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Assembly Source File | 1986-02-10 | 47KB | 1,847 lines

title 'LEVEL2.ASM' ;************************************************ ;* * ;* LEVEL2.ASM * ;* * ;* X.25 level 2 (HDLC) protocol handler * ;* (note that some level2 real time tasks, * ;* such as flag generation/detection, bit * ;* stuffing/stripping and CRC generation/ * ;* checking are handled by the Level 1 * ;* hardware (SIO)) * ;* * ;* rev 1.52 08/08/84 E. Elizondo * ;* * ;* (c) 1984 E. Elizondo - all rights reserved. * ;* * ;* This program may be used freely for non- * ;* commercial applications. It may not be sold * ;* or used for commercial applications without * ;* written permission of the author. * ;* * ;************************************************ ; maclib Z80 ;DR Z80 macro library ; assembly time options false equ 0 true equ not false debug equ true ;display V(s) of tx I frames ; design parameters kconst equ 4 ;max # of unack. frames n2 equ 10 ;max # of re-transmissions kack equ 10 ;acknowledgement delay count ; X.25 standard parameters: ; frame addresses (X.25 para 2.4.1) ; bit # 8765$4321 addra equ 0000$0011b ;address A addrb equ 0000$0001b ;address B ; frame control (id) bytes (table 3/X.25) ; bit # 8765$4321 ifid equ 0000$0000b ;I rrfid equ 0000$0001b ;RR rnrfid equ 0000$0101b ;RNR rejfid equ 0000$1001b ;REJ sarmfid equ 0000$1111b ;SARM (not used in LAPB) dmfid equ 0000$1111b ;DM sabmfid equ 0010$1111b ;SABM discfid equ 0100$0011b ;DISC uafid equ 0110$0011b ;UA cmdrfid equ 1000$0111b ;CMDR frmrfid equ 1000$0111b ;FRMR badfid equ 1111$1111b ;bad frame for testing ; misc constants cr equ 0dh ;carriage ret lf equ 0ah ;line feed tab equ 09h ;horizontal tab ; hooks for other modules ; subroutines public initl2 ;initialize level 2 parameters public rxfrm ;process a received frame public txifrm ;transmit I frame if avail public conlk ;connect link public disclk ;disconnect link public qlksta ;query link status public gettxb ;get address of free tx bcb public txbadf ;transmit bad frame ; addresses public lkstat ;level 2 link status bits public l2stat ;level 2 status bits public dtemod ;DTE/DCE mode flag ; level 2 parameters public vs ;V(s) public vr ;V(r) public lastnr ;last received N(r) public lastvr ;last transmitted V(r) public lastvs ;last transmitted V(s) public maxvs ;highest tx V(s) public pfbit ;P/F bit ; diagnostic counters public rxifct ;received I frame count public rxcfct ;received cmd frames public rxrfct ;received resp frames public rbafct ;received bad addr frames public rxbcct ;received bad cmd frames public rxbrct ;received bad rsp frames public txfct ;transmitted frame count public txifct ;transmitted I frame count public txirct ;tx I retransmission log ; definition of lkstat status bits ; (note DTE busy comes from level1) ; bit set condition ; 0 link connect in process ; 1 link disconnect in process ; 2 link connected ; 3 DCE busy ; 4 DTE busy ; 5 unassigned ; 6 DTE REJ condition ; 7 DCE REJ condition ; definition of l2stat status bits ; bit set condition ; 0 link query in process ; 1 DTE FRMR condition ; 2 DCE FRMR condition ; 3 unassigned ; 4 unassigned ; 5 unassigned ; 6 retransmit old I frame ; 7 timer recovery condition ; external subroutines ; from buffers module: extrn inibuf ;initialize all buffers extrn putbuf ;put char in buffer extrn getbuf ;get char from buffer extrn dcrbuf ;delete last char in buffer extrn bpoint ;point to selected bcb extrn rlsrxb ;release rx buffer extrn clrbuf ;clear buffer for new use extrn clrtxb ;clear all tx buffers extrn savbcb ;save bcb pointers extrn getbct ;get buffer count extrn getrdy ;get state of buffer ready flag ; from level1 module: extrn txwake ;wake up transmitter extrn t1on ;turn on timer T1 extrn t1off ;turn off timer T1 ; from level 3 module: extrn initl3 ;initialize level 3 extrn txstar ;transmit restart packet ; ; from xutil module: extrn ilprt ;in line print routine extrn pdec ;print <hl> in decimal extrn phex ;print <a> in hex extrn pbin ;print <a> in binary extrn ctype ;print ASCII char in <a> extrn poll ;poll non-interrupt hardware ; from files module extrn fstat ;file status flags extrn ctxfil ;close transmit file extrn crxfil ;close receive file extrn logdat ;write byte to log file ; external addresses ; from level 1 module extrn tistat ;timer status flags extrn txstat ;transmit status flags extrn txaddr ;transmit address byte extrn txctrl ;transmit control byte ; from buffers module extrn rxfree ;A(list of free rx buffer #'s) extrn rxflst ;A(list of rx frame buffer #'s) extrn rxplst ;A(list of rx packt buffer #'s) extrn rxbtab ;A(table of rx bcb pointers) extrn txbtab ;A(table of tx bcb pointers) extrn txbcbp ;A(active tx bcb for I frames) extrn txubcb ;A(tx bcb for CMDR frames) ; from files module extrn fstat ;file status ; ********************************* ; * initialization section * ; ********************************* cseg ;code section ; initialize level 2 parameters ; (externally called) ; on entry: no parameters ; on exit: all flags, regs clobbered initl2: lda dtemod ;get mode flag cpi 1 ;DTE mode? jnz init1 ;no, keep going ; ; initialize in DTE mode mvi a,addra ;yes, set up address=A sta rxcaddr ;for incoming commands sta txraddr ;and outgoing responses mvi a,addrb ;set up address=B sta txcaddr ;for outgoing commands sta rxraddr ;and incoming responses jmp init3 ;and continue ; init1: cpi 2 ;DCE mode? jnz init2 ;no, keep going ; ; initialize as DCE mvi a,addrb ;set up address=B sta rxcaddr ;for incoming commands sta txraddr ;and outgoing responses mvi a,addra ;set up address=A sta txcaddr ;for outgoing commands sta rxraddr ;and incoming responses jmp init3 ;and conitnue ; ; initialize for self test (with loopback connector) init2: mvi a,addra ;set up address=A sta rxcaddr ;for incoming commands sta txcaddr ;and outgoing commands mvi a,addrb ;set up address=B sta txraddr ;for outgoing responses sta rxraddr ;and incoming responses ; init3: call reset ;reset all variables xra a ;reset p/f bit sta pfbit ;p/f=0 ret ; reset all flow control variables ; (internally called) ; on entry: no parameters ; on exit: <a>,flags clobbered reset: xra a ;initialize variables sta vs ;V(s)=0 sta vr ;V(r)=0 sta l2stat ;clear level 2 status flags sta lkstat ;clear link status word sta tistat ;clear all timeouts sta lastnr ;last received N(r) sta lastvr ;last transmitted V(r) mvi a,7 ;initialize... sta lastvs ;last transmitted V(s) sta maxvs ;max transmitted V(s) call clrtxb ;clear all tx buffers ret ; ************************* ; * link control section * ; ************************* ; connect level 2 link ; (externally called) ; on entry: no paramters ; on exit: all regs, flags clobbered conlk: call reset ;reset all flow control variables call initl3 ;initialize level 3 lxi h,lkstat ;point to link status word setb 0,m ;set link connect in process mvi a,n2 ;set retry counter=n2 sta rtryct ; / call ilprt ;tell what's doing db cr,lf,'L2: attempting link connect...',cr,lf,0 jmp txsabm ;and transmit SABM command ; disconnect level 2 link ; (externally called) ; on entry: no paramters ; on exit: all regs, flags clobbered disclk: call crxfil ;close receive file if open call ctxfil ;close receive file if open call clrtxb ;clear all tx I buffers lxi h,lkstat ;point to link status res 1,m ;clear disc in process bit 2,m ;is link connected? jnz disc1 ;yes, keep going ; call ilprt ;else tell operator db 'L2: link is already disconnected',cr,lf,0 ret ; disc1: setb 1,m ;signal disc in process mvi a,n2 ;set retry count= n2 sta rtryct ; / call ilprt ;and tell operator db cr,lf,'L2: attempting link disconnect...',cr,lf,0 jmp txdisc ;and transmit disconnect command ; query link status ; (externally called) ; on entry: no parameters ; on exit: all regs, flags clobbered qlksta: lxi h,lkstat ;point to link status word bit 2,m ;link connected? jnz qlk1 ;yes, keep going ; call ilprt ;else tell operator db 'L2: dte link is disconnected',cr,lf,0 ret ; ; determine dte status qlk1: push h ;save <hl> lxi h,l2stat ;point to flow status word bit 1,m ;DTE FRMR/CMDR condition? pop h ;restore <hl> jz qlk2 ;no, keep going ; call ilprt ;else tell operator db 'L2: dte in FRMR/CMDR condition',cr,lf,0 jmp qlk5 ;and get dce status ; qlk2: bit 4,m ;dte busy? jz qlk3 ;no, keep going ; call ilprt ;else tell operator db 'L2: dte busy',cr,lf,0 jmp qlk5 ;and get dce status ; qlk3: bit 6,m ;dte reject condition? jz qlk4 ;no, keep going ; call ilprt ;else tell operator db 'L2: dte in REJ condition',cr,lf,0 jmp qlk5 ;and get dce status ; qlk4: call ilprt ;tell operator we are ready db 'L2: dte ready',cr,lf,0 ; interogate DCE status qlk5: lxi h,l2stat ;point to level 2 status setb 0,m ;signal query in process mvi a,n2 ;set retry count =n2 sta rtryct ; / call ilprt ;tell operator db 'L2: interrogating dce status...',cr,lf,0 ; ; return here for retries qdce: lxi h,pfbit ;set p=1 setb 4,m ; / lxi h,lkstat ;point to link status bit 4,m ;dte busy? jnz txrnrc ;yes, transmit RNR command ; bit 6,m ;dte rej condition? jnz txrejc ;yes, transmit REJ command ; jmp txrrc ;else transmit RR command ; ************************* ; * transmit section * ; ************************* ; *** miscellaneous *** ; get address of free tx buffer bcb ; (externally called) ; on entry: no parameters ; on exit: carry set if no free buffer avail ; <hl>= bcb address if buffer avail ; <a>, other flags clobbered gettxb: push b ;save regs push d ; / lda lastnr ;get last acknowledged N(r) dcr a ;back up two, mod 7 dcr a ; / ani 7 ; / mov b,a ; is last possible bcb # lda maxvs ;<a> is first possible bcb # inr a ; / ani 7 ; / gettx1: cmp b ;are they equal? stc ;yes, return with carry set jz getxit ; / ; lxi h,txbtab ;else, get bcb address call bpoint ; / call getrdy ;is buffer empty? jz getxok ;yes, got one ; inr a ;else, look at next one ani 7 ;mod 7, of course jmp gettx1 ; / ; getxok: stc ;clear carry flag cmc ; / getxit: pop d ;restore regs pop b ; / ret ; *** outgoing commands *** ; check for timeout condition and ; transmit I frame if available and ; a) link connected ; b) DCE not busy ; c) level 1 (SIO) not already transmitting ; d) not in FRMR condition ; e) new frame within window ; f) frame ready flag <>0 ; if I frame can't be transmitted, transmit ; RR or RNR frame to acknowledge received I frames ; ; (externally called) ; on entry: no parameters ; on exit: all regs, flags clobbered txifrm: ; check for level 1 ready lxi h,txstat ;point to level 1 (SIO) status bit 0,m ;tx busy? rnz ;yes, try again later ; ; check for timeout lxi h,tistat ;point to timer status bit 0,m ;timer T1 timed out? jnz t1to ;yes, service it ; ; check for level 2 ready lxi h,lkstat ;point to link status bit 2,m ;link connected? rz ;no, return ; ; check if in timer recovery condition lxi h,l2stat ;point to flow status bit 7,m ;timer recovery condition? jz txi1 ;no, keep going ; ; timer recovery condition push h ;save flow status word lxi h,pfbit ;set P=1 setb 4,m ; / pop h ;restore flow status word bit 6,m ;time to transmit again? jz txack ;no, see if we want to acknowledge ; bit 2,m ;DCE FRMR/CMDR condition? jnz qlksta ;yes, verify again & restart ; lxi h,lkstat ;point to link status bit 3,m ;DCE busy? jnz txack ;yes, don't transmit I frame ; lxi h,l2stat ;point to level 2 status res 6,m ;else reset restransmission flag jmp txi2 ;and retransmit I frame ; ; not in timer recovery condition txi1: bit 2,m ;DCE FRMR/CMDR condition? rnz ;yes, don't transmit I frames ; bit 0,m ;link query in process? rnz ;yes, dont transmit yet ; lxi h,lkstat ;point to link status bit 3,m ;DCE busy? jnz txack ;yes, don't transmit I frame ; ; did we transmit new frame already? lda lastvs ;get last transmitted V(s) mov b,a ;save in lda vs ;get present vs cmp b ;same? jz txack ;yes, don't transmit I frame ; ; else set up retry counter for new frame mvi a,n2 ;else initialize retry count sta rtryct ; / lxi h,pfbit ;and set p=0 res 4,m ; / ; ; check that V(s) is within window txi2: lda lastnr ;get last valid N(r) adi kconst+1 ;calculate just past top of window ani 7 ;mod 7 mov e,a ;save in <e> lda vs ;get V(s) cmp e ;is V(s) past top of window? jz txack ;yes, don't transmit it yet ; ; is tx buffer ready? txi2a lxi h,txbtab ;point to tx bcb table lda vs ;get V(s) call bpoint ;get address of bcb call getrdy ;is buffer ready to tx? jz txack ;no, some other time ; ; transmit frame if not empty and ready shld txbcbp ;make buffer active call savbcb ;and save bcb pointers lda txcaddr ;<d>=outgoing command address mov d,a ; / ; lda vs ;get V(s) sta lastvs ;update last tx V(s) ; if debug ;if debug mode push psw ;save V(s) adi '0' ;convert to ASCII call ctype ;display it pop psw ;restore V(s) endif ;end of debug mode ; mvi b,ifid ;=I control byte rlc ;rotate V(s) into bits 1-3 ora b ;merge with control byte mov b,a ;save result in lda vr ;get V(r) (outgoing N(r)) sta lastvr ;update last tx V(r) mov c,a ;save in <c> call txframe ;transmit frame call t1on ;turn on timer T1 lhld txifct ;increment tx I frame count inx h ; / shld txifct ; / mvi a,kack ;reset acknowledgement delay counter sta ackcnt ; / ; ; timer recovery condition? lxi h,l2stat ;point to level 2 status bit 7,m ;timer recovery condition? rnz ;yes, don't update V(s) ; ; update V(s) to send next frame lda vs ;get V(s) mov b,a ;and save in inr a ;V(s)=V(s)+1 mod 7 ani 7 ; / sta vs ;update V(s) for next frame ; ; update max V(s) for acknowledge routine lda maxvs ;get current max V(s) txi4: cmp b ;is max V(s)= last tx V(s) jz txi5 ;yes, exit ; cmp e ;past top of window? rz ;yes, maxvs was max ; inr a ;else bump max V(s) mod(7) ani 7 ; / jmp txi4 ;and keep looping ; txi5: sta maxvs ;update max V(s) ret ;and exit ; ; transmit acknowledgement instead of I frame txack: lda lastvr ;get last transmitted V(r) mov b,a ;save in lda vr ;get V(r) cmp b ;same? rz ;yes, nothing to acknowledge ; ; wait a few tries to see if any I frames are coming lda ackcnt ;get delay count dcr a ;decrement count sta ackcnt ;and update count rnz ;wait a little longer until 0 ; ; delay count is 0, transmit acknowledge frame mvi a,kack ;reset delay count sta ackcnt ; / lxi h,lkstat ;else point to link status bit 4,m ;DTE busy? jnz txrnrr ;yes, transmit RNR frame ; jmp txrrr ;else transmit RR frame ; process timer T1 timeout condition ; (internally called) ; on entry: no parameters ; on exit: all regs, flags clobbered t1to: call t1off ;stop timer T1 lxi h,rtryct ;get retry count dcr m ;last retry? jz t1to9 ;yes, other end is dead ; lxi h,lkstat ;point to link status bit 0,m ;link connect in process? jz t1to1 ;no, keep going ; ; link connect is in process call ilprt ;print countdown db tab,'SABM tries to go =',0 lda rtryct ;print countdown mov l,a ; / mvi h,0 ; / call pdec ; / call ilprt ; / db cr,lf,0 ; / jmp txsabm ;and transmit SABM ; t1to1: bit 1,m ;disconnect in process? jz t1to2 ;no, keep going ; ; link disconnect is in process call ilprt ;print countdown db tab,'DISC tries to go =',0 lda rtryct ;print countdown mov l,a ; / mvi h,0 ; / call pdec ; / call ilprt ; / db cr,lf,0 ; / jmp txdisc ;and transmit DISC ; t1to2: lxi h,l2stat ;point to level 2 status bit 0,m ;link query in process jz t1to3 ;no, keep going ; ; link query is in process call ilprt ;print countdown db tab,'query tries to go =',0 lda rtryct ;print countdown mov l,a ; / mvi h,0 ; / call pdec ; / call ilprt ; / db cr,lf,0 ; / jmp qdce ;and query dce ; ; check that link is connected t1to3: lxi h,lkstat ;point to link status flags bit 2,m ;link connected? rz ;no, just return ; information flow is in process ; timeout recovery (x.25 para 2.4.6.8) lxi h,l2stat ;point to level 2 status setb 7,m ;indicate timer recovery condition setb 6,m ;set flag for retransmission call ilprt ;tell what we're doing db cr,lf,'L2: T1 timed out - ' db 'retransmitting I frame',0 lda lastnr ;make V(s)=last received N(r) sta vs ; / mov l,a ;print V(s) mvi h,0 ; / call pdec ; / call ilprt ;and try number db ' - tries to go =',0 lda rtryct ; / mov l,a ; / mvi h,0 ; / call pdec ; / call ilprt ;terminate line db cr,lf,0 ; / lxi h,pfbit ;set p=1 setb 4,m ; / lhld txirct ;increment retransmission log inx h ; / shld txirct ; / ret ; ; retry count exhausted t1to9: call ilprt db 'L2: tx retry count exhausted - ' db 'no reply from DCE',cr,lf,0 lxi h,lkstat ;point to link status bit 1,m ;was disconnect in process? jz t1to10 ;no, keep going ; ; disconnect was already in process res 1,m ;clear disconnect in process res 2,m ;and clear link connect flag ; t1to10: bit 2,m ;link connected? rz ;no, return ; ; link was connected (?) call ilprt db 'L2; disconnecting link',cr,lf,0 jmp disclk ;and disconnect ; transmit SABM command frame ; (internally called) ; on entry: no paramters ; on exit: all flags, regs clobbered txsabm: lxi h,lkstat ;point to link status setb 0,m ;signal connect in process lda txcaddr ;<d>=outgoing command address mov d,a ; / mvi b,sabmfid ;=SABM control byte mvi c,0 ;SABM is unnumbered call txframe ;transmit frame call t1on ;and turn on timer T1 ret ; transmit DISC command frame ; on entry: no paramters ; on exit: all flags, regs clobbered txdisc: lda txcaddr ;<d>=outgoing command address mov d,a ; / mvi b,discfid ;=DISC control byte mvi c,0 ;DISC is unnumbered call txframe ;transmit frame call t1on ;and turn on timer T1 ret ; transmit bad command frame ; on entry: no paramters ; on exit: all flags, regs clobbered txbadf: lda txcaddr ;<d>=outgoing command address mov d,a ; / mvi b,badfid ;=bad control byte mvi c,0 ;make it unnumbered call txframe ;transmit frame ret ; transmit RR command frame ; on entry: no paramters ; on exit: all flags, regs clobbered txrrc: lda txcaddr ;<d>=outgoing command address mov d,a ; / mvi b,rrfid ;=RR control byte lda vr ;get V(r) sta lastvr ;update last tx V(r) mov c,a ;save in <c> call txframe ;transmit frame call t1on ;turn on timer T1 ret ; transmit RNR command frame ; on entry: no paramters ; on exit: all flags, regs clobbered txrnrc: lda txcaddr ;<d>=outgoing command address mov d,a ; / mvi b,rnrfid ;=RNR control byte lda vr ;get V(r) sta lastvr ;update last tx V(r) mov c,a ;save in <c> call txframe ;transmit frame call t1on ;and turn on timer T1 ret ; transmit REJ command frame ; on entry: no paramters ; on exit: all flags, regs clobbered txrejc: lda txcaddr ;<d>=outgoing command address mov d,a ; / mvi b,rejfid ;=REJ control byte lda vr ;get V(r) sta lastvr ;update last tx V(r) mov c,a ;save in <c> call txframe ;transmit frame call t1on ;and turn on timer T1 ret ; *** outgoing responses *** ; transmit RR response frame ; on entry: no paramters ; on exit: all flags, regs clobbered txrrr: lda txraddr ;<d>=outgoing response address mov d,a ; / mvi b,rrfid ;=RR control byte lda vr ;get V(r) sta lastvr ;update last tx V(r) mov c,a ;save in <c> call txframe ;transmit frame ret ; transmit RNR response frame ; on entry: no paramters ; on exit: all flags, regs clobbered txrnrr: lda txraddr ;<d>=outgoing response address mov d,a ; / mvi b,rnrfid ;=RNR control byte lda vr ;get V(r) sta lastvr ;update last tx V(r) mov c,a ;save in <c> call txframe ;transmit frame ret ; transmit REJ response frame ; on entry: no paramters ; on exit: all flags, regs clobbered txrejr: lda txraddr ;<d>=outgoing response address mov d,a ; / mvi b,rejfid ;=REJ control byte lda vr ;get V(r) sta lastvr ;update last tx V(r) mov c,a ;save in <c> call txframe ;transmit frame ret ; transmit DM response frame ; on entry: no paramters ; on exit: all flags, regs clobbered txdm: lda txraddr ;<d>=outgoing response address mov d,a ; / mvi b,dmfid ;get DM control byte mvi c,0 ;DM is unnumbered call txframe ;transmit frame ret ; transmit UA response frame ; on entry: no paramters ; on exit: all flags, regs clobbered txua: lda txraddr ;<d>=outgoing response address mov d,a ; / mvi b,uafid ;get UA control byte mvi c,0 ;UA is unnumbered call txframe ;transmit frame ret ; transmit CMDR/FRMR response frame ; on entry: no paramters ; on exit: all flags, regs clobbered txfrmr: txcmdr: lxi h,txstat ;point to link SIO status bit 0,m ;tx busy? jnz txcmdr ;yes, wait ; lxi h,l2stat ;point to flow status word setb 1,m ;set DTE FRMR condition flag lxi h,txubcb ;point to CMDR frame buffer shld txbcbp ;and make buffer active lda cmdrf1 ;get rejected cmd control byte call putbuf ;put in buffer lda vs ;get V(s) rlc ;rotate into bits 1-3 mov b,a ;save in lda vr ;get V(r) rlc ;rotate into bits 5-7 rlc ; / rlc ; / rlc ; / rlc ; / ora b ;merge with V(s) call putbuf ;put in buffer lda cmdrf3 ;get error indicator byte call putbuf ;put in buffer lda txraddr ;<d>=outgoing response address mov d,a ; / mvi b,cmdrfid ;=CMDR control byte mvi c,0 ;CMDR is unnumbered call txframe ;transmit frame ret ; *** common routines *** ; transmit frame ; (internally called) ; on entry: =frame control byte ; <c>=0 if unnumbered, N(r) otherwise ; <d>=frame address byte ; pfbit=poll/final bit in pos 4 ; on exit: flags, registers clobbered ; txaddr= address byte ; txctrl= control byte txframe: lhld txfct ;increment tx frame counter inx h ; / shld txfct ; / lxi h,txstat ;point to SIO status txf1: bit 0,m ;tx busy? jnz txf1 ;yes, wait ; mov a,d ;get address byte sta txaddr ;store address mov a,c ;get N(r) rlc ;rotate into bits 5-7 rlc ; / rlc ; / rlc ; / rlc ; / ora b ;merge with control byte mov b,a ;save result in lda pfbit ;get poll/final bit ora b ;merge it into control byte sta txctrl ;store control byte call logtx ;log transmission xra a ;clear p/f bit for next frame sta pfbit ; / call txwake ;start transmission and T1 timer ret ; log transmitted frame ; (internally called) ; on entry: txaddr= address byte ; txctrl= control byte ; on exit: <a>, flags clobbered ; all other regs unchanged logtx: push h ;save <hl> lxi h,fstat ;point to file status bit 7,m ;log file open? pop h ;restore <hl> rz ;no, return with no action ; mvi a,1 ;else signal tx frame call logdat ;put in file lda txaddr ;get address call logdat ;put in file lda txctrl ;get control call logdat ;put in file xra a ;and put zeros in rest of block call logdat ; / call logdat ; / call logdat ; / call logdat ; / call logdat ; / call logdat ; / call logdat ; / call logdat ; / call logdat ; / call logdat ; / call logdat ; / call logdat ; / call logdat ; / ret ; ************************* ; * receive section * ; ************************* ; process a received frame if available ; (internally and externally called) ; on entry: no parameters ; on exit: <c>=buffer # if available ; <hl>=bcb address if available ; <d>=address byte rxfrm: lxi h,rxflst ;point to list of rx frames call getbuf ;any waiting? rc ;no, return ; mov c,a ;save buffer # in <c> lxi h,rxbtab ;point to table of buffer addresses call bpoint ;get address of bcb call dcrbuf ;discard CRC-1 byte call getbuf ;get address byte jnc rxfrm0 ;keep going if there ; ; empty frame mov a,c ;else release rx buffer call rlsrxb ; / call ilprt ;and tell operator db 'L2: rx empty frame (no control byte)',cr,lf,0 ret ; rxfrm0: mov d,a ;save in <d> lda rxcaddr ;incoming command? cmp d ; / jz incmd ;yes, process it ; lda rxraddr ;incoming response? cmp d ; / jz inresp ;yes, process it ; ; process bad address call ilprt db cr,lf,'L2: bad rx address: ',0 mov a,d ;get bad address byte call phex ;print address in hex ; ;*** dump entire frame in hex for debug if debug call ilprt db cr,lf,'L2: frame contents: ',0 rxfrlp: call getbuf ;get next octet jc rxfrm1 ;exit if no more call phex ;print it in hex mvi a,' ' ;and a separator call ctype ; / jmp rxfrlp ;and go back for more endif ;end of debug option ; rxfrm1: call ilprt ;terminate error msg line db cr,lf,0 ; / mov a,c ;get rx buffer # call rlsrxb ;and release it lhld rbafct ;increment bad address counter inx h ; / shld rbafct ; / ret ; process incoming comand frame ; (internally called) ; on entry: <hl>=bcb address ; <c>= rx buffer # ; <d>=address byte ; on exit: =control byte ; <c>,<d>,<hl> unchanged incmd: call getbuf ;get control byte jnc incmd1 ;if there is one ; mov a,c ;else release rx buffer call rlsrxb ; / lhld rxbcct ;increment bad command count inx h ; / shld rxbcct ; / ret ; incmd1: mov b,a ;save control byte in sta cmdrf1 ;save it in case of CMDR ani 0001$0000b ;extract P bit sta pfbit ;set F bit for reply push h ;save <hl> lhld rxcfct ;increment rx command count inx h ; / shld rxcfct ; / call logrx ;log received frame lxi h,lkstat ;point to link status word bit 2,m ;link disconnected? pop h ;restore <hl> jz dphase ;yes, process disconnected phase ; ; link is connected ; branch to know frame id's mov a,b ;get control byte bit 0,a ;I frame? jz rxi ;yes, process it ; ani 1110$1111b ;extract all bits except p/f cpi sabmfid ;SABM frame? jz rxsabm ;yes, process it ; cpi discfid ;DISC frame? jz rxdisc ;yes, process it ; ; branch to numbered frames ani 0000$1111b ;discard N(r) sequence bits cpi rrfid ;RR command frame? jz rxcrr ;yes, process it ; cpi rnrfid ;RNR command frame? jz rxcrnr ;yes, process it ; cpi rejfid ;REJ command frame? jz rxcrej ;yes, process it ; ; unrecognized frame identifier mov a,c ;else get buffer # call rlsrxb ;discard unknown rx frame lhld rxbcct ;increment bad cmd counter inx h ; / shld rxbcct ; / lxi h,cmdrf2 ;clear CMDR bit 13 for cmd res 4,m ; / lxi h,cmdrf3 ;set CMDR bit W setb 0,m ; / res 1,m ;and reset bit X res 2,m ;and bit Y res 3,m ;and bit Z jmp txcmdr ;and transmit CMDR ; ; process link disconnected phase dphase: mov a,c ;get rx buffer # call rlsrxb ;and release buffer mov a,b ;get control byte ani 1110$1111b ;strip p bit cpi sabmfid ;SABM frame? jz rxsabm ;yes, process it ; ; reply DM to any other command frames with P=1 bit 4,b ;P=1? rz ;no, exit ; jmp txdm ;yes, send DM response ; log incoming frame ; (internally called) ; on entry: =control byte ; <d>=address byte ; on exit: <a>,flags clobbered ; all other regs unchanged logrx: push h ;save <hl> lxi h,fstat ;point to file status bit 7,m ;log file open? pop h ;restore <hl> rz ;no, do nothing ; mvi a,0 ;else signal rx frame call logdat ;and put in file mov a,d ;get address call logdat ;and put in file mov a,b ;get control byte call logdat ;and put in file xra a ;put zeroes in rest of block call logdat ; / call logdat ; / call logdat ; / call logdat ; / call logdat ; / call logdat ; / call logdat ; / call logdat ; / call logdat ; / call logdat ; / call logdat ; / call logdat ; / call logdat ; / ret ; process received SABM command frame ; (internally called) ; on entry: <hl>=bcb address ; =control byte ; <c>=rx buffer # rxsabm: call getbuf ;check if any I bits jnc cfmterr ;yes, format error ; mov a,c ;get rx buffer # call rlsrxb ;release buffer call t1off ;turn off timer T1 call reset ;clear flow control variables lxi h,lkstat ;point to link status setb 2,m ;set link active flag call ilprt ;tell operator link is ok db 'L2: rx SABM - link connected by dce',cr,lf,0 jmp txua ;and transmit UA ; process received DISC command frame ; (internally called) ; on entry: <hl>=bcb address ; =control byte ; <c>=rx buffer # rxdisc: call getbuf ;check if any I bits jnc cfmterr ;yes, format error ; mov a,c ;release rx buffer call rlsrxb ; / call t1off ;turn off timer T1 lxi h,lkstat ;point to link status mvi m,0 ;clear everything setb 2,m ;except link connected setb 1,m ;and link disc in process call ilprt ;tell operator link is down db 'L2: rx DISC - link disconnected by dce',cr,lf,0 call txua ;transmit UA lxi h,lkstat ;point to link status res 1,m ;clear disc in process res 2,m ;and link connected ret ; process received RR command frame ; (internally called) ; on entry: <hl>=bcb address ; =control byte ; <c>=rx buffer # rxcrr: call ackdge ;acknowledge pending frames jc badnr ;exit if invalid N(r) ; call getbuf ;another byte in buffer? jnc cfmterr ;yes, format errer ; lxi h,lkstat ;point to link status byte res 3,m ;clear DCE busy res 7,m ;clear DCE reject condition jmp rxsc ;and process supervisory cmd ; process received RNR command frame ; (internally called) ; on entry: <hl>=bcb address ; =control byte ; <c>=rx buffer # rxcrnr: call ackdge ;acknowledge pending frames jc badnr ;exit if invalid N(r) ; call getbuf ;another byte in buffer? jnc cfmterr ;yes, format errer ; mvi a,n2 ;reset tx retry counter sta rtryct ; / lxi h,lkstat ;point to link status byte setb 3,m ;set DCE busy res 7,m ;clear DCE reject condition jmp rxsc ;and process supervisory cmd ; process received REJ command frame ; (internally called) ; on entry: <hl>=bcb address ; =control byte ; <c>=rx buffer # rxcrej: call ackdge ;acknowledge pending frames jc badnr ;exit if invalid N(r) ; call getbuf ;another byte in buffer? jnc cfmterr ;yes, format errer ; lxi h,lkstat ;point to link status byte res 3,m ;clear DCE busy setb 7,m ;set DCE reject condition flag mvi a,n2 ;initialize retry counter sta rtryct ; / mov a,b ;get control byte call getnr ;extract valid N(r) sta vs ;set V(s)=N(r) for retransmission sta maxvs ;and update max V(s) for acknowledge ; rxsc: ;process supervisory cmd mov a,c ;release rx buffer call rlsrxb ; / bit 4,b ;P=1? rz ;no, do nothing here ; lxi h,lkstat ;point to link status word bit 4,m ;DTE busy? jz txrrr ;no, transmit RR response jmp txrnrr ;yes, transmit RNR response ; handle invalid received N(r) ; on entry: <c>=rx buffer # badnr: mov a,c ;get rx buffer # call rlsrxb ;release it ;*** below message added for diagnostic call ilprt db 'L2: bad received N(r)',cr,lf,0 ; set up FRMR information fields lxi h,cmdrf3 ;point to CMDR field 3 res 0,m ;reset bits W, X and Y res 1,m ; / res 2,m ; / setb 3,m ;set bit Z for invalid N(r) jmp txfrmr ;and transmit FRMR ; handle received frame format error ; (I field in a non I frame) ; (internally called) ; on entry: <hl>=bcb address ; <c>=buffer # cfmterr: ;error in command frame lxi h,cmdrf2 ;point to CMDR field 2 res 4,m ;reset bit 4 for commands jmp fmterr ;and continue ; rfmterr: ;error in response frame lxi h,cmdrf2 ;point to CMDR field 2 setb 4,m ;set bit 4 for responses fmterr: mov a,c ;get rx buffer # call rlsrxb ;release buffer lxi h,cmdrf3 ;point to CMDR field 3 setb 0,m ;set bit W setb 1,m ;and bit X res 2,m ;reset bit Y res 3,m ;and bit Z jmp txcmdr ;and transmit CMDR ; process received I frame ; (internally called) ; on entry: <hl>=bcb address ; =control byte ; <c>=rx buffer # ; on exit: flags, regs clobbered rxi: call ackdge ;acknowledge tx frame jc badnr ;exit if invalid N(r) ; rxi1: push h ;save bcb address lxi h,lkstat ;point to link status res 7,m ;clear DCE REJ condition pop h ;restore bcb address mov a,b ;get control byte ani 0000$1110b ;extract N(s) rrc ;move to bits 0-2 mov b,a ;and save in lda vr ;get V(r) cmp b ;is N(s)=V(r)? jz rxi2 ;yes, keep going ; ; process invalid received N(s) mov a,c ;else get rx buffer # call rlsrxb ;release buffer lxi h,lkstat ;point to link status setb 6,m ;set REJ condition jmp txrejr ;and transmit REJ response ; ; process valid N(s) (update receive window ; and hand over packet to level 3) rxi2: inr a ;V(r)=V(r)+1 mod 7 ani 7 ; / sta vr ;update V(r) push h ;save bcb address lxi h,lkstat ;point to link status res 6,m ;clear DTE REJ condition pop h ;restore bcb address call getbct ;empty frame? jnz rxi3 ;no, keep going ; ; empty frame mov a,c ;release rx buffer call rlsrxb ; / call ilprt ;and tell operator db 'L3: rx empty I frame',cr,lf,0 ret ; ; frame is not empty rxi3: lxi h,rxplst ;point to list of rx packets mov a,c ;get buffer # call putbuf ;hand over buffer lhld rxifct ;update rx I frame counter inx h ; / shld rxifct ; / ret ; process received N(r) to acknowledge tx I frames ; (internally called) ; on entry: =control byte with N(r) ; <c>=buffer # ; on exit: carry set if invalid N(r) ; <a>, other flags clobbered ; all other regs unchanged ackdge: push b ;save regs push d ; / push h ; / mov a,b ;get control byte call getnr ;extract N(r) mov d,a ;save N(r) in <d> lda lastnr ;get last rx N(r) cmp d ;same as this one? jz ackexi ;yes, nothing new ; ; calculate top of receive window lda maxvs ;max V(s)+1 mod (7) inr a ;(=top edge of window) inr a ;bump just past top ani 7 ; / mov e,a ; / ; check for valid N(r) mvi b,kconst+1 ;=k+1 lda lastnr ;<a>=last valid N(r) ack1: cmp d ;<a>=N(r)? jz ack2 ;yes, valid N(r) ; inr a ;bump <a> mod 7 ani 7 ; / cmp e ;<a>=past top of window? jz ackerr ;yes, invalid N(r) ; dcr b ;decrement window count jz ackerr ;error, below lower edge ; jmp ack1 ;else keep looping ; ; valid N(r), acknowledge all tx frames up to N(r)-1 ack2: call t1off ;stop timer T1 lxi h,txbtab ;point to tx bcb address table acklp: lda lastnr ;get last valid N(r) cmp d ;is N(r)=last valid N(r)? jz allack ;yes, all acknowledged ; ; acknowledge a new frame dcr a ;calculate last N(r)-1 ani 7 ;mod 7 call bpoint ;point to bcb address of last N(r)-1 call clrbuf ;clear tx buffer for new use lda lastnr ;get last valid N(r) inr a ;bump last valid N(r) ani 7 ; / sta lastnr ; / mvi a,n2 ;reset tx retry counter sta rtryct ; / jmp acklp ;and keep looping ; ; no more frames to acknowledge this time allack: lda maxvs ;is N(r)=max V(s)+1? inr a ; / ani 7 ; / cmp d ; / cnz t1on ;no, some frames still outstanding stc ;reset carry flag cmc ; / jmp ackexi ;and exit ; ; signal invalid N(r) ackerr: stc ;set carry flag ; ; common exit routine ackexi: pop h ;restore regs pop d ; / pop b ; / ret ; extract N(r) from control byte ; (internally called) ; on entry: <a>=control byte ; on exit: <a>=N(r) getnr: ani 1110$0000b ;extract N(r) rrc ;move to bits 0-2 rrc ; / rrc ; / rrc ; / rrc ; / ret ; process incoming response frame ; (internally called) ; on entry: <hl>=bcb address ; <c>=rx buffer # ; <d>=address byte ; on exit: =control byte ; <c>,<d>,<hl> unchanged inresp: call getbuf ;get control byte jnc inrsp1 ;if there is one ; mov a,c ;else release rx buffer call rlsrxb ; / lhld rxbrct ;incr bad response frame count inx h ; / shld rxbrct ; / ret ; inrsp1: mov b,a ;save control byte sta cmdrf1 ;save it in case of FRMR push h ;save <hl> lhld rxrfct ;increment response count inx h ; / shld rxrfct ; / call logrx ;log received frame pop h ;restore <hl> mov a,b ;get control byte ani 1110$1111b ;extract all bits except f ; now branch to known frame id's cpi dmfid ;DM frame? jz rxdm ;yes, process it ; cpi uafid ;UA frame? jz rxua ;yes, process it ; cpi cmdrfid ;CMDR/FRMR frame? jz rxcmdr ;yes, process it ; ; branch to numbered frames ani 0000$1111b ;discard N(r) sequence bits cpi rrfid ;RR response frame? jz rxrrr ;yes, process it ; cpi rnrfid ;RNR response frame? jz rxrrnr ;yes, process it ; cpi rejfid ;REJ response frame? jz rxrrej ;yes, process it ; ; unknown frame id badrsp: mov a,c ;else get rx buffer # call rlsrxb ;and release buffer lhld rxbrct ;increment bad response counter inx h ; / shld rxbrct ; / lxi h,cmdrf2 ;set FRMR bit 13 setb 4,m ; / lxi h,cmdrf3 ;and FRMR bit W setb 0,m ; / res 1,m ;reset FRMR bits X,Y,Z res 2,m ; / res 3,m ; / jmp txfrmr ;and transmit FRMR ; process received RR response frame ; (internally called) ; on entry: <hl>=bcb address ; =control byte ; <c>=rx buffer # rxrrr: call ackdge ;acknowledge pending frames jc badnr ;process invalid N(r) ; call getbuf ;another byte in buffer? jnc rfmterr ;yes, format errer ; lxi h,lkstat ;point to link status byte res 3,m ;clear DCE busy res 7,m ;clear DCE reject condition lxi h,l2stat ;point to level 2 status bit 0,m ;link query in process? jz rxsr ;no, do common stuff ; ; link query is in process bit 4,b ;is response F=1? jz rxsr ;no, do common stuff ; ; process reply to query res 0,m ;reset link query flag call t1off ;turn off response timer call ilprt db 'L2: dce ready',cr,lf,0 jmp rxsr ;and do common stuff ; process received RNR response frame ; (internally called) ; on entry: <hl>=bcb address ; =control byte ; <c>=rx buffer # rxrrnr: call ackdge ;acknowledge pending frames jc badnr ;process invalid N(r) ; call getbuf ;another byte in buffer? jnc rfmterr ;yes, format errer ; mvi a,n2 ;reset tx retry counter sta rtryct ; / lxi h,lkstat ;point to link status byte setb 3,m ;set DCE busy res 7,m ;clear DCE reject condition lxi h,l2stat ;point to level 2 status bit 0,m ;link query in process? jz rxsr ;no, do common stuff ; ; link query is in process bit 4,b ;is response F=1? jz rxsr ;no, do common stuff ; ; process reply to query res 0,m ;reset link query flag call t1off ;turn off response timer call ilprt db 'L2: dce busy',cr,lf,0 jmp rxsr ;and do common stuff ; process received REJ response frame ; (internally called) ; on entry: <hl>=bcb address ; =control byte ; <c>=rx buffer # rxrrej: call ackdge ;acknowledge pending frames jc badnr ;process invalid N(r) ; call getbuf ;another byte in buffer? jnc rfmterr ;yes, format errer ; lxi h,lkstat ;point to link status byte res 3,m ;clear DCE busy setb 7,m ;set DCE reject condition flag mvi a,n2 ;initialize retry counter sta rtryct ; / mov a,b ;get control byte call getnr ;extract valid N(r) sta vs ;set V(s)=N(r) for retransmission sta maxvs ;and update max V(s) for acknowledge lxi h,l2stat ;point to level 2 status bit 0,m ;link query in process? jz rxsr ;no, do common stuff ; ; link query is in process bit 4,b ;is response F=1? jz rxsr ;no, do common stuff ; ; process reply to query res 0,m ;reset link query flag call t1off ;turn off response timer call ilprt db 'L2: dce in REJ condition',cr,lf,0 jmp rxsr ;and do common stuff ; ; common stuff for supervisory response frames rxsr: mov a,c ;release rx buffer call rlsrxb ; / lxi h,l2stat ;point to level 2 status flags bit 7,m ;timer recovery condition? rz ;no, exit ; ; process timer recovery condition bit 4,b ;is F=1? rz ;no, exit ; res 7,m ;else clear timer recovery condition ret ; process received DM response frame ; (internally called) ; on entry: <hl>=bcb address ; =control byte ; <c>=rx buffer # rxdm: call getbuf ;get next byte jnc rfmterr ;process invalid format ; mov a,c ;get rx buffer # call rlsrxb ;release buffer lxi h,lkstat ;link connect in process? bit 0,m ; / jz rxdm1 ;no, keep going ; call ilprt ;yes, tell operator db 'L2: rx DM - dce unable to connect',cr,lf,0 ret ; rxdm1: setb 0,m ;set link conn in process res 2,m ;clear link connected jmp txsabm ;and transmit SABM ; process received UA response frame ; (internally called) ; on entry: <hl>=bcb address ; =control byte ; <c>=rx buffer # rxua: call getbuf ;get next byte jnc rfmterr ;process invalid format ; mov a,c ;release rx buffer call rlsrxb ; / lxi h,lkstat ;point to link status word res 3,m ;clear DCE busy bit 0,m ;connect in process? jz rxua1 ;no, keep going ; res 0,m ;else clear connect in process setb 2,m ;and set connect flag call ilprt ;and tell operator db 'L2: rx UA - link connected',cr,lf,0 call t1off ;turn off timer T1 call txstar ;transmit level 3 restart packet ret ; rxua1: bit 1,m ;disconnect in process? rz ;no, do nothing ; res 1,m ;else clear disc in process res 2,m ;and clear connect flag call ilprt ;and tell operator db 'L2: rx UA - link disconnected',cr,lf,0 call t1off ;turn off timer T1 ret ; process received CMDR/FRMR response frame ; (internally called) ; on entry: <hl>=bcb address ; <c>=rx buffer # rxcmdr: call ilprt ;display error msg db cr,lf,'L2: rx CMDR/FRMR - frame rejected: ',cr,lf,0 call getbuf ;get next byte jc rcmdr3 ;error if not there ; mov b,a ;save byte in call ilprt ;print first I field db tab,'rejected frame id = ',0 mov a,b ;get back byte call phex ;else display first byte in hex call ilprt ;and terminate line db cr,lf,0 ; / ; call getbuf ;get second error byte jc rcmdr3 ;error if not there ; mov b,a ;save byte in call ilprt ;display second field parameters db tab,'rej frame type = ',0 bit 4,b ;command frame? jz rcmdr1 ;yes, say so ; call ilprt ;else was response db 'response',cr,lf,0 jmp rcmdr2 ; rcmdr1: call ilprt ;command frame db 'command',cr,lf,0 ; rcmdr2: call ilprt ;display other field paramters db tab,' dce V(s) = ',0 push h ;save <hl> mov a,b ;get back byte ani 0000$1110b ;extract V(s) rrc ; / mvi h,0 ;print V(s) mov l,a ; / call pdec ; / call ilprt ;terminate line db cr,lf db tab,' dce V(r) = ',0 mov a,b ;get back byte call getnr ;extract V(r) mov l,a ;and print it call pdec ; / call ilprt ;teminate line db cr,lf,0 pop h ;restore <hl> ; call getbuf ;get last byte jc rcmdr3 ;error if not there ; mov b,a ;save byte in call ilprt ;else print last field db tab,'error bits ----zyxw=',0 mov a,b ;get back byte call pbin ;in binary call ilprt ;and terminate line db cr,lf,0 ; / ; call getbuf ;try for one more jc rcmdr4 ;ok if not there ; rcmdr3: call ilprt db 'L2: format error in rx CMDR/FRMR frame',cr,lf,0 ; rcmdr4: mov a,c ;else release rx buffer call rlsrxb ; / ; lxi h,l2stat ;point to flow status setb 2,m ;set DCE FRMR condition jmp conlk ;and reconnect link ; ***************** ; * data area * ; ***************** dseg ; HDLC frame variables and sequence numbers vr db 0 ;V(r)=receive state variable (0-7) vs db 0 ;V(s)=send state variable (0-7) lastnr db 7 ;last valid received N(r) (0-7) lastvr db 0 ;last transmitted V(r) lastvs db 7 ;last transmitted V(s) maxvs db 0 ;max V(s) transmitted pfbit db 0 ;poll/final bit (in pos 4) rxcaddr db 0 ;address of received commands rxraddr db 0 ;address of received responses txcaddr db 0 ;address of transmitted commands txraddr db 0 ;address of transmitted responses ; outgoing CMDR information field template ; (table 4/X.25) cmdrf1 db 0 ;rejected command control field cmdrf2 db 0 ;sequence variables & addr indicator cmdrf3 db 0 ;error indicator bits ; level 2 status indicators & local variables lkstat db 0 ;level 2 link status flags l2stat db 0 ;level 2 status flags dtemod db true ;0=DCE mode/0ffh=DTE mode badadd db 0 ;storage for bad address ackcnt db kack ;acknowledgement delay counter ; level 2 diagnostic counters rtryct: db n2 ;tx retry counter rbafct: dw 0000h ;bad rx address frames rxbrct: dw 0000h ;bad rx response frames rxbcct: dw 0000h ;bad rx command frames rxcfct: dw 0000h ;rx command frames rxrfct: dw 0000h ;rx response frames rxifct: dw 0000h ;rx I frames txifct: dw 0000h ;tx I frames txfct: dw 0000h ;tx frames txirct: dw 0000h ;tx I retransmission count