Category : C Source Code
Archive   : BOOKCOMM.ZIP
Filename : SERASM.ASM

;
; serasm.asm - Low Level Communcations Routines
; Copyright (c) 1992 by Mark Goodwin
;

;
; UART register constants
;
IIR equ 2
MCR equ 4
LSR equ 5
MSR equ 6

;
; UART bit mask constants
;
RX_RDY equ 1
TX_RDY equ 20H
INT_MASK equ 7
RX_ID equ 4
MC_INT equ 8
DTR equ 1
RTS equ 2
CTS equ 10H
DSR equ 20H
DCD equ 80H
ICR equ 20H
EOI equ 20H

;
; XON/XOFF constants
;
XON equ 11H
XOFF equ 13H

;
; system clock location
;
CLOCK equ 46cH

;
; boolean values
;
TRUE equ 1
FALSE equ 0

;
; data segment
;
DGROUP group _DATA
_DATA segment word public 'DATA'
assume ds:DGROUP

;
; declare all variables as public
;
public _sibuff,_eibuff,_ilen,_inbuff
public _rx_flow,_rx_rts,_rx_dtr,_rx_xon
public _tx_rts,_tx_dtr,_tx_xon,_tx_xonoff
public _fon,_foff
public _base

;
; varibles
;
_sibuff dw ? ;start of input buffer ptr
_eibuff dw ? ;end of input buffer ptr
_ilen dw ? ;input buffer length
_inbuff dd ? ;input buffer ptr
_rx_flow dw ? ;input buffer full flag
_rx_rts dw ? ;receive RTS/CTS flag
_rx_dtr dw ? ;receive DTR/DSR flag
_rx_xon dw ? ;receive XON/XOFF flag
_tx_rts dw ? ;xmit RTS/CTS flag
_tx_dtr dw ? ;xmit DTR/DSR flag
_tx_xon dw ? ;xmit XON/XOFF flag
_tx_xonoff dw ? ;xmit XOFF flag
_fon dw ? ;point to turn receive flow on
_foff dw ? ;point to turn receive flow off
_base dw ? ;UART base ptr

_DATA ends

;
; code segment
;
SERASM_TEXT segment para public 'CODE'
assume cs:SERASM_TEXT

;
; declare procedures public
;
public _get_serial,_put_serial,_handler,_mpeek

;
; get character from the serial port
;
_get_serial proc far
push di ;save di
push es ;save es
mov ax,-1 ;ax=character not available
push ax ;save it on stack
mov bx,_sibuff ;bx=next character ptr
cmp bx,_eibuff ;buffer empty?
je gs4 ;jump if it is
pop ax ;remove dummy return value
les di,_inbuff ;es:di=input buffer ptr
mov al,es:[di][bx] ;al=next character
xor ah,ah ;ax=next character
push ax ;save it on stack
inc bx ;bump the next character ptr
cmp bx,_ilen ;wrap ptr?
jne gs1 ;jump if not
xor bx,bx ;point it to start of buffer
gs1: mov _sibuff,bx ;save the new ptr
cmp _rx_flow,TRUE ;receive flow?
jne gs4 ;jump if not
call chars_in_buff ;ax=number of chars in buffer
cmp ax,_fon ;turn back on?
jg gs4 ;jump if not
mov _rx_flow,FALSE ;flag receive flow off
cmp _rx_rts,TRUE ;RTS/CTS?
jne gs2 ;jump if not
mov dx,_base ;dx=base ptr
add dx,MCR ;dx=modem control register
in al,dx ;get current value
or al,RTS ;assert RTS
out dx,al ;send new value to UART
gs2: cmp _rx_dtr,TRUE ;DTR/DSR?
jne gs3 ;jump if not
mov dx,_base ;dx=base ptr
add dx,MCR ;dx=modem control register
in al,dx ;get current value
or al,DTR ;assert DTR
out dx,al ;send new value to UART
gs3: cmp _rx_xon,TRUE ;XON/XOFF?
jne gs4 ;Jump if not
cli ;disable the interrupts
mov dx,_base ;dx=xmit register
mov al,XON ;al=XON value
out dx,al ;send it to remote
sti ;enable the interrupts
gs4: pop ax ;get the character
pop es ;restore es
pop di ;restore di
ret ;return
_get_serial endp

;
; send a byte out through the serial port
;
_put_serial proc far
char equ <[bp + 6]> ;char parameter
push bp ;save bp
mov bp,sp ;bp=stack frame ptr
push di ;save di
push es ;save es
xor ax,ax ;ax=segment 0000h
mov es,ax ;es=segment 0000h ptr
mov di,CLOCK ;es:di=system clock ptr
mov bx,es:[di] ;bx=current value
mov cx,18 ;cx=1 second timeout value
mov dx,_base ;dx=base register
mov dx,MCR ;dx=modem control register
in al,dx ;al=current value
or al,MC_INT or DTR or RTS ;assert GPO2, DTR, RTS
out dx,al ;send it to UART
cmp _tx_rts,TRUE ;RTS/CTS?
jne ps2 ;Jump if not
mov dx,_base ;dx=base register
add dx,MSR ;dx=modem status register
ps1: in al,dx ;al=current value
and al,CTS ;CTS asserted?
jnz ps2 ;jump if it is
cmp bx,es:[di] ;system clock changed?
je ps1 ;loop if not
mov bx,es:[di] ;bx=new system clock value
loop ps1 ;loop till time out
jmp ps9 ;jump for time out
ps2: cmp _tx_dtr,TRUE ;DTR/DSR?
jne ps4 ;jump if not
mov dx,_base ;dx=base register
add dx,MSR ;dx=modem status register
ps3: in al,dx ;al=current value
and al,DSR ;DSR asserted?
jnz ps4 ;jump if it is
cmp bx,es:[di] ;system clock changed?
je ps3 ;loop if not
mov bx,es:[di] ;bx=new system clock value
loop ps3 ;loop till time out
jmp ps9 ;jump for time out
ps4: cmp _tx_xon,TRUE ;XON/XOFF?
jne ps6 ;jump if not
ps5: cmp _tx_xonoff,TRUE ;XOFF?
jne ps6 ;jump if not
mov dx,_base ;dx=base register
add dx,MSR ;dx=modem status register
in al,dx ;al=current value
and al,DCD ;carrier?
jnz ps5 ;loop if it is
ps6: mov dx,_base ;dx=base register
add dx,LSR ;dx=line status register
ps7: in al,dx ;al=current value
and al,TX_RDY ;xmitter ready?
jnz ps8 ;jump if it is
cmp bx,es:[di] ;system clock changed?
je ps3 ;loop if not
mov bx,es:[di] ;bx=new system clock value
loop ps7 ;loop till time out
jmp ps9 ;jump for time out
ps8: cli ;disable the interrupts
mov dx,_base ;dx=xmitter register
mov ax,char ;al=character to send
out dx,al ;send it
sti ;enable the interrupts
ps9: pop es ;restore es
pop di ;restore di
mov sp,bp ;restore the stack ptr
pop bp ;restore bp
ret ;return
_put_serial endp

;
; calculate number of character in input buffer
;
chars_in_buff proc near
mov ax,_eibuff ;ax=end of buffer ptr
sub ax,_sibuff ;figure number of chars
jae cib1 ;jump if ptrs haven't crossed
mov ax,_ilen ;ax=buffer size
sub ax,_sibuff ;ax=number chars to end of buffer
add ax,_eibuff ;ax=number chars in buffer
cib1: ret ;return
chars_in_buff endp

;
; interrupt handler
;
_handler proc far
push ax ;save ax
push bx ;save bx
push cx ;save cx
push dx ;save dx
push si ;save si
push di ;save di
push bp ;save bp
push es ;save es
push ds ;save ds
mov ax,seg _base ;ax=segment address
mov ds,ax ;ds=segment address
mov dx,_base ;dx=base register
add dx,IIR ;dx=interrupt id register
in al,dx ;al=current value
and al,INT_MASK ;mask it
cmp al,RX_ID ;receive interrupt?
je h1 ;jump if it is
jmp h8 ;jump if not
h1: mov dx,_base ;dx=receive register
in al,dx ;al=new character
cmp _tx_xon,TRUE ;XON/XOFF?
jne h3 ;jump if not
cmp al,XOFF ;XOFF?
jne h2 ;jump if not
mov _tx_xonoff,TRUE ;flag XOFF
jmp h5 ;jump
h2: cmp al,XON ;XON?
jne h3 ;jump if not
mov _tx_xonoff,FALSE ;flag not XOFF
jmp h5 ;jump
h3: mov _tx_xonoff,FALSE ;flag not XOFF
mov bx,_eibuff ;bx=next char ptr
les di,_inbuff ;es:di=input buffer ptr
mov es:[di][bx],al ;save the char
inc bx ;bump the buffer ptr
cmp bx,_ilen ;wrap it?
jne h4 ;jump if not
xor bx,bx ;point to start of buffer
h4: mov _eibuff,bx ;save new ptr
h5: mov dx,_base ;dx=base register
add dx,LSR ;dx=line status register
in al,dx ;al=current value
and al,RX_RDY ;another character available
jnz h1 ;loop if it is
cmp _rx_flow,TRUE ;receive flow on?
je h8 ;jump if it is
call chars_in_buff ;ax=no chars in buffer
cmp ax,_foff ;turn receive off?
jb h8 ;jump if not
mov _rx_flow,TRUE ;flag receive flow on
cmp _rx_rts,TRUE ;RTS/CTS?
jne h6 ;jump if not
mov dx,_base ;dx=base register
add dx,MCR ;dx=modem control register
in al,dx ;al=current value
and al,not RTS ;unassert RTS
out dx,al ;send it to UART
h6: cmp _rx_dtr,TRUE ;DTR/DSR?
jne h7 ;jump if not
mov dx,_base ;dx=base register
add dx,MCR ;dx=modem control register
in al,dx ;al=current value
and al,not DTR ;unassert DTR
out dx,al ;send it to UART
h7: cmp _rx_xon,TRUE ;XON/XOFF?
jne h8 ;jump if not
mov dx,_base ;dx=xmit register
mov al,XOFF ;al=XOFF
out dx,al ;send it
h8: mov dx,ICR ;dx=interrupt control register
mov al,EOI ;al=end of interrupt command
out dx,al ;send it
pop ds ;restore ds
pop es ;restore es
pop bp ;restore bp
pop di ;restore di
pop si ;restore si
pop dx ;restore dx
pop cx ;restore cx
pop bx ;restore bx
pop ax ;restore ax
iret ;return
_handler endp

;
; get word of memory routine
;
_mpeek proc far
srcseg equ <[bp + 6]> ;segment parameter
srcoff equ <[bp + 8]> ;offset parameter
push bp ;save bp
mov bp,sp ;bp=stack frame ptr
push di ;save di
push es ;save es
mov es,srcseg ;es=segment address
mov di,srcoff ;di=offset address
mov ax,es:[di] ;ax=memory word
pop es ;restore es
pop di ;restore di
pop bp ;restore bp
ret ;return;
_mpeek endp


SERASM_TEXT ends

end