source: xtideuniversalbios/trunk/Assembly_Library/Src/Serial/SerialServerScan.asm@ 369

; Project name  :   Assembly Library
; Description   :   Serial Server Support, Scan for Server
;
; This functionality is broken out from SerialServer as it may only be needed during
; initialization to find a server, and then could be discarded, (for example the case
; of a TSR).

%include "SerialServer.inc"
        
; Section containing code
SECTION .text
        
;--------------------------------------------------------------------
; SerialServerScan_ScanForServer:   
;   Parameters:
;       BH:     Drive Select byte for Drive and Head Select Register
;               0xAx: Scan for drive, low nibble indicates drive
;               0x0:  Scan for Server, independent of drives
;       DX:     Port and Baud to Scan for
;               0: Scan a known set of ports and bauds
;       ES:SI:  Ptr to buffer for return
;   Returns:
;       CF:     Cleared if success, Set if error
;   Corrupts registers:
;       AL, BX, CX, DX, DI
;--------------------------------------------------------------------
SerialServerScan_ScanForServer:     
        mov     cx, 1           ; one sector, not scanning (default)

        test    dx, dx
        jnz     short SerialServerScan_CheckForServer_PortAndBaudInDX

        mov     di,.scanPortAddresses-1
        mov     ch,1            ;  tell server that we are scanning

.nextPort:
        inc     di              ; load next port address
        xor     dh, dh
        mov     dl,[cs:di]
        eSHL_IM dx, 2           ; shift from one byte to two
        stc                     ; setup error code for exit
        jz      .error

;
; Test for COM port presence, write to and read from registers
;
        push    dx
        add     dl,Serial_UART_lineControl
        mov     al, 09ah
        out     dx, al
        in      al, dx
        pop     dx
        cmp     al, 09ah
        jnz     .nextPort

        mov     al, 0ch
        out     dx, al
        in      al, dx
        cmp     al, 0ch
        jnz     .nextPort

;
; Begin baud rate scan on this port...
;
; On a scan, we support 6 baud rates, starting here and going higher by a factor of two each step, with a
; small jump between 9600 and 38800.  These 6 were selected since we wanted to support 9600 baud and 115200,
; *on the server side* if the client side had a 4x clock multiplier, a 2x clock multiplier, or no clock multiplier.
;
; Starting with 30h, that means 30h (2400 baud), 18h (4800 baud), 0ch (9600 baud), and
;                               04h (28800 baud), 02h (57600 baud), 01h (115200 baud)
;
; Note: hardware baud multipliers (2x, 4x) will impact the final baud rate and are not known at this level
;
        mov     dh,030h * 2     ; multiply by 2 since we are about to divide by 2
        mov     dl,[cs:di]      ; restore single byte port address for scan

.nextBaud:
        shr     dh,1
        jz      .nextPort
        cmp     dh,6            ; skip from 6 to 4, to move from the top of the 9600 baud range
        jnz     .testBaud       ; to the bottom of the 115200 baud range
        mov     dh,4

.testBaud:
        call    SerialServerScan_CheckForServer_PortAndBaudInDX
        jc      .nextBaud

.error: 
        ret

.scanPortAddresses: db  SERIAL_COM7_IOADDRESS >> 2
                    db  SERIAL_COM6_IOADDRESS >> 2
                    db  SERIAL_COM5_IOADDRESS >> 2
                    db  SERIAL_COM4_IOADDRESS >> 2
                    db  SERIAL_COM3_IOADDRESS >> 2
                    db  SERIAL_COM2_IOADDRESS >> 2
                    db  SERIAL_COM1_IOADDRESS >> 2
                    db  0
        

;--------------------------------------------------------------------
; SerialServer_CheckForServer_PortAndBaudInDX:
;   Parameters:
;       BH:     Drive Select byte for Drive and Head Select Register
;               0xAx: Scan for drive, low nibble indicates drive
;               0x0:  Scan for Server, independent of drives
;       DX:     Baud and Port
;       CH:     1: We are doing a scan for the serial server
;               0: We are working off a specific port given by the user
;       CL:     1, for one sector to read
;       ES:SI:  Ptr to buffer for return
;   Returns:
;       AH:     INT 13h Error Code
;       CF:     Cleared if success, Set if error
;   Corrupts registers:
;       AL, BX
;--------------------------------------------------------------------
SerialServerScan_CheckForServer_PortAndBaudInDX:
        push    bp              ; setup fake SerialServer_Command

        push    dx              ; send port baud and rate, returned in inquire packet
                                ; (and possibly returned in the drive identification string)

        push    cx              ; send number of sectors, and if it is on a scan or not

        mov     bl,SerialServer_Command_Inquire         ; protocol command onto stack with bh
        push    bx

        mov     bp,sp
        
        call    SerialServer_SendReceive

        pop     bx
        pop     cx
        pop     dx
        pop     bp

        ret