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/serial.asm
0,0 → 1,340
; ============================================================================
; __
; \\__/ o\ (C) 2022 Robert Finch, Waterloo
; \ __ / All rights reserved.
; \/_// robfinch<remove>@opencores.org
; ||
;
;
; Serial port routines for a WDC6551 compatible circuit.
;
; This source file is free software: you can redistribute it and/or modify
; it under the terms of the GNU Lesser General Public License as published
; by the Free Software Foundation, either version 3 of the License, or
; (at your option) any later version.
;
; This source file is distributed in the hope that it will be useful,
; but WITHOUT ANY WARRANTY; without even the implied warranty of
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
; GNU General Public License for more details.
;
; You should have received a copy of the GNU General Public License
; along with this program. If not, see <http://www.gnu.org/licenses/>.
;
; ============================================================================
;
;------------------------------------------------------------------------------
; Initialize serial port.
;
; Clear buffer indexes. Two bytes are used for the buffer index even though
; only a single byte is needed. This is for convenience in calculating the
; number of characters in the buffer, done later. The upper byte remains at
; zero.
; The port is initialized for 9600 baud, 1 stop bit and 8 bits data sent.
; The internal baud rate generator is used.
;
; Parameters:
; none
; Modifies:
; d
; Returns:
; none
;------------------------------------------------------------------------------
 
InitSerial:
SerialInit:
clra
clrb
std SerHeadRcv-1
std SerTailRcv-1
std SerHeadXmit-1
std SerTailXmit-1
clr SerRcvXon
clr SerRcvXoff
lda COREID
sini1:
cmpa IOFocusID
bne sini1
ldb #$09 ; dtr,rts active, rxint enabled, no parity
stb ACIA+ACIA_CMD
ldb #$1E ; baud 9600, 1 stop bit, 8 bit, internal baud gen
stb ACIA+ACIA_CTRL
ldb #$0A6 ; diable fifos, reset fifos
stb ACIA+ACIA_CTRL2
rts
 
;------------------------------------------------------------------------------
; SerialGetChar
;
; Check the serial port buffer to see if there's a char available. If there's
; a char available then return it. If the buffer is almost empty then send an
; XON.
;
; Stack Space:
; 2 words
; Parameters:
; none
; Modifies:
; none
; Returns:
; d = character or -1
;------------------------------------------------------------------------------
 
SerialGetChar:
pshs x,y
ldy #0
sei ; disable interrupts
bsr SerialRcvCount ; check number of chars in receive buffer
cmpb #8 ; less than 8?
bhi sgc2
ldb SerRcvXon ; skip sending XON if already sent
bne sgc2 ; XON already sent?
ldb #XON ; if <8 send an XON
clr SerRcvXoff ; clear XOFF status
stb SerRcvXon ; flag so we don't send it multiple times
bsr SerialPutChar
sgc2:
ldb SerHeadRcv ; check if anything is in buffer
cmpb SerTailRcv
beq sgcNoChars ; no?
ldx #SerRcvBuf
clra
ldb b,x ; get byte from buffer
inc SerHeadRcv ; 4k wrap around
bra sgcXit
sgcNoChars:
ldd #-1
sgcXit:
cli
puls x,y,pc
 
;------------------------------------------------------------------------------
; SerialPeekChar
;
; Check the serial port buffer to see if there's a char available. If there's
; a char available then return it. But don't update the buffer indexes. No need
; to send an XON here.
;
; Stack Space:
; 0 words
; Parameters:
; none
; Modifies:
; none
; Returns:
; d = character or -1
;------------------------------------------------------------------------------
 
SerialPeekChar:
pshs x,ccr
sei
ldb SerHeadRcv ; check if anything is in buffer
cmpb SerTailRcv
beq spcNoChars ; no?
ldx #SerRcvBuf
clra
ldb b,x ; get byte from buffer
bra spcXit
spcNoChars:
ldd #-1
spcXit:
puls x,ccr,pc
 
;------------------------------------------------------------------------------
; SerialPeekChar
; Get a character directly from the I/O port. This bypasses the input
; buffer.
;
; Stack Space:
; 0 words
; Parameters:
; none
; Modifies:
; d
; Returns:
; d = character or -1
;------------------------------------------------------------------------------
 
SerialPeekCharDirect:
lda COREID ; Ensure we have the IO Focus
cmpa IOFocusID
bne spcd0001
; Disallow interrupts between status read and rx read.
sei
ldb ACIA+ACIA_STAT
bitb #8 ; look for Rx not empty
beq spcd0001
clra
ldb ACIA+ACIA_RX
cli
rts
spcd0001:
ldd #-1
cli
rts
 
;------------------------------------------------------------------------------
; SerialPutChar
; Put a character to the serial transmitter. This routine blocks until the
; transmitter is empty.
;
; Stack Space
; 0 words
; Parameters:
; b = character to put
; Modifies:
; none
;------------------------------------------------------------------------------
 
SerialPutChar:
pshs a,ccr
spc0001:
lda COREID ; Ensure we have the IO Focus
cmpa IOFocusID
bne spc0001
cli ; provide a window for an interrupt to occur
sei
; Between the status read and the transmit do not allow an
; intervening interrupt.
lda ACIA+ACIA_STAT ; wait until the uart indicates tx empty
bita #16 ; bit #4 of the status reg
beq spc0001 ; branch if transmitter is not empty
stb ACIA+ACIA_TX ; send the byte
puls a,ccr,pc
 
;------------------------------------------------------------------------------
; Calculate number of character in input buffer
;
; Parameters:
; y = 0 if current core, otherwise reference to core memory area $Cyxxxx
; Returns:
; d = number of bytes in buffer.
;------------------------------------------------------------------------------
 
SerialRcvCount:
clra
ldb SerTailRcv,y
subb SerHeadRcv,y
bge srcXit
ldd #$1000
subd SerHeadRcv,y
addd SerTailRcv,y
srcXit:
rts
 
;------------------------------------------------------------------------------
; Serial IRQ routine
;
; Keeps looping as long as it finds characters in the ACIA recieve buffer/fifo.
; Received characters are buffered. If the buffer becomes full, new characters
; will be lost.
;
; Parameters:
; none
; Modifies:
; d,x
; Returns:
; none
;------------------------------------------------------------------------------
 
SerialIRQ:
sirqNxtByte:
ldb ACIA+ACIA_STAT ; check the status
bitb #$08 ; bit 3 = rx full
beq notRxInt
ldb ACIA+ACIA_RX ; get data from Rx buffer to clear interrupt
cmpb #CTRLT ; detect special keystroke
bne sirq0001
; bsr DumpTraceQueue
sirq0001:
pshs b
; Compute receive buffer address
lda IOFocusID
asla
asla
asla
asla
ora #$C00
clrb
tfr d,y
puls b
lda SerTailRcv,y ; check if recieve buffer full
inca
cmpa SerHeadRcv,y
beq sirqRxFull
sta SerTailRcv,y ; update tail pointer
deca ; backup
exg a,b
leax SerRcvBuf,y ; x = buffer address
sta b,x ; store recieved byte in buffer
tst SerRcvXoff,y ; check if xoff already sent
bne sirqNxtByte
bsr SerialRcvCount ; if more than 4080 chars in buffer
cmpb #4080
blo sirqNxtByte
ldb #XOFF ; send an XOFF
clr SerRcvXon,y ; clear XON status
stb SerRcvXoff,y ; set XOFF status
stb ACIA+ACIA_TX
bra sirqNxtByte ; check the status for another byte
sirqRxFull:
notRxInt:
rts
 
nmeSerial:
fcb "Serial",0
 
;------------------------------------------------------------------------------
; Put a string to the serial port.
;
; Parameters:
; d = pointer to string
; Modifies:
; none
; Returns:
; none
;------------------------------------------------------------------------------
 
SerialPutString:
pshs d,x
tfr d,x
sps2:
ldb ,x
beq spsXit
inx
bsr SerialPutChar
bra sps2
spsXit:
puls d,x,pc
 
;------------------------------------------------------------------------------
; A little routine to test serial output.
;
; Parameters:
; none
; Modifies:
; none
; Returns:
; none
;------------------------------------------------------------------------------
 
SerialOutputTest:
pshs d
ldd #msgSerialTest
lbsr DisplayString
bsr SerialInit
sotst1:
ldb #XON
bsr SerialPutChar
bsr SerialPutChar
bsr SerialPutChar
ldd #msgSerialTest
bsr SerialPutString
lbsr INCH
cmpb #CTRLC
bne sotst1
puls d,pc
 
msgSerialTest:
fcb "Serial port test",CR,LF,0
 

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