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;

; sctio-ser.s -- disk sector I/O for disk made available by serial interface

;

;***************************************************************

        .export sctcapser               ; determine disk capacity

        .export sctioser                ; do disk I/O

        .import ser1in

        .import ser1out

        .import ser1inchk

        .import puts

        ; constants for communication with disk server

        .set    SYN,0x16                ; to initiate the three-way handshake

        .set    ACK,0x06                ; acknowledgement for handshake

        .set    RESULT_OK,0x00          ; server successfully executed cmd

                                        ; everything else means error

        .set    WAIT_DELAY,800000       ; count for delay loop

;***************************************************************

        .code

        .align  4

sctcapser:

        sub     $29,$29,16

        stw     $16,$29,0

        stw     $17,$29,4

        stw     $18,$29,8

        stw     $31,$29,12

        add     $4,$0,trymsg             ; say what we are doing

        jal     puts

        add     $18,$0,$0         ; capacity == 0 if disk not present

        add     $16,$0,10                ; 10 tries to get a connection

handshake1:

        sub     $16,$16,1

        add     $4,$0,SYN

        jal     ser1out                 ; send SYN

        add     $17,$0,WAIT_DELAY        ; wait for ACK

handshake2:

        sub     $17,$17,1

        jal     ser1inchk

        bne     $2,$0,handshake3

        bne     $17,$0,handshake2

        add     $4,$0,timeoutmsg

        jal     puts

        bne     $16,$0,handshake1

        add     $4,$0,frustratedmsg

        jal     puts

        j       sctcapx

handshake3:

        jal     ser1in

        add     $8,$0,ACK

        bne     $2,$8,sctcapx

        ; we got an ACK so we return it

        add     $4,$0,ACK

        jal     ser1out

        ; ask it for its capacity

        add     $4,$0,'c'

        jal     ser1out                 ; request

        jal     ser1in                  ; first byte of response

        bne     $2,$0,sctcapx            ; exit if error

        ; all is well and the server will give us the capacity

        add     $16,$0,4         ; 4 bytes to read

sctcap1:

        sll     $18,$18,8

        jal     ser1in

        or      $18,$18,$2              ; most significant byte first

        sub     $16,$16,1

        bne     $16,$0,sctcap1

        ; return value is in $18

sctcapx:

        add     $2,$0,$18

        ldw     $16,$29,0

        ldw     $17,$29,4

        ldw     $18,$29,8

        ldw     $31,$29,12

        add     $29,$29,16

        jr      $31

        .data

        .align  4

trymsg:

        .byte   "Trying to connect to disk server..."

        .byte   0x0A, 0

timeoutmsg:

        .byte   "Request timed out..."

        .byte   0x0A, 0

frustratedmsg:

        .byte   "Unable to establish connection to disk server."

        .byte   0x0A, 0

        .code

        .align  4

sctioser:

        sub     $29,$29,24

        stw     $16,$29,0

        stw     $17,$29,4

        stw     $18,$29,8

        stw     $19,$29,12

        stw     $20,$29,16

        stw     $31,$29,20

        add     $16,$0,$4                ; command

        add     $17,$0,$5                ; start at sector

        add     $8,$0,0xc0000000

        or      $18,$8,$6               ; memory address (logicalized)

        add     $19,$0,$7                ; number of sectors

        ; switch over command

        add     $8,$0,'r'

        beq     $8,$16,sctior           ; read

        add     $8,$0,'w'

        beq     $8,$16,sctiow           ; write

        ; unknown command

        add     $2,$0,1                  ; value != 0 signifies error

        j       sctiox

        ; read from disk

sctior:

sctior1:                                ; loop over number of sectors

        beq     $19,$0,sctiorsuc ; successful return

        sub     $19,$19,1

        ; read a sector

        add     $4,$0,'r'

        jal     ser1out

        ; send sector number

        add     $20,$0,32                ; 4 bytes

sctior2:

        sub     $20,$20,8

        slr     $4,$17,$20

        and     $4,$4,0xff

        jal     ser1out

        bne     $20,$0,sctior2

        add     $17,$17,1

        ; get answer

        jal     ser1in

        bne     $2,$0,sctiox             ; $2 != 0 so we use it as return code

        ; read data

        add     $20,$0,512

sctior3:

        sub     $20,$20,1

        jal     ser1in

        stb     $2,$18,0

        add     $18,$18,1

        bne     $20,$0,sctior3

        j       sctior1

sctiorsuc:

        add     $2,$0,$0

        j       sctiox

        ; write to disk

sctiow:

sctiow1:                                ; loop over number of sectors

        beq     $19,$0,sctiowsuc ; successful return

        sub     $19,$19,1

        ; write a sector

        add     $4,$0,'w'

        jal     ser1out

        ; send sector number

        add     $20,$0,32                ; 4 bytes

sctiow2:

        sub     $20,$20,8

        slr     $4,$17,$20

        and     $4,$4,0xff

        jal     ser1out

        bne     $20,$0,sctiow2

        add     $17,$17,1

        ; write data

        add     $20,$0,512

sctiow3:

        sub     $20,$20,1

        ldbu    $4,$18,0

        jal     ser1out

        add     $18,$18,1

        bne     $20,$0,sctiow3

        ; get answer

        jal     ser1in

        bne     $2,$0,sctiox

        j       sctiow1

sctiowsuc:

        add     $2,$0,$0

sctiox:

        ldw     $16,$29,0

        ldw     $17,$29,4

        ldw     $18,$29,8

        ldw     $19,$29,12

        ldw     $20,$29,16

        ldw     $31,$29,20

        add     $29,$29,24

        jr      $31