collapseos/kernel/core.asm
Virgil Dupras ae028e3a86 blockdev: make implementors "random access"
This huge refactoring remove the Seek and Tell routine from blockdev
implementation requirements and change GetC and PutC's API so that they
take an address to read and write (through HL/DE) at each call.

The "PTR" approach in blockdev implementation was very redundant from
device to device and it made more sense to generalize. It's possible
that future device aren't "random access", but we'll be able to add more
device types later.

Another important change in this commit is that the "blockdev handle" is
now opaque. Previously, consumers of the API would happily call routines
directly from one of the 4 offsets. We can't do that any more. This
makes the API more solid for future improvements.

This change forced me to change a lot of things in fs, but overall,
things are now simpler. No more `FS_PTR`: the "device handle" now holds
the active pointer.

Lots, lots of changes, but it also feels a lot cleaner and solid.
2019-06-04 15:36:20 -04:00

252 lines
4.3 KiB
NASM

; core
;
; Routines used by pretty much all parts. You will want to include it first
; in your glue file.
; *** CONSTS ***
.equ ASCII_CR 0x0d
.equ ASCII_LF 0x0a
; *** DATA ***
; Useful data to point to, when a pointer is needed.
P_NULL: .db 0
; *** REGISTER FIDDLING ***
; add the value of A into DE
addDE:
push af
add a, e
jr nc, .end ; no carry? skip inc
inc d
.end:
ld e, a
pop af
noop: ; piggy backing on the first "ret" we have
ret
; copy (DE) into DE, little endian style (addresses in z80 are always have
; their LSB before their MSB)
intoDE:
push af
ld a, (de)
inc de
ex af, af'
ld a, (de)
ld d, a
ex af, af'
ld e, a
pop af
ret
intoHL:
push de
ex de, hl
call intoDE
ex de, hl
pop de
ret
intoIX:
push de
push ix \ pop de
call intoDE
push de \ pop ix
pop de
ret
; add the value of A into HL
addHL:
push af
add a, l
jr nc, .end ; no carry? skip inc
inc h
.end:
ld l, a
pop af
ret
; subtract the value of A from HL
subHL:
push af
; To avoid having to swap L and A, we sub "backwards", that is, we add
; a NEGated value. This means that the carry flag is inverted
neg
add a, l
jr c, .end ; if carry, no carry. :)
dec h
.end:
ld l, a
pop af
ret
; Compare HL with DE and sets Z and C in the same way as a regular cp X where
; HL is A and DE is X.
cpHLDE:
ld a, h
cp d
ret nz ; if not equal, flags are correct
ld a, l
cp e
ret ; flags are correct
; Write the contents of HL in (DE)
writeHLinDE:
push af
ld a, l
ld (de), a
inc de
ld a, h
ld (de), a
dec de
pop af
ret
; Call the method (IX) is a pointer to. In other words, call intoIX before
; callIX
callIXI:
push ix
call intoIX
call callIX
pop ix
ret
; jump to the location pointed to by IX. This allows us to call IX instead of
; just jumping it. We use IX because we seldom use this for arguments.
callIX:
jp (ix)
callIY:
jp (iy)
; Ensures that Z is unset (more complicated than it sounds...)
unsetZ:
push bc
ld b, a
inc b
cp b
pop bc
ret
; *** STRINGS ***
; Fill B bytes at (HL) with A
fill:
push bc
push hl
.loop:
ld (hl), a
inc hl
djnz .loop
pop hl
pop bc
ret
; Increase HL until the memory address it points to is equal to A for a maximum
; of 0xff bytes. Returns the new HL value as well as the number of bytes
; iterated in A.
; If a null char is encountered before we find A, processing is stopped in the
; same way as if we found our char (so, we look for A *or* 0)
; Set Z if the character is found. Unsets it if not
findchar:
push bc
ld c, a ; let's use C as our cp target
ld a, 0xff
ld b, a
.loop: ld a, (hl)
cp c
jr z, .match
or a ; cp 0
jr z, .nomatch
inc hl
djnz .loop
.nomatch:
call unsetZ
jr .end
.match:
; We ran 0xff-B loops. That's the result that goes in A.
ld a, 0xff
sub b
cp a ; ensure Z
.end:
pop bc
ret
; Format the lower nibble of A into a hex char and stores the result in A.
fmtHex:
and 0xf
cp 10
jr nc, .alpha ; if >= 10, we have alpha
add a, '0'
ret
.alpha:
add a, 'A'-10
ret
; Formats value in A into a string hex pair. Stores it in the memory location
; that HL points to. Does *not* add a null char at the end.
fmtHexPair:
push af
; let's start with the rightmost char
inc hl
call fmtHex
ld (hl), a
; and now with the leftmost
dec hl
pop af
push af
and 0xf0
rra \ rra \ rra \ rra
call fmtHex
ld (hl), a
pop af
ret
; Compares strings pointed to by HL and DE up to A count of characters. If
; equal, Z is set. If not equal, Z is reset.
strncmp:
push bc
push hl
push de
ld b, a
.loop:
ld a, (de)
cp (hl)
jr nz, .end ; not equal? break early. NZ is carried out
; to the called
cp 0 ; If our chars are null, stop the cmp
jr z, .end ; The positive result will be carried to the
; caller
inc hl
inc de
djnz .loop
; We went through all chars with success, but our current Z flag is
; unset because of the cp 0. Let's do a dummy CP to set the Z flag.
cp a
.end:
pop de
pop hl
pop bc
; Because we don't call anything else than CP that modify the Z flag,
; our Z value will be that of the last cp (reset if we broke the loop
; early, set otherwise)
ret
; Transforms the character in A, if it's in the a-z range, into its upcase
; version.
upcase:
cp 'a'
ret c ; A < 'a'. nothing to do
cp 'z'+1
ret nc ; A >= 'z'+1. nothing to do
; 'a' - 'A' == 0x20
sub 0x20
ret