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https://github.com/hsoft/collapseos.git
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367 lines
7.9 KiB
NASM
367 lines
7.9 KiB
NASM
; sdc
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;
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; Manages the initialization of a SD card and implement a block device to read
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; and write from/to it, in SPI mode.
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;
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; Note that SPI can't really be used directly from the z80, so this part
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; assumes that you have a device that handles SPI communication on behalf of
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; the z80. This device is assumed to work in a particular way.
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;
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; That device has 3 ports. One write-only port to make CS high, one to make CS
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; low (data sent is irrelevant), and one read/write port to send and receive
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; bytes with the card through the SPI protocol. The device acts as a SPI master
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; and writing to that port initiates a byte exchange. Data from the slave is
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; then placed on a buffer that can be read by reading the same port.
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;
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; It's through that kind of device that this code below is supposed to work.
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; *** Defines ***
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; SDC_PORT_CSHIGH: Port number to make CS high
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; SDC_PORT_CSLOW: Port number to make CS low
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; SDC_PORT_SPI: Port number to send/receive SPI data
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; *** Consts ***
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.equ SDC_BLKSIZE 512
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; *** Variables ***
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; Where the block dev current points to. This is a byte index. Higher 7 bits
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; indicate a sector number, lower 9 bits are an offset in the current SDC_BUF.
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.equ SDC_PTR SDC_RAMSTART
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; Whenever we read a sector, we read a whole block at once and we store it
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; in memory. That's where it goes.
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.equ SDC_BUF SDC_PTR+2
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.equ SDC_RAMEND SDC_BUF+SDC_BLKSIZE
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; *** Code ***
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; Wake the SD card up. After power up, a SD card has to receive at least 74
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; dummy clocks with CS and DI high. We send 80.
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sdcWakeUp:
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out (SDC_PORT_CSHIGH), a
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ld b, 10 ; 10 * 8 == 80
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ld a, 0xff
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.loop:
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out (SDC_PORT_SPI), a
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nop
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djnz .loop
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ret
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; Initiate SPI exchange with the SD card. A is the data to send. Received data
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; is placed in A.
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sdcSendRecv:
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out (SDC_PORT_SPI), a
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nop
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nop
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in a, (SDC_PORT_SPI)
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nop
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nop
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ret
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; sdcSendRecv 0xff until the response is something else than 0xff for a maximum
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; of 20 times. Returns 0xff if no response.
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sdcWaitResp:
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push bc
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ld b, 20
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.loop:
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ld a, 0xff
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call sdcSendRecv
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inc a ; if 0xff, it's going to become zero
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jr nz, .end ; not zero? good, that's our command
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djnz .loop
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.end:
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; whether we had a success or failure, we return the result.
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; But first, let's bring it back to its original value.
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dec a
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pop bc
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ret
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; Sends a command to the SD card, along with arguments and specified CRC fields.
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; (CRC is only needed in initial commands though).
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; A: Command to send
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; H: Arg 1 (MSB)
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; L: Arg 2
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; D: Arg 3
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; E: Arg 4 (LSB)
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; C: CRC
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;
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; Returns R1 response in A.
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;
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; This does *not* handle CS. You have to select/deselect the card outside this
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; routine.
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sdcCmd:
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; Wait until ready to receive commands
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push af
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call sdcWaitResp
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pop af
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call sdcSendRecv
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; Arguments
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ld a, h
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call sdcSendRecv
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ld a, l
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call sdcSendRecv
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ld a, d
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call sdcSendRecv
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ld a, e
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call sdcSendRecv
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; send CRC
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ld a, c
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call sdcSendRecv
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; And now we just have to wait for a valid response...
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call sdcWaitResp
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ret
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; Send a command that expects a R1 response, handling CS.
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sdcCmdR1:
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out (SDC_PORT_CSLOW), a
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call sdcCmd
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out (SDC_PORT_CSHIGH), a
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ret
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; Send a command that expects a R7 response, handling CS. A R7 is a R1 followed
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; by 4 bytes. Those 4 bytes are returned in HL/DE in the same order as in
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; sdcCmd.
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sdcCmdR7:
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out (SDC_PORT_CSLOW), a
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call sdcCmd
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; We have our R1 response in A. Let's try reading the next 4 bytes in
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; case we have a R3.
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push af
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ld a, 0xff
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call sdcSendRecv
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ld h, a
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ld a, 0xff
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call sdcSendRecv
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ld l, a
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ld a, 0xff
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call sdcSendRecv
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ld d, a
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ld a, 0xff
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call sdcSendRecv
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ld e, a
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pop af
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out (SDC_PORT_CSHIGH), a
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ret
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; Initialize a SD card. This should be called at least 1ms after the powering
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; up of the card. Sets result code in A. Zero means success, non-zero means
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; error.
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sdcInitialize:
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push hl
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push de
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push bc
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call sdcWakeUp
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; Call CMD0 and expect a 0x01 response (card idle)
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; This should be called multiple times. We're actually expected to.
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; Let's call this for a maximum of 10 times.
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ld b, 10
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.loop1:
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ld a, 0b01000000 ; CMD0
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ld hl, 0
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ld de, 0
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ld c, 0x95
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call sdcCmdR1
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cp 0x01
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jp z, .cmd0ok
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djnz .loop1
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; Nothing? error
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jr .error
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.cmd0ok:
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; Then comes the CMD8. We send it with a 0x01aa argument and expect
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; a 0x01aa argument back, along with a 0x01 R1 response.
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ld a, 0b01001000 ; CMD8
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ld hl, 0
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ld de, 0x01aa
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ld c, 0x87
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call sdcCmdR7
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cp 0x01
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jr nz, .error
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xor a
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cp h ; H is zero
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jr nz, .error
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cp l ; L is zero
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jr nz, .error
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ld a, d
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cp 0x01
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jp nz, .error
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ld a, e
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cp 0xaa
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jr nz, .error
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; Now we need to repeatedly run CMD55+CMD41 (0x40000000) until we
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; the card goes out of idle mode, that is, when it stops sending us
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; 0x01 response and send us 0x00 instead. Any other response means that
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; initialization failed.
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.loop2:
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ld a, 0b01110111 ; CMD55
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ld hl, 0
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ld de, 0
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call sdcCmdR1
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cp 0x01
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jr nz, .error
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ld a, 0b01101001 ; CMD41 (0x40000000)
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ld hl, 0x4000
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ld de, 0x0000
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call sdcCmdR1
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cp 0x01
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jr z, .loop2
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or a ; cp 0
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jr nz, .error
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; Success! out of idle mode!
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; We initialize out current PTR to 0
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ld hl, 0
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ld (SDC_PTR), hl
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jr .success
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.error:
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ld a, 0x01
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jr .end
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.success:
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xor a
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.end:
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pop bc
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pop de
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pop hl
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ret
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; Send a command to set block size to SDC_BLKSIZE to the SD card.
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; Returns zero in A if a success, non-zero otherwise
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sdcSetBlkSize:
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push hl
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push de
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ld a, 0b01010000 ; CMD16
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ld hl, 0
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ld de, SDC_BLKSIZE
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call sdcCmdR1
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; Since we're out of idle mode, we expect a 0 response
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; We need no further processing: A is already the correct value.
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pop de
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pop hl
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ret
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; Read block index specified in A and place the contents in (SDC_BUF).
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; Doesn't check CRC.
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; Returns 0 in A if success, non-zero if error.
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sdcReadBlk:
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push bc
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push hl
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out (SDC_PORT_CSLOW), a
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ld hl, 0 ; read single block at addr A
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ld d, 0
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ld e, a
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ld a, 0b01010001 ; CMD17
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call sdcCmd
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or a ; cp 0
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jr nz, .error
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; Command sent, no error, now let's wait for our data response.
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ld b, 20
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.loop1:
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call sdcWaitResp
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; 0xfe is the expected data token for CMD17
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cp 0xfe
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jr z, .loop1end
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cp 0xff
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jr nz, .error
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djnz .loop1
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jr .error ; timeout. error out
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.loop1end:
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; We received our data token!
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; Data packets follow immediately, we have 512 of them to read
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ld bc, SDC_BLKSIZE
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ld hl, SDC_BUF
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.loop2:
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call sdcWaitResp
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ld (hl), a
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cpi ; a trick to inc HL and dec BC at the same time.
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; P/V indicates whether BC reached 0
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jp pe, .loop2 ; BC is not zero, loop
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; Read our 2 CRC bytes
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call sdcWaitResp
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call sdcWaitResp
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; success!
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xor a
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jr .end
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.error:
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; try to preserve error code
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or a ; cp 0
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jr nz, .end ; already non-zero
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inc a ; zero, adjust
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.end:
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out (SDC_PORT_CSHIGH), a
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pop hl
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pop bc
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ret
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; *** shell cmds ***
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sdcInitializeCmd:
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.db "sdci", 0, 0, 0
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call sdcInitialize
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call sdcSetBlkSize
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ret
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; *** blkdev routines ***
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sdcGetC:
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; SDC_PTR points to the character we're supposed to read right now, but
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; we first have to check whether we need to load a new sector in memory.
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; This is rather easy: if the first 9 bits are zero, then we need to
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; read the sector in the high 7 bits.
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push hl
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xor a
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ld hl, (SDC_PTR)
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cp l ; is L zero?
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jr nz, .mem ; non-zero? no need to read a sector
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ld a, h
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and 0x1
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jr nz, .mem ; if H has first bit set, no need to read a
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; sector
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; Oh, first 9 bits unset. Se need to read a sector
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; H is already in A. We just need a right shift.
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rra ; now that's our sector
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call sdcReadBlk
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jr nz, .error
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.mem:
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; Read byte from memory at proper offset
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; Higher 256 bytes or lower ones?
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ld a, h
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and 0x1
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jr nz, .highbuf
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; We're on the lower part
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ld hl, SDC_BUF
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jr .read
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.highbuf:
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; We're on the higher part
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ld hl, SDC_BUF+0x100
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.read:
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; HL is now placed either on the lower or higher half of SDC_BUF and
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; all we need is to increase HL by the number in SDC_PTR's LSB (little
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; endian, remember).
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ld a, (SDC_PTR) ; LSB
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call addHL
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; This is it!
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ld a, (hl)
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; before we return A, we need to increase (SDC_PTR)
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ld hl, SDC_PTR
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inc (hl)
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cp a ; ensure Z
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jr .end
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.error:
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call unsetZ
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.end:
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pop hl
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ret
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