collapseos/kernel/sdc.asm

382 lines
8.5 KiB
NASM
Raw Normal View History

; sdc
;
; Manages the initialization of a SD card and implement a block device to read
; and write from/to it, in SPI mode.
;
; Note that SPI can't really be used directly from the z80, so this part
; assumes that you have a device that handles SPI communication on behalf of
; the z80. This device is assumed to work in a particular way. See the
; "rc2014/sdcard" recipe for details.
;
; That device has 3 ports. One write-only port to make CS high, one to make CS
; low (data sent is irrelevant), and one read/write port to send and receive
; bytes with the card through the SPI protocol. The device acts as a SPI master
; and writing to that port initiates a byte exchange. Data from the slave is
; then placed on a buffer that can be read by reading the same port.
;
; It's through that kind of device that this code below is supposed to work.
; *** Defines ***
; SDC_PORT_CSHIGH: Port number to make CS high
; SDC_PORT_CSLOW: Port number to make CS low
; SDC_PORT_SPI: Port number to send/receive SPI data
; *** Consts ***
.equ SDC_BLKSIZE 512
; *** Variables ***
; 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_PTR+2
; Sector number currently in SDC_BUF. 0xff, it's initial value, means "no
; sector.
.equ SDC_BUFSEC SDC_BUF+SDC_BLKSIZE
; Whether the buffer has been written to. 0 means clean. 1 means dirty.
; (not used yet)
.equ SDC_BUFDIRTY SDC_BUFSEC+1
.equ SDC_RAMEND SDC_BUFDIRTY+1
; *** Code ***
; Wake the SD card up. After power up, a SD card has to receive at least 74
; dummy clocks with CS and DI high. We send 80.
sdcWakeUp:
out (SDC_PORT_CSHIGH), a
ld b, 10 ; 10 * 8 == 80
ld a, 0xff
.loop:
out (SDC_PORT_SPI), a
nop
djnz .loop
ret
; Initiate SPI exchange with the SD card. A is the data to send. Received data
; is placed in A.
sdcSendRecv:
out (SDC_PORT_SPI), a
nop
nop
in a, (SDC_PORT_SPI)
nop
nop
ret
; sdcSendRecv 0xff until the response is something else than 0xff for a maximum
; of 20 times. Returns 0xff if no response.
sdcWaitResp:
push bc
ld b, 20
.loop:
ld a, 0xff
call sdcSendRecv
inc a ; if 0xff, it's going to become zero
jr nz, .end ; not zero? good, that's our command
djnz .loop
.end:
; whether we had a success or failure, we return the result.
; But first, let's bring it back to its original value.
dec a
pop bc
ret
; Sends a command to the SD card, along with arguments and specified CRC fields.
; (CRC is only needed in initial commands though).
; A: Command to send
; H: Arg 1 (MSB)
; L: Arg 2
; D: Arg 3
; E: Arg 4 (LSB)
; C: CRC
;
; Returns R1 response in A.
;
; This does *not* handle CS. You have to select/deselect the card outside this
; routine.
sdcCmd:
; Wait until ready to receive commands
push af
call sdcWaitResp
pop af
call sdcSendRecv
; Arguments
ld a, h
call sdcSendRecv
ld a, l
call sdcSendRecv
ld a, d
call sdcSendRecv
ld a, e
call sdcSendRecv
; send CRC
ld a, c
call sdcSendRecv
; And now we just have to wait for a valid response...
jp sdcWaitResp ; return
; Send a command that expects a R1 response, handling CS.
sdcCmdR1:
out (SDC_PORT_CSLOW), a
call sdcCmd
out (SDC_PORT_CSHIGH), a
ret
; Send a command that expects a R7 response, handling CS. A R7 is a R1 followed
; by 4 bytes. Those 4 bytes are returned in HL/DE in the same order as in
; sdcCmd.
sdcCmdR7:
out (SDC_PORT_CSLOW), a
call sdcCmd
; We have our R1 response in A. Let's try reading the next 4 bytes in
; case we have a R3.
push af
ld a, 0xff
call sdcSendRecv
ld h, a
ld a, 0xff
call sdcSendRecv
ld l, a
ld a, 0xff
call sdcSendRecv
ld d, a
ld a, 0xff
call sdcSendRecv
ld e, a
pop af
out (SDC_PORT_CSHIGH), a
ret
; Initialize a SD card. This should be called at least 1ms after the powering
; up of the card. Sets result code in A. Zero means success, non-zero means
; error.
sdcInitialize:
push hl
push de
push bc
call sdcWakeUp
; Call CMD0 and expect a 0x01 response (card idle)
; This should be called multiple times. We're actually expected to.
; Let's call this for a maximum of 10 times.
ld b, 10
.loop1:
ld a, 0b01000000 ; CMD0
ld hl, 0
ld de, 0
ld c, 0x95
call sdcCmdR1
cp 0x01
jp z, .cmd0ok
djnz .loop1
; Nothing? error
jr .error
.cmd0ok:
; Then comes the CMD8. We send it with a 0x01aa argument and expect
; a 0x01aa argument back, along with a 0x01 R1 response.
ld a, 0b01001000 ; CMD8
ld hl, 0
ld de, 0x01aa
ld c, 0x87
call sdcCmdR7
cp 0x01
jr nz, .error
xor a
cp h ; H is zero
jr nz, .error
cp l ; L is zero
jr nz, .error
ld a, d
cp 0x01
jp nz, .error
ld a, e
cp 0xaa
jr nz, .error
; Now we need to repeatedly run CMD55+CMD41 (0x40000000) until we
; the card goes out of idle mode, that is, when it stops sending us
; 0x01 response and send us 0x00 instead. Any other response means that
; initialization failed.
.loop2:
ld a, 0b01110111 ; CMD55
ld hl, 0
ld de, 0
call sdcCmdR1
cp 0x01
jr nz, .error
ld a, 0b01101001 ; CMD41 (0x40000000)
ld hl, 0x4000
ld de, 0x0000
call sdcCmdR1
cp 0x01
jr z, .loop2
or a ; cp 0
jr nz, .error
; Success! out of idle mode!
; initialize variables
ld hl, 0
ld (SDC_PTR), hl
ld a, 0xff
ld (SDC_BUFSEC), a
xor a
ld (SDC_BUFDIRTY), a
jr .end
.error:
ld a, 0x01
.end:
pop bc
pop de
pop hl
ret
; Send a command to set block size to SDC_BLKSIZE to the SD card.
; Returns zero in A if a success, non-zero otherwise
sdcSetBlkSize:
push hl
push de
ld a, 0b01010000 ; CMD16
ld hl, 0
ld de, SDC_BLKSIZE
call sdcCmdR1
; Since we're out of idle mode, we expect a 0 response
; We need no further processing: A is already the correct value.
pop de
pop hl
ret
; Read block index specified in A and place the contents in (SDC_BUF).
; Doesn't check CRC. If the operation is a success, updates (SDC_BUFSEC) to the
; value of A.
; Returns 0 in A if success, non-zero if error.
sdcReadBlk:
push bc
push hl
out (SDC_PORT_CSLOW), a
ld hl, 0 ; read single block at addr A
ld d, 0
ld e, a ; E isn't touched in the rest of the routine
; and holds onto our original A
ld a, 0b01010001 ; CMD17
call sdcCmd
or a ; cp 0
jr nz, .error
; Command sent, no error, now let's wait for our data response.
ld b, 20
.loop1:
call sdcWaitResp
; 0xfe is the expected data token for CMD17
cp 0xfe
jr z, .loop1end
cp 0xff
jr nz, .error
djnz .loop1
jr .error ; timeout. error out
.loop1end:
; We received our data token!
; Data packets follow immediately, we have 512 of them to read
ld bc, SDC_BLKSIZE
ld hl, SDC_BUF
.loop2:
call sdcWaitResp
ld (hl), a
cpi ; a trick to inc HL and dec BC at the same time.
; P/V indicates whether BC reached 0
jp pe, .loop2 ; BC is not zero, loop
; Read our 2 CRC bytes
call sdcWaitResp
call sdcWaitResp
; success! Let's recall our orginal A arg and put it in SDC_BUFSEC
ld a, e
ld (SDC_BUFSEC), a
xor a
ld (SDC_BUFDIRTY), a
jr .end
.error:
; try to preserve error code
or a ; cp 0
jr nz, .end ; already non-zero
inc a ; zero, adjust
.end:
out (SDC_PORT_CSHIGH), a
pop hl
pop bc
ret
; *** shell cmds ***
sdcInitializeCmd:
.db "sdci", 0, 0, 0
call sdcInitialize
jp sdcSetBlkSize ; return
; *** 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.
; To do this, we compare the high 7 bits of (SDC_PTR) with (SDC_BUFSEC).
; If they're different, we need to load a new block.
push hl
ld a, (SDC_BUFSEC)
ld h, a
ld a, (SDC_PTR+1) ; high byte has bufsec in its high 7 bits
srl a
cp h
jr z, .noload
; not equal, we need to load a new sector. A already contains the
; sector to load.
call sdcReadBlk
jr nz, .error
.noload:
ld a, (SDC_PTR+1) ; high byte
and 0x01 ; is first bit set?
jr nz, .highbuf ; first bit set? we're in the "highbuf" zone.
; lowbuf zone
; Read byte from memory at proper offset in lowbuf (first 0x100 bytes)
ld hl, SDC_BUF
jr .read
.highbuf:
; Read byte from memory at proper offset in highbuf (0x100-0x1ff)
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
ld (SDC_PTR), hl
cp a ; ensure Z
jr .end
.error:
call unsetZ
.end:
pop hl
ret
sdcSeek:
ld (SDC_PTR), hl
ret
sdcTell:
ld hl, (SDC_PTR)
ret