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parts/z80/sdc: implement blockdev's GetC

This commit is contained in:
Virgil Dupras 2019-05-09 10:47:57 -04:00
parent 65a666bfda
commit d8bc9c2bdd
2 changed files with 80 additions and 9 deletions

View File

@ -24,11 +24,12 @@
.equ SDC_BLKSIZE 512
; *** Variables ***
; Index of the sector currently contained in SDC_BUF
.equ SDC_SECTOR SDC_RAMSTART
; Where the block dev current points to. This is a byte index. Higher 7 bits
; indicate a sector number, lower 9 bits are an offset in the current SDC_BUF.
.equ SDC_PTR SDC_RAMSTART
; Whenever we read a sector, we read a whole block at once and we store it
; in memory. That's where it goes.
.equ SDC_BUF SDC_SECTOR+1
.equ SDC_BUF SDC_PTR+2
.equ SDC_RAMEND SDC_BUF+SDC_BLKSIZE
; *** Code ***
@ -211,6 +212,9 @@ sdcInitialize:
or a ; cp 0
jr nz, .error
; Success! out of idle mode!
; We initialize out current PTR to 0
ld hl, 0
ld (SDC_PTR), hl
jr .success
.error:
@ -244,9 +248,9 @@ sdcSetBlkSize:
; Read block index specified in A and place the contents in (SDC_BUF).
; Doesn't check CRC.
; Returns 0 in A if success, non-zero if error.
; Returns SDC_BUF in HL
sdcReadBlk:
push bc
push hl
out (SDC_PORT_CSLOW), a
ld hl, 0 ; read single block at addr A
@ -292,6 +296,71 @@ sdcReadBlk:
inc a ; zero, adjust
.end:
out (SDC_PORT_CSHIGH), a
ld hl, SDC_BUF
pop hl
pop bc
ret
; *** shell cmds ***
sdcInitializeCmd:
.db "sdci", 0, 0, 0
call sdcInitialize
call sdcSetBlkSize
ret
; *** blkdev routines ***
sdcGetC:
; SDC_PTR points to the character we're supposed to read right now, but
; we first have to check whether we need to load a new sector in memory.
; This is rather easy: if the first 9 bits are zero, then we need to
; read the sector in the high 7 bits.
push hl
xor a
ld hl, (SDC_PTR)
cp l ; is L zero?
jr nz, .mem ; non-zero? no need to read a sector
ld a, h
and 0x1
jr nz, .mem ; if H has first bit set, no need to read a
; sector
; Oh, first 9 bits unset. Se need to read a sector
; H is already in A. We just need a right shift.
rra ; now that's our sector
call sdcReadBlk
jr nz, .error
.mem:
; Read byte from memory at proper offset
; Higher 256 bytes or lower ones?
ld a, h
and 0x1
jr nz, .highbuf
; We're on the lower part
ld hl, SDC_BUF
jr .read
.highbuf:
; We're on the higher part
ld hl, SDC_BUF+0x100
.read:
; HL is now placed either on the lower or higher half of SDC_BUF and
; all we need is to increase HL by the number in SDC_PTR's LSB (little
; endian, remember).
ld a, (SDC_PTR) ; LSB
call addHL
; This is it!
ld a, (hl)
; before we return A, we need to increase (SDC_PTR)
ld hl, SDC_PTR
inc (hl)
cp a ; ensure Z
jr .end
.error:
call unsetZ
.end:
pop hl
ret

View File

@ -35,8 +35,6 @@ init:
call blkSel
call shellInit
; TODO - block device creation
ei
jp shellLoop
@ -48,16 +46,20 @@ ACIA_RAMSTART .equ RAMSTART
STDIO_RAMSTART .equ ACIA_RAMEND
#include "stdio.asm"
BLOCKDEV_RAMSTART .equ STDIO_RAMEND
BLOCKDEV_COUNT .equ 1
BLOCKDEV_COUNT .equ 2
#include "blockdev.asm"
; List of devices
.dw aciaGetC, aciaPutC, 0, 0
.dw sdcGetC, 0, 0, 0
#include "blockdev_cmds.asm"
SHELL_RAMSTART .equ BLOCKDEV_RAMEND
.define SHELL_IO_GETC call blkGetCW
.define SHELL_IO_PUTC call blkPutC
SHELL_EXTRA_CMD_COUNT .equ 0
SHELL_EXTRA_CMD_COUNT .equ 3
#include "shell.asm"
.dw sdcInitializeCmd, blkBselCmd, blkSeekCmd
.equ SDC_RAMSTART SHELL_RAMEND
.equ SDC_PORT_CSHIGH 6