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+====== silver surfer polling mode driver for cc65 ======
+<code>
+;----------------------------------------------------------------------------------------------
+; silver surfer polling mode driver for cc65
+; - work from here to create a full featured driver with interupts.
+; gpz fixed 20020828: fatal bug fixed in _ss232_params
+;----------------------------------------------------------------------------------------------
+.include "ports/silversurfer.inc"
+                        .export _ss232_init
+                        .export _ss232_done
+                        .export _ss232_params
+                        .export _ss232_put
+                        .export _ss232_get
+                        .importzp ptr1, ptr2
+                        .import   popa, popax
+;----------------------------------------------------------------------------------------------
+; Error codes. Beware: The codes must match the codes in the C header file
+ErrNotInitialized       = $01
+ErrBaudTooFast          = $02
+ErrBaudNotAvail         = $03
+ErrNoData               = $04
+ErrOverflow             = $05
+;----------------------------------------------------------------------------------------------
+;unsigned char __fastcall__ rs232_init (char hacked);
+;/* Initialize the serial port, install the interrupt handler. The parameter
+; * has no effect for now and should be set to 0.
+; */
+;----------------------------------------------------------------------------------------------
+         .code
+_ss232_init:
+         ; enable ssurfer-port
+         lda $de01
+         ora #$01
+         sta $de01
+         ; disable nmi's from ssurfer
+         lda #%00000000
+         sta fifo_ier
+         ; activate dtr
+         lda #%00000001
+         sta fifo_mcr
+         lda #$00       ; ok
+         tax
+         rts
+;----------------------------------------------------------------------------------------------
+;unsigned char __fastcall__ rs232_done (void);
+;/* Close the port, deinstall the interrupt hander. You MUST call this function
+; * before terminating the program, otherwise the machine may crash later. If
+; * in doubt, install an exit handler using atexit(). The function will do
+; * nothing, if it was already called.
+; */
+;----------------------------------------------------------------------------------------------
+_ss232_done:
+         ; disable nmi's from ssurfer
+         lda #%00000000
+         sta fifo_ier
+         ; deactivate dtr
+         sta fifo_mcr
+         ; disable ssurfer-port
+         lda $de01
+         and #$fe
+         sta $de01
+         lda #$00       ; ok
+         tax
+         rts
+;----------------------------------------------------------------------------------------------
+;unsigned char __fastcall__ rs232_params (unsigned char params, unsigned char parity);
+;/* Set the port parameters. Use a combination of the #defined values above. */
+;----------------------------------------------------------------------------------------------
+         .data
+_ss232_baudrates:
+         .word          (7372800 / (      50 * 16))
+         .word          (7372800 / (     110 * 16))
+         .word          (7372800 / (     269 *  8))
+         .word          (7372800 / (     300 * 16))
+         .word          (7372800 / (     600 * 16))
+         .word          (7372800 / (    1200 * 16))
+         .word          (7372800 / (    2400 * 16))
+         .word          (7372800 / (    4800 * 16))
+         .word          (7372800 / (    9600 * 16))
+         .word          (7372800 / (   19200 * 16))
+         .word          (7372800 / (   38400 * 16))
+         .word          (7372800 / (   57600 * 16))
+         .word          (7372800 / (  115200 * 16))
+         .word          (7372800 / (  230400 * 16))
+         .bss
+_ss232_tmp1:
+         .res 1
+         .code
+_ss232_params:
+         sta _ss232_tmp1 ; save parity
+         ; reset fifo
+         lda #%10000111
+         sta fifo_fcr
+   ; that delay thing really needed ?!
+   ; (original datasheet mentions a delay here)
+   ;      ldy #$00
+   ;      dey
+   ;      bny *-1
+         ; set dlab
+         lda #%10000011 ; we assmume 8n1
+         sta fifo_lcr
+         jsr popa
+         tay             ; save param
+         ; set baudrate
+         clc
+         lsr a
+         lsr a
+         lsr a
+         lsr a
+         asl a
+         tax
+         lda _ss232_baudrates,x
+         sta fifo_dll
+         lda _ss232_baudrates+1,x
+         sta fifo_dlm
+         tya             ; param
+         and #$0f
+         ora _ss232_tmp1 ; parity
+         ; reset dlab
+         sta fifo_lcr
+         lda #$00       ; ok
+         tax
+         rts
+;----------------------------------------------------------------------------------------------
+; check if byte available, returns AKKU=0 if none
+ss_getlsr:
+         lda fifo_lsr
+         and #$01
+         rts
+;----------------------------------------------------------------------------------------------
+;unsigned char __fastcall__ rs232_get (char* b);
+;/* Get a character from the serial port. If no characters are available, the
+; * function will return RS_ERR_NO_DATA, so this is not a fatal error.
+; */
+;----------------------------------------------------------------------------------------------
+; get byte (non blocking, returns byte in A or CARRY=1 - error)
+_ss232_get:
+         sta ptr1
+         stx ptr1+1
+         jsr ss_getlsr  ; check if byte available
+;         bne sk32 ; yes
+         bne sk33 ; yes
+         ; activate rts
+         lda #%00000011
+         sta fifo_mcr
+sk32:
+         ; deactivate rts
+;         lda #%00000001
+;         sta fifo_mcr
+         jsr ss_getlsr  ; check if byte available
+         bne sk33 ; yes
+         ; deactivate rts
+         lda #%00000001
+         sta fifo_mcr
+         lda #ErrNoData      ; no data
+         ldx #0
+         rts
+sk33:
+         ; deactivate rts
+         lda #%00000001
+         sta fifo_mcr
+         ; get byte
+         ldy #$00
+         lda fifo_rxd
+         sta (ptr1),y
+         lda #0      ; ok
+         tax
+         rts
+;----------------------------------------------------------------------------------------------
+;unsigned char __fastcall__ rs232_put (char b);
+;/* Send a character via the serial port. There is a transmit buffer, but
+; * transmitting is not done via interrupt. The function returns
+; * RS_ERR_OVERFLOW if there is no space left in the transmit buffer.
+; */
+;----------------------------------------------------------------------------------------------
+_ss232_put:
+         tax
+         ; transmit buf ready?
+         lda fifo_lsr
+         and #%00100000
+         bne @sk1
+@sk2:
+         lda #ErrOverflow       ; overflow
+         ldx #$00
+         rts
+@sk1:
+         ; reciever ready?
+         lda fifo_msr
+         and #%00010000
+         beq @sk2
+         stx fifo_txd
+         lda #$00               ; ok
+         tax
+         rts
+;----------------------------------------------------------------------------------------------
+;unsigned char __fastcall__ rs232_pause (void);
+;/* Assert flow control and disable interrupts. */
+;----------------------------------------------------------------------------------------------
+_ss232_pause:
+         ; activate rts
+         lda #%00000011
+         sta fifo_mcr
+         lda #$00       ; ok
+         tax
+         rts
+;----------------------------------------------------------------------------------------------
+;unsigned char __fastcall__ rs232_unpause (void);
+;/* Re-enable interrupts and release flow control */
+;----------------------------------------------------------------------------------------------
+_ss232_unpause:
+         ; deactivate rts
+         lda #%00000001
+         sta fifo_mcr
+         lda #$00       ; ok
+         tax
+         rts
+;----------------------------------------------------------------------------------------------
+;unsigned char __fastcall__ rs232_status (unsigned char* status,
+;                                         unsigned char* errors);
+;/* Return the serial port status. */
+;----------------------------------------------------------------------------------------------
+_ss232_status:
+        sta     ptr2
+        stx     ptr2+1
+        jsr     popax
+        sta     ptr1
+        stx     ptr1+1
+        ldy     #$00
+        ; Get status
+        lda     fifo_iir
+        and     #%00000001
+        sta     _ss232_tmp1
+        lda     fifo_msr
+        lsr     a
+        and     #%01010000
+        ora     _ss232_tmp1
+        sta     _ss232_tmp1
+        lda     fifo_lsr
+        and     #%00101110
+        ora     _ss232_tmp1
+        sta     (ptr1),y
+        ; Get errors
+        lda     #$00    ; ok
+        sta     (ptr2),y
+        lda     #$00    ; ok
+        tax
+        rts
+</code>