****************************************************************************** * * THIS SOURCE CODE IS FREE SOFTWARE; YOU CAN REDISTRIBUTE IT * AND/OR MODIFY IT WITHOUT RESTRICTION. * * THIS SOURCE CODE 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. * * CREDITS: * THE INSPIRATION FOR THESE ROUTINES CAME FROM THE COMM6 * PROGRAM BY BILL YAKOWENKO. THE COMM6 SOURCE CODE WAS * LAST KNOWN TO RESIDE HERE: * * * * REVISION HISTORY: * APR-30-2007 - REVISED TIMING DATA TO REFLECT THE ACTUAL * 0.89488625 MHz FREQUENCY USED IN THE COCO. * - MINOR CHANGES TO THE CODE FLOW IN THE TRANSMITTER. * - THE TRANSMITTER NO LONGER PRESERVES THE Y REGISTER. * * APR-27-2007 - ADDED SETDP DIRECTIVES TO PREVENT ASSEMBLER BARFING. * * APR-26-2007 - INITIAL PUBLIC RELEASE. * *----------------------------------------------------------------------------- * * THE SUBROUTINES IN THIS FILE PROVIDE GENERAL PURPOSE SERIAL I/O THROUGH * THE TRS-80 COLOR COMPUTER'S BIT-BANGER PORT AT 57600 / 115.2K BAUD. * * ON A COCO 1 OR 2 THESE ROUTINES ONLY SUPPORT 57600 BAUD RUNNING AT * THE STANDARD 0.89 MHZ SPEED. WHEN RUN ON A COCO 3, THE ROUTINES * OPERATE AT EITHER 57600 OR 115.2K BAUD BY SETTING THE CPU RATE TO * 0.89 MHZ OR 1.78 MHZ RESPECTIVELY. * * DUE TO THE TIMING CRITICAL NATURE OF THIS CODE, IT IS ESSENTIAL THAT * ANY ASSEMBLER USED TO BUILD IT WILL PRODUCE THE EXPECTED OBJECT CODE. * IN PARTICULAR, THE '<' CHARACTER IS USED TO PREFIX OPERANDS THAT * REQUIRE DIRECT ADDRESSING, AND INDEXED OPERANDS WITH NO OFFSET MUST * USE A ZERO-OFFSET POST-BYTE. * * THE CODE SHOULD FUNCTION ON BOTH 6809 AND 6309 PROCESSORS, SO LONG AS * THE 6309 IS NOT RUNNING IN NATIVE MODE (REDUCED CYCLES). * * THE CODE IS COMPLETELY POSITION-INDEPENDENT, AND DOES NOT USE ANY ROM * ROUTINES OR SYSTEM VARIABLES. * ****************************************************************************** ORG $0000 ; POSITION-INDEPENDENT - CAN BE LOADED ANYWHERE ****************************************************************************** * COCO 57600 / 115.2K BAUD BIT-BANGER RECEIVE ****************************************************************************** * * THIS SUBROUTINE WILL WAIT FOR A SPECIFIED TIMEOUT PERIOD * UNTIL A START-BIT APPEARS ON THE BIT-BANGER INPUT. IF A * START-BIT IS DETECTED, THEN A LOOP IS EXECUTED TO READ * THE SERIAL DATA. THE DATA FORMAT MUST BE: * 1 START-BIT, 8 DATA BITS, NO PARITY, 1..2 STOP-BITS. * * THE RECEIVE LOOP TERMINATES WHEN: * - THE MAXIMUM NUMBER OF BYTES REQUESTED HAVE BEEN RECEIVED. * - A PERIOD OF APPROX 7.5 MS (3.25 MS) ELLAPSES WITHOUT A NEW START-BIT * - A FRAMING ERROR IS DETECTED. * * THE SUBROUTINE ALSO RETURNS A SIXTEEN-BIT CHECKSUM OF THE * DATA RECEIVED. THIS CHECKSUM IS CALCUALTED BY STARTING WITH * ZERO AND THEN ADDING IN THE UNSIGNED 8-BIT VALUE OF EACH * DATA BYTE AS IT IS RECEIVED. * * IF YOU PASS 0 IN EITHER THE REQUEST COUNT OR TIMEOUT PARAMETERS * THEN THE SUBROUTINE RETURNS WITHOUT DOING ANYTHING. * * ON ENTRY: * X = ADDRESS OF THE RECEIVE BUFFER * Y = REQUEST COUNT (MAXIMUM NUMBER OF BYTES TO RECEIVE) * D = TIMEOUT VALUE (133 = APPROX ONE SECOND @ 0.89 MHz) * * ON EXIT: * Y = DATA CHECKSUM * D = ACTUAL NUMBER OF BYTES RECEIVED * X AND U ARE PRESERVED * CC.CARRY IS SET IF A FRAMING ERROR WAS DETECTED * READBIT EQU $FF22 ; ADDRESS OF THE BIT-BANGER INPUT * LOCAL STACK VARIABLES (OFFSETS FROM S) TIMEOUT EQU 0 ; TIMEOUT COUNTER (VALUE IS CRITICAL FOR TIMING) BUFSTRT EQU 2 ; BUFFER START ADDRESS CHKSUM EQU 4 ; CHECKSUM VALUE LOCLSZ EQU 6 ; TOTAL SIZE OF LOCAL STACK VARIABLES RECV56K ANDCC #$FE ; CLEAR CARRY FLAG (NO FRAMING ERROR) PSHS CC,DP,X,U ; PRESERVE REGISTERS ORCC #$50 ; MASK INTERRUPTS LEAS -LOCLSZ,S ; ALLOCATE SPACE ON STACK FOR VARIABLES STD TIMEOUT,S ; SET TIMEOUT COUNTER VARIABLE STX BUFSTRT,S ; SAVE BUFFER START ADDRESS LEAU -1,X ; INITIALIZE READ PTR FOR PRE-INCREMENT LDA #$FF ; SETUP THE DP REGISTER TO.. TFR A,DP ; ..ACCESS THE I/O PAGE ($FFxx) LDB ,U ; GET NEGATIVE VALUE OF THE BYTE THAT.. NEGB ; ..PRECEDES THE BUFFER AND STORE IT.. STD CHKSUM,S ; ..AS THE INITIAL CHECKSUM VALUE. CMPY #0 ; CHECK THE REQUEST COUNT AND.. LBEQ RCVDONE ; ..EXIT IF NOTHING REQUESTED LDB #1 ; SET B TO THE BIT-BANGER INPUT MASK LEAX TIMEOUT+1,S ; POINT X TO LSB OF THE TIMEOUT COUNTER SETDP $FF ; INFORM ASSEMBLER OF NEW DP VALUE * INTERLEAVE START-BIT DETECTION WITH A DECREMENT OF THE TIMEOUT COUNTER LSB TOTICK BITB = 0 * INTERLEAVE START-BIT DETECTION WITH A DECREMENT OF THE TIMEOUT COUNTER MSB * * NOTE: THE "TIMEOUT" EQUATE IS NOT USED HERE BECAUSE SOME * ASSEMBLERS FAIL TO PRODUCE THE "ZERO-OFFSET" POST-BYTE * IF THERE IS *ANYTHING* PRECEDING THE COMMA. * BITB | * | | * |<-- 15.54 -->| | * | | | * * --------------------\ Start Bit /-------------\ * \-------------/ Data Bit 0 \-------- * * Detection window --> xxxxxxxxxxx xxxxxxxxxxx <-- Sampling window * | | | * |<-- 11 ->| | * | | * | | | * 5.5 --->| |<---- 17.81 --->| * * * THERE ARE ROUGHLY 15.54 CYCLES PER-BIT (894886.25 / 57600). DETECTION OF THE * START-BIT MAY HAVE OCCURED ANYWHERE WITHIN THE FIRST 11 CYCLES. IDEALLY, WE * WOULD LIKE THE SAMPLING POINT TO BE CENTERED WITHIN EACH DATA BIT. THERE ARE * ABOUT 17.81 CYCLES BETWEEN THE CENTER OF THE START-BIT DETECTION WINDOW AND * THE CENTER OF THE FIRST DATA BIT. THE CPU INSTRUCTIONS WHICH DETECTED THE * START-BIT AND BROUGHT US HERE (BITB/BEQ) USED 7 CYCLES, LEAVING ANOTHER * 10.81 CYCLES (11) TO CONSUME BEFORE SAMPLING THE FIRST DATA BIT. * * WE NEED TO CALCULATE THE OPTIMAL SAMPLING TIME FOR EACH SUBSEQUENT BIT AND * ROUND TO THE NEAREST CYCLE. STARTBT LDD #$0000 3 \ ; RESET THE TIMEOUT COUNTER.. STD ,S 5 | 11 ; ..FOR SUBSEQUENT BYTES ABX 3 / ; CONSUME 3 CYCLES ; WANTED 10.81 / USED 11 / 0.19 LATE * SAMPLE DATA BIT 0 LDB