source: xtideuniversalbios/trunk/Assembly_Library/Src/Serial/SerialServer.asm @ 277

; Project name  :   Assembly Library
; Description   :   Serial Server Support

%include "SerialServer.inc"
        
; Section containing code
SECTION .text

;--------------------------------------------------------------------
; SerialServer_SendReceive:     
;   Parameters:
;       DX:     Packed I/O port and baud rate
;       ES:SI:  Ptr to buffer (for data transfer commands)
;       SS:BP:  Ptr to SerialServer_Command structure
;   Returns:
;       AH:     INT 13h Error Code
;       CX:     Number of 512-byte blocks transferred
;       CF:     Cleared if success, Set if error
;   Corrupts registers:
;       AL, BX, CX, DX
;--------------------------------------------------------------------
SerialServer_SendReceive:       
        
        push    si
        push    di
        push    bp

;
; Unpack I/O port and baud from DPT
;       Port to DX for the remainder of the routine (+/- different register offsets)
;       Baud in CH until UART initialization is complete
;
        mov     ch,dh
        xor     dh,dh
        eSHL_IM dx, 2           ; shift from one byte to two

        mov     al,[bp+SerialServer_Command.bSectorCount]
        mov     ah,[bp+SerialServer_Command.bCommand]
;
; Command byte and sector count live at the top of the stack, pop/push are used to access
;
        push    ax              ; save sector count for return value
        push    ax              ; working copy on the top of the stack

        cld

;----------------------------------------------------------------------
;
; Initialize UART
;
; We do this each time since DOS (at boot) or another program may have
; decided to reprogram the UART
;
        mov     bl,dl           ; setup BL with proper values for read/write loops (BH comes later)

        mov     al,83h
        add     dl,Serial_UART_lineControl
        out     dx,al

        mov     al,ch
        mov     dl,bl           ; divisor low
        out     dx,al

        xor     ax,ax
        inc     dx              ; divisor high
        push    dx
        out     dx,al

        mov     al,047h
        inc     dx              ;  fifo
        out     dx,al

        mov     al,03h
        inc     dx              ;  linecontrol
        out     dx,al

        mov     al,0bh
        inc     dx              ;  modemcontrol
        out     dx,al

        inc     dx              ;  linestatus (no output now, just setting up BH for later use)
        mov     bh,dl

        pop     dx              ; base, interrupts disabled
        xor     ax,ax
        out     dx,al

;----------------------------------------------------------------------
;
; Send Command
;
; Sends first six bytes of IDEREGS_AND_INTPACK as the command
;
        push    es              ; save off real buffer location
        push    si

        mov     si,bp           ; point to IDEREGS for command dispatch;
        push    ss
        pop     es

        mov     di,0ffffh       ; initialize checksum for write
        mov     bp,di

        mov     cx,4            ; writing 3 words (plus 1)

        cli                     ; interrupts off...

        call    SerialServer_WriteProtocol.entry

        pop     di              ; restore real buffer location (note change from SI to DI)
                                ; Buffer is primarily referenced through ES:DI throughout, since
                                ; we need to store (read sector) faster than we read (write sector)
        pop     es

        pop     ax              ; load command byte (done before call to .nextSector on subsequent iterations)
        push    ax

        test    al,al           ; if no sectors to be transferred, wait for the ACK checksum on the command
        jz      .zeroSectors

;
; Top of the read/write loop, one iteration per sector
;
.nextSector:
        mov     si,0ffffh       ; initialize checksum for read or write
        mov     bp,si

        mov     cx,0101h        ; writing 256 words (plus 1)

        shr     ah,1            ; command byte, are we doing a write?
        jnc     .readEntry

        xchg    si,di           ; swap pointer and checksum, will be re-swap'ed in WriteProtocol
        call    SerialServer_WriteProtocol.entry

.zeroSectors:
        inc     cx              ; CX = 1 now (0 out of WriteProtocol)
        jmp     .readEntry

;----------------------------------------------------------------------
;
; Timeout
;
; To save code space, we use the contents of DL to decide which byte in the word to return for reading.
;
.readTimeout:
        push    ax              ; not only does this push preserve AX (which we need), but it also
                                ; means the stack has the same number of bytes on it as when we are
                                ; sending a packet, important for error cleanup and exit
        mov     ah,1
        call    SerialServer_WaitAndPoll_Read
        pop     ax
        test    dl,1
        jz      .readByte1Ready
        jmp     .readByte2Ready

;----------------------------------------------------------------------------
;
; Read Block (without interrupts, used when there is a FIFO, high speed)
;
; NOTE: This loop is very time sensitive.  Literally, another instruction
; cannot be inserted into this loop without us falling behind at high
; speed (460.8K baud) on a 4.77Mhz 8088, making it hard to receive
; a full 512 byte block.
;
.readLoop:
        stosw                   ; store word in caller's data buffer

        add     bp, ax          ; update Fletcher's checksum
        adc     bp, 0
        add     si, bp
        adc     si, 0

.readEntry:
        mov     dl,bh
        in      al,dx
        shr     al,1            ; data ready (byte 1)?
        mov     dl,bl           ; get ready to read data
        jnc     .readTimeout    ; nope not ready, update timeouts

;
; Entry point after initial timeout.  We enter here so that the checksum word
; is not stored (and is left in AX after the loop is complete).
;
.readByte1Ready:
        in      al, dx          ; read data byte 1

        mov     ah, al          ; store byte in ah for now

;
; note the placement of this reset of dl to bh, and that it is
; before the return, which is assymetric with where this is done
; above for byte 1.  The value of dl is used by the timeout routine
; to know which byte to return to (.read_byte1_ready or
; .read_byte2_ready)
;
        mov     dl,bh

        in      al,dx
        shr     al,1            ; data ready (byte 2)?
        jnc     .readTimeout
.readByte2Ready:
        mov     dl,bl
        in      al, dx          ; read data byte 2

        xchg    al, ah          ; ah was holding byte 1, reverse byte order

        loop    .readLoop

        sti                     ; interrupts back on ASAP, between packets

;
; Compare checksums
;
        xchg    ax,bp
        xor     ah,al
        mov     cx,si
        xor     cl,ch
        mov     al,cl
        cmp     ax,bp
        jnz     SerialServer_OutputWithParameters_Error

        pop     ax              ; sector count and command byte
        dec     al              ; decrement sector count
        push    ax              ; save
        jz      SerialServer_OutputWithParameters_ReturnCodeInAL

        cli                     ; interrupts back off for ACK byte to host
                                ; (host could start sending data immediately)
        out     dx,al           ; ACK with next sector number

        jmp     short .nextSector

;---------------------------------------------------------------------------
;
; Cleanup, error reporting, and exit
;

;
; Used in situations where a call is underway, such as with SerialServer_WaitAndPoll
;
ALIGN JUMP_ALIGN
SerialServer_OutputWithParameters_ErrorAndPop4Words:
        add     sp,8
;;; fall-through

ALIGN JUMP_ALIGN
SerialServer_OutputWithParameters_Error:
;----------------------------------------------------------------------
;
; Clear read buffer
;
; In case there are extra characters or an error in the FIFO, clear it out.
; In theory the initialization of the UART registers above should have
; taken care of this, but I have seen cases where this is not true.
;
        xor     cx,cx                   ; timeout this clearing routine, in case the UART isn't there
.clearBuffer:
        mov     dl,bh
        in      al,dx
        mov     dl,bl
        test    al,08fh
        jz      .clearBufferComplete
        test    al,1
        in      al,dx
        loopnz  .clearBuffer            ; note ZF from test above

.clearBufferComplete:
        mov     al, 3           ;  error return code and CF (low order bit)

ALIGN JUMP_ALIGN
SerialServer_OutputWithParameters_ReturnCodeInAL:
%if 0
        sti                     ;  all paths here will already have interrupts turned back on
%endif
        mov     ah, al          ;  for success, AL will already be zero
        
        pop     bx              ;  recover "ax" (command and count) from stack
        pop     cx              ;  recover saved sector count
        mov     ch, 0
        sub     cl, bl          ; subtract off the number of sectors that remained

        pop     bp
        pop     di
        pop     si

        shr     ah, 1           ; shift down return code and CF

        ret

;--------------------------------------------------------------------
; SerialServer_WriteProtocol
;
; NOTE: As with its read counterpart, this loop is very time sensitive.
; Although it will still function, adding additional instructions will
; impact the write throughput, especially on slower machines.
;
;   Parameters:
;       ES:SI:  Ptr to buffer
;       CX:     Words to write, plus 1
;       BP/DI:  Initialized for Checksum (-1 in each)
;       DH:     I/O Port high byte
;       BX:     LineStatus Register address (BH) and Receive/Transmit Register address (BL)
;   Returns:
;       BP/SI:  Checksum for written bytes, compared against ACK from server in .readLoop
;       CX:     Zero
;       DL:     Receive/Transmit Register address
;       ES:DI:  Ptr to buffer
;   Corrupts registers:
;       AX
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
SerialServer_WriteProtocol:
.writeLoop:
        es lodsw                ; fetch next word

        out     dx,al           ; output first byte

        add     bp,ax           ; update checksum
        adc     bp,0
        add     di,bp
        adc     di,0

        mov     dl,bh           ; transmit buffer empty?
        in      al,dx
        test    al,20h
        jz      .writeTimeout2  ; nope, use our polling routine

.writeByte2Ready:
        mov     dl,bl
        mov     al,ah           ; output second byte
        out     dx,al

.entry:
        mov     dl,bh           ; transmit buffer empty?
        in      al,dx
        test    al,20h
        mov     dl,bl
        jz      .writeTimeout1  ; nope, use our polling routine

.writeByte1Ready:
        loop    .writeLoop

        mov     ax,di           ; fold Fletcher's checksum and output
        xor     al,ah
        out     dx,al           ; byte 1

        call    SerialServer_WaitAndPoll_Write

        mov     ax,bp
        xor     al,ah
        out     dx,al           ; byte 2

        xchg    si,di           ; preserve checksum word in si, move pointer back to di

        ret

.writeTimeout2:
        mov     dl,ah           ; need to preserve AH, but don't need DL (will be reset upon return)
        call    SerialServer_WaitAndPoll_Write
        mov     ah,dl
        jmp     .writeByte2Ready

.writeTimeout1:
%ifndef USE_186
        mov     ax,.writeByte1Ready
        push    ax              ; return address for ret at end of SC_writeTimeout2
%else
        push    .writeByte1Ready
%endif
;;; fall-through

;--------------------------------------------------------------------
; SerialServer_WaitAndPoll
;
;   Parameters:
;       AH:     UART_LineStatus bit to test (20h for write, or 1h for read)
;               One entry point fills in AH with 20h for write
;       DX:     Port address (OK if already incremented to UART_lineStatus)
;       BX:     
;       Stack:  2 words on the stack below the command/count word
;   Returns:
;       Returns when desired UART_LineStatus bit is cleared
;       Jumps directly to error exit if timeout elapses (and cleans up stack)
;   Corrupts registers:
;       AX
;--------------------------------------------------------------------

SerialServer_WaitAndPoll_SoftDelayTicks   EQU   20

ALIGN JUMP_ALIGN
SerialServer_WaitAndPoll_Write:
        mov     ah,20h
;;; fall-through

ALIGN JUMP_ALIGN
SerialServer_WaitAndPoll_Read:
        push    cx
        push    dx

;
; We first poll in a tight loop, interrupts off, for the next character to come in/be sent
;
        xor     cx,cx
.readTimeoutLoop:
        mov     dl,bh
        in      al,dx
        test    al,ah
        jnz     .readTimeoutComplete
        loop    .readTimeoutLoop

;
; If that loop completes, then we assume there is a long delay involved, turn interrupts back on
; and wait for a given number of timer ticks to pass.
;
        sti
        mov     cl,SerialServer_WaitAndPoll_SoftDelayTicks
%ifndef SERIALSERVER_TIMER_LOCATION
        call    Timer_InitializeTimeoutWithTicksInCL
%else
        push    ax
        push    bx
        mov     ax,SerialServer_WaitAndPoll_SoftDelayTicks
        mov     bx,SERIALSERVER_TIMER_LOCATION
        call    TimerTicks_InitializeTimeoutFromAX
        pop     bx
        pop     ax
%endif
        
.WaitAndPoll:
%ifndef SERIALSERVER_TIMER_LOCATION
        call    Timer_SetCFifTimeout
%else
        push    ax
        push    bx
        mov     bx,SERIALSERVER_TIMER_LOCATION
        call    TimerTicks_GetTimeoutTicksLeftToAXfromDSBX
        pop     bx
        pop     ax
%endif      
        jc      SerialServer_OutputWithParameters_ErrorAndPop4Words
        in      al,dx
        test    al,ah
        jz      .WaitAndPoll
        cli

.readTimeoutComplete:
        pop     dx
        pop     cx
        ret