
ld (FLOPPY_BUFDIRTY1), a
|
|
ld (FLOPPY_BUFDIRTY2), a
|
|
dec a
|
|
ld (FLOPPY_BUFSEC1), a
|
|
ld (FLOPPY_BUFSEC2), a
|
|
ret
|
|
|
|
; Returns whether D (cylinder) and E (sector) are in proper range.
|
|
; Z for success.
|
|
_floppyInRange:
|
|
ld a, e
|
|
cp FLOPPY_SEC_PER_CYL
|
|
jp nc, unsetZ
|
|
ld a, d
|
|
cp FLOPPY_MAX_CYL
|
|
jp nc, unsetZ
|
|
xor a ; set Z
|
|
ret
|
|
|
|
; Read sector index specified in E and cylinder specified in D and place the
|
|
; contents in buffer pointed to by (FLOPPY_BUFPTR).
|
|
; If the operation is a success, updates buffer's sector to the value of DE.
|
|
; Z on success
|
|
floppyRdSec:
|
|
call _floppyInRange
|
|
ret nz
|
|
|
|
push bc
|
|
push hl
|
|
|
|
ld a, 0x28 ; @DCSTAT
|
|
ld c, 1 ; hardcoded to drive :1 for now
|
|
rst 0x28
|
|
jr nz, .end
|
|
|
|
ld hl, (FLOPPY_BUFPTR) ; HL --> active buffer's sector
|
|
ld (hl), e ; sector
|
|
inc hl
|
|
ld (hl), d ; cylinder
|
|
inc hl ; dirty
|
|
inc hl ; data
|
|
ld a, 0x31 ; @RDSEC
|
|
rst 0x28 ; sets proper Z
|
|
.end:
|
|
pop hl
|
|
pop bc
|
|
ret
|
|
|
|
; Write the contents of buffer where (FLOPPY_BUFPTR) points to in sector
|
|
; associated to it. Unsets the the buffer's dirty flag on success.
|
|
; Z on success
|
|
floppyWrSec:
|
|
push ix
|
|
ld ix, (FLOPPY_BUFPTR) ; IX points to sector
|
|
xor a
|
|
cp (ix+2) ; dirty flag
|
|
pop ix
|
|
ret z ; don't write if dirty flag is zero
|
|
|
|
push hl
|
|
push de
|
|
push bc
|
|
ld hl, (FLOPPY_BUFPTR) ; sector
|
|
ld e, (hl)
|
|
inc hl ; cylinder
|
|
ld d, (hl)
|
|
call _floppyInRange
|
|
jr nz, .end
|
|
ld c, 1 ; drive
|
|
ld a, 0x28 ; @DCSTAT
|
|
rst 0x28
|
|
jr nz, .end
|
|
inc hl ; dirty
|
|
xor a
|
|
ld (hl), a ; undirty the buffer
|
|
inc hl ; data
|
|
ld a, 0x35 ; @WRSEC
|
|
rst 0x28 ; sets proper Z
|
|
.end:
|
|
pop bc
|
|
pop de
|
|
pop hl
|
|
ret
|
|
|
|
; Considering the first 15 bits of EHL, select the most appropriate of our two
|
|
; buffers and, if necessary, sync that buffer with the floppy. If the selected
|
|
; buffer doesn't have the same sector as what EHL asks, load that buffer from
|
|
; the floppy.
|
|
; If the dirty flag is set, we write the content of the in-memory buffer to the
|
|
; floppy before we read a new sector.
|
|
; Returns Z on success, NZ on error
|
|
floppySync:
|
|
push de
|
|
; Given a 24-bit address in EHL, extracts the 16-bit sector from it and
|
|
; place it in DE, following cylinder and sector rules.
|
|
; EH is our sector index, L is our offset within the sector.
|
|
|
|
ld d, e ; cylinder
|
|
ld a, h ; sector
|
|
; Let's process D first. Because our maximum number of sectors is 400
|
|
; (40 * 10), D can only be either 0 or 1. If it's 1, we set D to 25 and
|
|
; add 6 to A
|
|
inc d \ dec d
|
|
jr z, .loop1 ; skip
|
|
ld d, 25
|
|
add a, 6
|
|
.loop1:
|
|
cp FLOPPY_SEC_PER_CYL
|
|
jr c, .loop1end
|
|
sub FLOPPY_SEC_PER_CYL
|
|
inc d
|
|
jr .loop1
|
|
.loop1end:
|
|
ld e, a ; write final sector in E
|
|
; Let's first see if our first buffer has our sector
|
|
ld a, (FLOPPY_BUFSEC1) ; sector
|
|
cp e
|
|
jr nz, .notBuf1
|
|
ld a, (FLOPPY_BUFSEC1+1) ; cylinder
|
|
cp d
|
|
jr z, .buf1Ok
|
|
|
|
.notBuf1:
|
|
; Ok, let's check for buf2 then
|
|
ld a, (FLOPPY_BUFSEC2) ; sector
|
|
cp e
|
|
jr nz, .notBuf2
|
|
ld a, (FLOPPY_BUFSEC2+1) ; cylinder
|
|
cp d
|
|
jr z, .buf2Ok
|
|
|
|
.notBuf2:
|
|
; None of our two buffers have the sector we need, we'll need to load
|
|
; a new one.
|
|
|
|
; We select our buffer depending on which is dirty. If both are on the
|
|
; same status of dirtiness, we pick any (the first in our case). If one
|
|
; of them is dirty, we pick the clean one.
|
|
push de ; --> lvl 1
|
|
ld de, FLOPPY_BUFSEC1
|
|
ld a, (FLOPPY_BUFDIRTY1)
|
|
or a ; is buf1 dirty?
|
|
jr z, .ready ; no? good, that's our buffer
|
|
; yes? then buf2 is our buffer.
|
|
ld de, FLOPPY_BUFSEC2
|
|
|
|
.ready:
|
|
; At this point, DE points to one of our two buffers, the good one.
|
|
; Let's save it to FLOPPY_BUFPTR
|
|
ld (FLOPPY_BUFPTR), de
|
|
|
|
pop de ; <-- lvl 1
|
|
|
|
; We have to read a new sector, but first, let's write the current one
|
|
; if needed.
|
|
call floppyWrSec
|
|
jr nz, .end ; error
|
|
; Let's read our new sector in DE
|
|
call floppyRdSec
|
|
jr .end
|
|
|
|
.buf1Ok:
|
|
ld de, FLOPPY_BUFSEC1
|
|
ld (FLOPPY_BUFPTR), de
|
|
; Z already set
|
|
jr .end
|
|
|
|
.buf2Ok:
|
|
ld de, FLOPPY_BUFSEC2
|
|
ld (FLOPPY_BUFPTR), de
|
|
; Z already set
|
|
; to .end
|
|
.end:
|
|
pop de
|
|
ret
|
|
|
|
; Flush floppy buffers if dirty and then invalidates them.
|
|
; We invalidate them so that we allow the case where we swap disks after a
|
|
; flush. If we didn't invalidate the buffers, reading a swapped disk after a
|
|
; flush would yield data from the previous disk.
|
|
floppyFlush:
|
|
ld hl, FLOPPY_BUFSEC1
|
|
ld (FLOPPY_BUFPTR), hl
|
|
call floppyWrSec
|
|
ld hl, FLOPPY_BUFSEC2
|
|
ld (FLOPPY_BUFPTR), hl
|
|
call floppyWrSec
|
|
call floppyInit
|
|
xor a ; ensure Z
|
|
ret
|
|
|
|
; *** blkdev routines ***
|
|
|
|
; Make HL point to its proper place in FLOPPY_BUF.
|
|
; EHL currently is a 24-bit offset to read in the floppy. E=high byte,
|
|
; HL=low word. Load the proper sector in memory and make HL point to the
|
|
; correct data in the memory buffer.
|
|
_floppyPlaceBuf:
|
|
call floppySync
|
|
ret nz ; error
|
|
; At this point, we have the proper buffer in place and synced in
|
|
; (FLOPPY_BUFPTR). Only L is important
|
|
ld a, l
|
|
ld hl, (FLOPPY_BUFPTR)
|
|
inc hl ; sector MSB
|
|
inc hl ; dirty flag
|
|
inc hl ; contents
|
|
; DE is now placed on the data part of the active buffer and all we need
|
|
; is to increase DE by L.
|
|
call addHL
|
|
; Now, HL points exactly at the right byte in the active buffer.
|
|
xor a ; ensure Z
|
|
ret
|
|
|
|
floppyGetB:
|
|
push hl
|
|
call _floppyPlaceBuf
|
|
jr nz, .end ; NZ already set
|
|
|
|
; This is it!
|
|
ld a, (hl)
|
|
cp a ; ensure Z
|
|
.end:
|
|
pop hl
|
|
ret
|
|
|
|
floppyPutB:
|
|
push hl
|
|
push af ; --> lvl 1. let's remember the char we put,
|
|
; _floppyPlaceBuf destroys A.
|
|
call _floppyPlaceBuf
|
|
jr nz, .error
|
|
|
|
; HL points to our dest. Recall A and write
|
|
pop af ; <-- lvl 1
|
|
ld (hl), a
|
|
|
|
; Now, let's set the dirty flag
|
|
ld a, 1
|
|
ld hl, (FLOPPY_BUFPTR)
|
|
inc hl ; sector MSB
|
|
inc hl ; point to dirty flag
|
|
ld (hl), a ; set dirty flag
|
|
xor a ; ensure Z
|
|
jr .end
|
|
.error:
|
|
; preserve error code
|
|
ex af, af'
|
|
pop af ; <-- lvl 1
|
|
ex af, af'
|
|
call unsetZ
|
|
.end:
|
|
pop hl
|
|
ret
|