- Fully Commented Commodore 64 KERNAL ROM Disassembly (English, "CBM") - - The comments have been taken from - The original C64 KERNAL source by Commodore (901227-03) - https://github.com/mist64/cbmsrc - https://www.pagetable.com/?p=894 - - The comments here are basically a complete copy of the original - source code, lined up with the version in the C64 ROM. - This way, even all variable names are intact. - - Converted and formatted by Michael Steil - - Corrections (formatting, lining up) welcome at: - https://github.com/mist64/c64disasm - ------------------------------------------------------------ - # This plain text file is formatted so that it can be automatically # parsed in order to create cross-references etc. # * Lines starting with "-" is top-level information. The first line # is the title. Lines starting with "--" are separators. # * Lines starting with "#" are internal comments. # * Lines starting with ".," indicate code to be disassembled. # * Lines starting with ".:" indicate bytes to be dumped. # * Comments start at the 33rd column. # * 32 leading spaces and ".LIB" indicate a heading. # * Otherwise, 32 leading spaces indicate an overflow comment. # The encoding is UTF-8. ; ; This code is a subset of the original c64 kernal code. ; It has been modified to implement the load and save IEC routines ; to be run on a KIM-1 single board computer. ; The code assumes a ROM expansion on the KIM-1 at $2000. ; ; Modified June, 2022 by Dave McMurtrie .LIB DISCLAIMER ;**************************************** ;* * ;* KK K EEEEE RRRR NN N AAA LL * ;* KK KK EE RR R NNN N AA A LL * ;* KKK EE RR R NNN N AA A LL * ;* KKK EEEE RRRR NNNNN AAAAA LL * ;* KK K EE RR R NN NN AA A LL * ;* KK KK EE RR R NN NN AA A LL * ;* KK KK EEEEE RR R NN NN AA A LLLLL * ;* * ;*************************************** ; ;*************************************** ;* PET KERNAL * ;* MEMORY AND I/O DEPENDENT ROUTINES * ;* DRIVING THE HARDWARE OF THE * ;* FOLLOWING CBM MODELS: * ;* COMMODORE 64 OR MODIFED VIC-40 * ;* COPYRIGHT (C) 1982 BY * ;* COMMODORE BUSINESS MACHINES (CBM) * ;*************************************** ;****LISTING DATE --1200 14 MAY 1982**** ;*************************************** ;* THIS SOFTWARE IS FURNISHED FOR USE * ;* USE IN THE VIC OR COMMODORE COMPUTER* ;* SERIES ONLY. * ;* * ;* COPIES THEREOF MAY NOT BE PROVIDED * ;* OR MADE AVAILABLE FOR USE ON ANY * ;* OTHER SYSTEM. * ;* * ;* THE INFORMATION IN THIS DOCUMENT IS * ;* SUBJECT TO CHANGE WITHOUT NOTICE. * ;* * ;* NO RESPONSIBILITY IS ASSUMED FOR * ;* RELIABILITY OF THIS SOFTWARE. RSR * ;* * ;*************************************** .END STATUS = $90 ;I/O OPERATION STATUS BYTE C3P0 = $94 ;IEEE BUFFERED CHAR FLAG BSOUR = $95 ;CHAR BUFFER FOR IEEE R2D2 = $A3 ;SERIAL BUS USAGE BSOUR1 = $A4 ;TEMP USED BY SERIAL ROUTINE COUNT = $A5 ;TEMP USED BY SERIAL ROUTINE FNLEN = $B7 ;FILENAME LENGTH FNADR = $BB ;FILENAME ADDRESS FA = $BA ;FILE PRIMARY ADDRESS SA = $B9 ;FILE SECONDARY ADDRESS STAL = $AA ;SAVE END ADDR LOW BYTE FOR SAVE ROUTINE STAH = $AB ;SAVE END ADDR HIGH BYTE FOR SAVE ROUTINE SAL = $AC ;START ADDR LOW BYTE FOR SAVE ROUTINE SAH = $AD ;START ADDR HIGH BYTE FOR SAVE ROUTINE EAL = $AE ;END ADDRESS LOW BYTE EAH = $AF ;END ADDRESS HIGH BYTE MEMUSS = $C3 ;USER SPECIFIED FILE LOAD ADDRESS VERCK = $0A ;LOAD OR VERIFY FLAG SPERR = 16 FNAME = $27 ;FILENAME MYSTATUS = $30 ;LOCATIONS USED BY THE NATIVE KIM-1 TAPE LOAD AND SAVE ROUTINES. ;I'LL USE THESE FOR DISK LOAD AND SAVE FOR CONSISTENCY OF USER ;EXPERIENCE. ID = $17F9 ;KIM-1 TAPE ID. USE AS FILENAME TSAL = $17F5 ;KIM-1 START ADDRESS LOW BYTE FOR TAPE ROUTINES TSAH = $17F6 ;KIM-1 START ADDRESS HIGH BYTE FOR TAPE ROUTINES TEAL = $17F7 ;KIM-1 END ADDRESS LOW FOR TAPE SAVE TEAH = $17F8 ;KIM-1 END ADDRESS HIGH FOR TAPE SAVE ; THE C64 KERNAL USED DC00 AND DD00 6526 ADDRESSES FOR THESE. ; CONVERTED TO USE 6530 LOCATIONS FOR TIMER AND IO TO RUN ON ; A KIM-1. PAD = $1700 ;PERIPHERAL DATA REGISTER A ON KIM-1 PADD = $1701 ;PERIPHERAL DATA DIR REGISTER A ON KIM-1 D2PRA = $1700 ;PERIPHERAL DATA REGISTER A ON C64 D2DDRA = $1701 ;PERIPHERAL DATA DIR REGISTER A ON C64 D1T2H = $1704 ;1T INTERVAL TIMER ON THE 6530 D64TH = $1706 ;64T INTERVAL TIMER ON THE 6530 D1ICR = $1707 ;6530 INTERVAL TIMER STATUS REGISTER * = $E000 ; TO BE LOADED INTO AN EPROM AND MAPPED IN AT $E000 LDINIT CLD SEI LDA #%00000111 STA PAD LDA #%00111111 STA PADD ; LDA #02 ;LENGTH OF OUR FILENAME IS 2 BYTES STA FNLEN LDA #01 ;SETTING THE SECONDARY ADDR TO 1 CAUSES IT TO USE THE STA SA ;FIRST TWO BYTES OF THE FILE AS THE SAVE ADDRESS. LDA #08 ;THIS IS THE DEVICE NUMBER. HARD CODING 8 FOR NOW. STA FA LDA #$27 STA FNADR LDA #$00 STA FNADR+1 STA EAL STA EAH STA STATUS STA MYSTATUS STA VERCK ;COPY KIM-1 NATIVE TAPE ROUTINE VALUES TO THE C64 KERNAL LOCATIONS LDA TSAL STA SAL LDA TSAH STA SAH ;******************************** ;* C64 KERNAL IEEE LOAD ROUTINE * ;******************************** ;LOAD FROM CBM IEEE DEVICE ; JSR CONVID LDY FNLEN ;MUST HAVE FILE NAME BNE LD25 ;YES...OK ; JMP ERROR8 ;MISSING FILE NAME ; LD25 LDX SA ;SAVE SA IN .X JSR LUKING ;TELL USER LOOKING LDA #$60 ;SPECIAL LOAD COMMAND STA SA JSR OPENI ;OPEN THE FILE ; LDA FA JSR TALK ;ESTABLISH THE CHANNEL LDA SA JSR TKSA ;TELL IT TO LOAD ; JSR ACPTR ;GET FIRST BYTE STA EAL ; LDA STATUS ;TEST STATUS FOR ERROR LSR A LSR A BCS LD90 ;FILE NOT FOUND... JSR ACPTR STA EAH ; TXA ;FIND OUT OLD SA BNE LD30 ;SA<>0 USE DISK ADDRESS LDA MEMUSS ;ELSE LOAD WHERE USER WANTS STA EAL LDA MEMUSS+1 STA EAH LD30 JSR LODING ;TELL USER LOADING ; LD40 LDA #$FD ;MASK OFF TIMEOUT AND STATUS STA STATUS ; ;JSR STOP ;STOP KEY? ;BNE LD45 ;NO... ; ;JMP BREAK ;STOP KEY PRESSED ; LD45 JSR ACPTR ;GET BYTE OFF IEEE TAX LDA STATUS ;WAS THERE A TIMEOUT? LSR A LSR A BCS LD40 ;YES...TRY AGAIN TXA LDY VERCK ;PERFORMING VERIFY? BEQ LD50 ;NO...LOAD LDY #0 CMP (EAL),Y ;VERIFY IT BEQ LD60 ;O.K.... LDA #SPERR ;NO GOOD...VERIFY ERROR JSR UDST ;UPDATE STATUS .BYTE $2C ;SKIP NEXT STORE ; LD50 STA (EAL),Y LD60 INC EAL ;INCREMENT STORE ADDR BNE LD64 INC EAH LD64 BIT STATUS ;EOI? BVC LD40 ;NO...CONTINUE LOAD ; JSR UNTLK ;CLOSE CHANNEL JSR CLSEI ;CLOSE THE FILE BCC LD180 ;BRANCH ALWAYS ; LD90 JMP ERROR4 ;FILE NOT FOUND ; OPENI LDA SA BMI OP175 ;NO SA...DONE LDY FNLEN BEQ OP175 ;NO FILE NAME...DONE ; LDA #0 ;CLEAR THE SERIAL STATUS STA STATUS ; LDA FA JSR LISTN ;DEVICE LA TO LISTEN ; LDA SA ORA #$F0 JSR SECND ; LDA STATUS ;ANYBODY HOME? BPL OP35 ;YES...CONTINUE ; ;THIS ROUTINE IS CALLED BY OTHER ;KERNAL ROUTINES WHICH ARE CALLED ;DIRECTLY BY OS. KILL RETURN ;ADDRESS TO RETURN TO OS. ; PLA PLA JMP ERROR5 ;DEVICE NOT PRESENT ; OP35 LDA FNLEN BEQ OP45 ;NO NAME...DONE SEQUENCE ; ;SEND FILE NAME OVER SERIAL ; LDY #0 OP40 LDA (FNADR),Y JSR CIOUT INY CPY FNLEN BNE OP40 ; OP45 JMP CUNLSN ;JSR UNLSN: CLC: RTS ;MODIFIED CUNLSN TO BRK INSTEAD OF RTS ; ;*************************** ;*HOMEBREW SUPPORT NONSENSE* ;*************************** LUKING PHA LDA #$01 STA MYSTATUS PLA RTS ; ERROR4 LDA #$04 STA MYSTATUS BRK ; ERROR5 LDA #$05 STA MYSTATUS BRK ; ERROR8 LDA #$08 STA MYSTATUS BRK ; LODING PHA LDA #$02 STA MYSTATUS PLA RTS ; SAVING PHA LDA #$03 STA MYSTATUS PLA RTS ; UDST ORA STATUS STA STATUS RTS ; CLSEI BIT SA BMI CLSEI2 LDA FA JSR LISTN LDA SA AND #$EF ORA #$E0 JSR SECND ; CUNLSN JSR UNLSN ;ENTRY FOR OPENI ; CLSEI2 CLC RTS ; LD180 CLC ;GOOD EXIT ; ; SET UP END LOAD ADDRESS ; LDX EAL LDY EAH ; OP175 CLC ;FLAG GOOD OPEN ;OP180 RTS ;EXIT IN PEACE OP180 BRK ; ;CONVERT TAPE ID TO ASCII AND STORE IN FNAME ; CONVID PHA LDA ID LSR A LSR A LSR A LSR A JSR ASCONV STA FNAME LDA ID JSR ASCONV STA FNAME+1 PLA RTS ; ;CONVERT LSD OF A TO ASCII ; ASCONV AND #$0F CMP #$0A CLC BMI HEX1 ADC #$07 HEX1 ADC #$30 RTS ; ;**************** ;* SAVE ROUTINE * ;**************** SVINIT CLD SEI LDA #%00000111 STA PAD LDA #%00111111 STA PADD LDA #02 ;LENGTH OF OUR FILENAME IS 2 BYTES STA FNLEN LDA #01 ;SETTING THE SECONDARY ADDR (SA) TO 1 CAUSES IT TO USE THE STA SA ;FIRST TWO BYTES OF THE FILE AS THE SAVE ADDRESS. LDA #08 ;THIS IS THE DEVICE NUMBER. HARD CODING 8 FOR NOW. STA FA LDA #$27 STA FNADR LDA #$00 STA FNADR+1 STA EAL STA EAH STA STATUS STA MYSTATUS STA VERCK JSR CONVID SAVESP LDX TEAL LDY TEAH STX EAL STY EAH LDA TSAL STA STAL STA SAL LDA TSAH STA STAH STA SAH ; SAVE LDA #$61 STA SA LDY FNLEN BNE SV25 ; JMP ERROR8 ;MISSING FILE NAME ; SV25 JSR OPENI JSR SAVING LDA FA JSR LISTN LDA SA JSR SECND LDY #0 JSR RD300 LDA SAL JSR CIOUT LDA SAH JSR CIOUT SV30 JSR CMPSTE ;COMPARE START TO END BCS SV50 ;HAVE REACHED END LDA (SAL),Y JSR CIOUT ;JSR STOP ;BNE SV40 ; ;BREAK JSR CLSEI ; LDA #0 ; SEC ; RTS ; SV40 JSR INCSAL ;INCREMENT CURRENT ADDR. BNE SV30 SV50 JSR UNLSN JSR CLSEI ; JMP CUNLSN ; RD300 LDA STAH ; RESTORE STARTING ADDRESS... STA SAH ;...POINTERS (SAH & SAL) LDA STAL STA SAL RTS ;COMPARE START AND END LOAD/SAVE ;ADDRESSES. SUBROUTINE CALLED BY ;TAPE READ, SAVE, TAPE WRITE ; CMPSTE SEC LDA SAL SBC EAL LDA SAH SBC EAH RTS ; INCSAL INC SAL BNE INCR INC SAH INCR RTS ; ;****************** ;* SERIAL LIBRARY * ;****************** ; ;COMMAND SERIAL BUS DEVICE TO TALK ; TALK ORA #$40 ;MAKE A TALK ADR .BYTE $2C ;SKIP TWO BYTES ; ;COMMAND SERIAL BUS DEVICE TO LISTEN ; LISTN ORA #$20 ;MAKE A LISTEN ADR ; XXX THE CALL TO RSP232 IS NOT NECESSARY ON THE KIM-1 ;JSR RSP232 ;PROTECT SELF FROM RS232 NMI'S LIST1 PHA ; BIT C3P0 ;CHARACTER LEFT IN BUF? BPL LIST2 ;NO... ; ;SEND BUFFERED CHARACTER ; SEC ;SET EOI FLAG ROR R2D2 ; JSR ISOUR ;SEND LAST CHARACTER ; LSR C3P0 ;BUFFER CLEAR FLAG LSR R2D2 ;CLEAR EOI FLAG ; LIST2 PLA ;TALK/LISTEN ADDRESS STA BSOUR ;SEI JSR DATAHI CMP #$3F ;CLKHI ONLY ON UNLISTEN BNE LIST5 JSR CLKHI ; LIST5 LDA D2PRA ;ASSERT ATTENTION ORA #$08 STA D2PRA ; ;ISOURA SEI ISOURA NOP JSR CLKLO ;SET CLOCK LINE LOW JSR DATAHI JSR W1MS ;DELAY 1 MS ;ISOUR SEI ;NO IRQ'S ALLOWED ISOUR NOP JSR DATAHI ;MAKE SURE DATA IS RELEASED JSR DEBPIA ;DATA SHOULD BE LOW BCS NODEV JSR CLKHI ;CLOCK LINE HIGH BIT R2D2 ;EOI FLAG TEST BPL NOEOI ;DO THE EOI ISR02 JSR DEBPIA ;WAIT FOR DATA TO GO HIGH BCC ISR02 ; ISR03 JSR DEBPIA ;WAIT FOR DATA TO GO LOW BCS ISR03 ; NOEOI JSR DEBPIA ;WAIT FOR DATA HIGH BCC NOEOI JSR CLKLO ;SET CLOCK LOW ; ;SET TO SEND DATA ; LDA #$08 ;COUNT 8 BITS STA COUNT ; ISR01 LDA D2PRA ;DEBOUNCE THE BUS CMP D2PRA BNE ISR01 ASL A ;SET THE FLAGS BCC FRMERR ;DATA MUST BE HI ; ROR BSOUR ;NEXT BIT INTO CARRY BCS ISRHI JSR DATALO BNE ISRCLK ISRHI JSR DATAHI ISRCLK JSR CLKHI ;CLOCK HI NOP NOP NOP NOP LDA D2PRA AND #$FF-$20 ;DATA HIGH ORA #$10 ;CLOCK LOW STA D2PRA DEC COUNT BNE ISR01 LDA #$04 ;SET TIMER FOR 1MS STA D1T2H ;LDA #TIMRB ;TRIGGER TIMER ; XXX NOT NEEDED ON KIM-1 ;STA D1CRB ;LDA D1ICR ;CLEAR THE TIMER FLAGS<<<<<<<<<<<<< ISR04 LDA D1ICR AND #$02 BNE FRMERR JSR DEBPIA BCS ISR04 ;CLI ;LET IRQ'S CONTINUE RTS ; NODEV ;DEVICE NOT PRESENT ERROR LDA #$80 .BYTE $2C FRMERR ;FRAMING ERROR LDA #$03 CSBERR JSR UDST ;COMMODORE SERIAL BUSS ERROR ENTRY ;CLI ;IRQ'S WERE OFF...TURN ON CLC ;MAKE SURE NO KERNAL ERR BCC DLABYE ;TURN ATN OFF ,RELEASE ALL LINES ; ;SEND SECONDARY ADDRESS AFTER LISTEN ; SECND STA BSOUR ;BUFFER CHARACTER JSR ISOURA ;SEND IT ;RELEASE ATTENTION AFTER LISTEN ; SCATN LDA D2PRA AND #$FF-$08 STA D2PRA ;RELEASE ATTENTION RTS ;TALK SECOND ADDRESS ; TKSA STA BSOUR ;BUFFER CHARACTER JSR ISOURA ;SEND SECOND ADDR TKATN ;SHIFT OVER TO LISTENER ;SEI ;NO IRQ'S HERE JSR DATALO ;DATA LINE LOW JSR SCATN JSR CLKHI ;CLOCK LINE HIGH JSR/RTS TKATN1 JSR DEBPIA ;WAIT FOR CLOCK TO GO LOW BMI TKATN1 ;CLI ;IRQ'S OKAY NOW RTS ;BUFFERED OUTPUT TO SERIAL BUS ; CIOUT BIT C3P0 ;BUFFERED CHAR? BMI CI2 ;YES...SEND LAST ; SEC ;NO... ROR C3P0 ;SET BUFFERED CHAR FLAG BNE CI4 ;BRANCH ALWAYS ; CI2 PHA ;SAVE CURRENT CHAR JSR ISOUR ;SEND LAST CHAR PLA ;RESTORE CURRENT CHAR CI4 STA BSOUR ;BUFFER CURRENT CHAR CLC ;CARRY-GOOD EXIT RTS ;SEND UNTALK COMMAND ON SERIAL BUS ; ;UNTLK SEI UNTLK NOP JSR CLKLO LDA D2PRA ;PULL ATN ORA #$08 STA D2PRA LDA #$5F ;UNTALK COMMAND .BYTE $2C ;SKIP TWO BYTES ;SEND UNLISTEN COMMAND ON SERIAL BUS ; UNLSN LDA #$3F ;UNLISTEN COMMAND JSR LIST1 ;SEND IT ; ; RELEASE ALL LINES DLABYE JSR SCATN ;ALWAYS RELEASE ATN ; DELAY THEN RELEASE CLOCK AND DATA ; DLADLH TXA ;DELAY APPROX 60 US LDX #10 DLAD00 DEX BNE DLAD00 TAX JSR CLKHI JMP DATAHI ;INPUT A BYTE FROM SERIAL BUS ; ACPTR SEI ;NO IRQ ALLOWED LDA #$00 ;SET EOI/ERROR FLAG STA COUNT JSR CLKHI ;MAKE SURE CLOCK LINE IS RELEASED ACP00A JSR DEBPIA ;WAIT FOR CLOCK HIGH BPL ACP00A ; EOIACP LDA #$04 ;SET TIMER 2 FOR 256US STA D64TH ;LDA #TIMRB ; XXX NOT NEEDED ON KIM-1 ;STA D1CRB JSR DATAHI ;DATA LINE HIGH (MAKES TIMMING MORE LIKE VIC-20 ;LDA D1ICR ;CLEAR THE TIMER FLAGS<<<<<<<<<<<< ACP00 BIT D1ICR BMI ACP00B ;RAN OUT..... JSR DEBPIA ;CHECK THE CLOCK LINE BMI ACP00 ;NO NOT YET BPL ACP01 ;YES..... ; ACP00B LDA COUNT ;CHECK FOR ERROR (TWICE THRU TIMEOUTS) BEQ ACP00C LDA #2 JMP CSBERR ;ST = 2 READ TIMEOUT ; ; TIMER RAN OUT DO AN EOI THING ; ACP00C JSR DATALO ;DATA LINE LOW JSR CLKHI ;DELAY AND THEN SET DATAHI (FIX FOR 40US C64) LDA #$40 JSR UDST ;OR AN EOI BIT INTO STATUS INC COUNT ;GO AROUND AGAIN FOR ERROR CHECK ON EOI BNE EOIACP ; ; DO THE BYTE TRANSFER ; ACP01 LDA #08 ;SET UP COUNTER STA COUNT ; ACP03 LDA D2PRA ;WAIT FOR CLOCK HIGH CMP D2PRA ;DEBOUNCE BNE ACP03 ASL A ;SHIFT DATA INTO CARRY BPL ACP03 ;CLOCK STILL LOW... ROR BSOUR1 ;ROTATE DATA IN ; ACP03A LDA D2PRA ;WAIT FOR CLOCK LOW CMP D2PRA ;DEBOUNCE BNE ACP03A ASL A BMI ACP03A DEC COUNT BNE ACP03 ;MORE BITS..... ;...EXIT... JSR DATALO ;DATA LOW BIT STATUS ;CHECK FOR EOI BVC ACP04 ;NONE... ; JSR DLADLH ;DELAY THEN SET DATA HIGH ; ACP04 LDA BSOUR1 ;CLI ;IRQ IS OK CLC ;GOOD EXIT RTS ; CLKHI ;SET CLOCK LINE HIGH (INVERTED) LDA D2PRA AND #$FF-$10 STA D2PRA RTS ; CLKLO ;SET CLOCK LINE LOW (INVERTED) LDA D2PRA ORA #$10 STA D2PRA RTS ; DATAHI ;SET DATA LINE HIGH (INVERTED) LDA D2PRA AND #$FF-$20 STA D2PRA RTS ; DATALO ;SET DATA LINE LOW (INVERTED) LDA D2PRA ORA #$20 STA D2PRA RTS ; DEBPIA LDA D2PRA ;DEBOUNCE THE PIA CMP D2PRA BNE DEBPIA ASL A ;SHIFT THE DATA BIT INTO THE CARRY... RTS ;...AND THE CLOCK INTO NEG FLAG ; W1MS ;DELAY 1MS USING LOOP TXA ;SAVE .X LDX #200-16 ;1000US-(1000/500*8=#40US HOLDS) W1MS1 DEX ;5US LOOP BNE W1MS1 TAX ;RESTORE .X RTS