1 8080 MACRO ASSEMBLER, VER 3.0 ERRORS = 0 + 19:22 02/29/2017 + PAGE 1 ; MBL - MULTI BOOT LOADER FOR THE ALTAIR 8800 ; ; DISAASEMBLED AND COMMENTED BY GEOFF HARRISON (GHOV SOLIVANT COM) ; ; THIS IS A BOOT LOADER THAT CAN BE LOACATED IN ROM AND WHICH ; CAN READ ANY OF THE PUNCHED TAPE FORMATS THAT MITS DESIGNED. ; IT RUNS OUT OF ROM BY CREATING A READBYTE ROUTINE IN RAM WHICH ; IS CUSTOMIZED FOR WHATEVER I/O BOARD THE USER SPECIFIES AT ; RUN TIME ON THE FRONT PANEL SWITCHES. IT THEN SKIPS OVER THE ; LEADIN BYTES AND THE SECOND STAGE LOADER WHICH ALWAYS PRECEED ; THE PAYLOAD ON A MITS TAPE. SINCE IT DOESN'T USE THE ; SECOND STAGE LOADER, IT DOESN'T CARE WHICH OF SEVERAL POSSIBLE ; VERSIONS OF TAPE IT IS LOADING. NORMALLY YOU HAVE TO BE SURE ; TO USE THE CORRECT 1ST STAGE LOADER FOR THE TAPE YOU ARE LOADING, ; WITH THE MBL IT DOESN'T MATTER. AFTER SKIPPING THE 2ND STAGE ; LOADER ON THE TAPE, IT STARTS READING AND STORING PAYLOAD ; BYTES AND CHECKING THAT THE CHECKSUM IS CORRECT FOR EACH PACKET ; OF BYTES READ. WHEN THE ENTIRE PAYLOAD HAS BEEN READ INTO MEMORY, ; IT READS THE ENTRY POINT FOR THE PROGRAM FROM THE TAPE AND JUMPS ; TO THAT LOCATION. ; ; THE FORMAT OF A MITS PAPER TAPE IS: ; - SOME NUMBER OF IDENTICAL BYTES, EACH CONTAINING ; THE LENGTH (N) OF THE STAGE2 LOADER ; - N BYTES OF STAGE 2 LOADER ; - OPTIONALLY SOME NUMBER OF NULLS ; - ONE OR MORE LOAD RECORDS (SEE BELOW) ; - AN EOF RECORD (SEE BELOW) ; ; A LOAD RECORD CONSISTS OF: ; 074 - SYNC BYTE (HEX 03CH) ; NNN - # BYTES IN RECORD ; LLL - LOW BYTE OF LOAD ADDRESS ; HHH - HIGH BYTE OF LOAD ADDRESS ; - NNN BYTES OF PROGRAM DATA (THE PAYLOAD) ; CCC - CHECKSUM BYTE ; (CHECKSUM INCLUDES LLL & HHH) ; THERE WILL BE 1 OR MORE PROG LOAD RECORDS, ; EACH ONE WITH UP TO 256 BYTES OF PAYLOAD ; BYTES. ; ; THE EOF RECORD CONSISTS OF: ; 0170 - SYNC BYTE (HEX 078H) ; LLL - LOW BYTE OF START ADDRESS ; HHH - HIGH BYTE OF START ADDRESS ; ; BEFORE EXECUTING THIS PROGRAM, THE FRONT PANEL SENSE SWITCHES ; MUST BE SET TO INDICATE WHAT DEVICE TO READ THE TAPE FROM AND ; WHAT DEVICE THE TERMINAL IS ATTACHED TO. THIS PROGRAM USES ; A11..A8 TO DETERMINE THE DEVICE ATTACHED TO THE TAPE READER. ; IF THE PAYLOAD IS NOT EARLIER THAN BASIC 4.0, IT USES A15..A12 1 8080 MACRO ASSEMBLER, VER 3.0 ERRORS = 0 + 19:22 02/29/2017 + PAGE 2 ; TO DETERMINE WHERE THE TERMINAL DEVICE IS. ; POSSIBLE SWITCH VALUES ARE ; ; DEVICE SWITCH VALUE ; 2SIO (2 STOP BITS) 0000B ; 2SIO (1 STOP BIT) 0001B ; SIO 0010B ; ACR 0011B ; 4PIO 0100B ; PIO 0101B ; HSR 0110B ; ; IF A VALUE LARGER THAN 7 IS ENTERED THIS PROGRAM WILL RETURN ; AN ERROR. ; ; PRIOR TO BASIC 4.0, MITS USED DIFFERENT SENSE SWITCH SETTINGS ; TO SPECIFY THE TERMINAL DEVICE. YOU SHOULD STILL BE ABLE TO ; LOAD AN OLDER TAPE WITH THIS LOADER BY SETTING THE SWITCHES AS ; ABOVE, STOPPING THE PROGRAM AFTER IT LOADS AND STARTS, CHANGING ; THE SENSE SWITCHES (SEE THE APPROPRIATE MITS MANUAL FOR SWITCH ; SETTINGS) AND RESTARTING THE PROGRAM AT ITS ENTRY POINT (E.G. ; 00000H FOR BASIC 3.2). ; ; THIS LISTING WAS GENERATED FROM A HEX DUMP OF MBL PROVIDED BY ; GRANT STOCKLY. THE ASSEMBLY CODE AND COMMENTS WERE REVERSE ; ENGINEERED FROM THAT DUMP BY GEOFF HARRISON. ; DEFAULT LOCATION IS AT 0FE00H. MAY BE ASSEMBLED TO RUN ; AT ANY LOCATION. ; ; ASSEMBLER SYNTAX IS FOR THE SPASM ASSEMBLER. TO ASSEMBLE USE: ; SPASM MBL /F ; SLINK MBL=MBL.OBJ /C:0FE00 ; ; FOR OTHER ASSEMBLERS, UNCOMMENT THE FOLLOWING LINE AND ; (POSSIBLY) CHANGE THE SYNTAX OF ORG, DB, ETC. ; FE00 ORG 0FE00H ;---------------------------------------------------------- ; WE DON'T KNOW WHAT I/O CARDS ARE IN THE SYSTEM, SO ; TRY TO INITIALIZE JUST ABOUT ANYTHING MITS HAD AVAILABLE ; AT THE TIME. ; FE00 F3 DI FE01 AF XRA A FE02 D320 OUT 020H FE04 D321 OUT 021H FE06 D324 OUT 024H FE08 D325 OUT 025H FE0A D326 OUT 026H 1 8080 MACRO ASSEMBLER, VER 3.0 ERRORS = 0 + 19:22 02/29/2017 + PAGE 3 FE0C D322 OUT 022H FE0E 2F CMA FE0F D323 OUT 023H FE11 D327 OUT 027H FE13 3E0C MVI A,00CH FE15 D324 OUT 024H FE17 3E2C MVI A,02CH FE19 D320 OUT 020H FE1B D322 OUT 022H FE1D D326 OUT 026H FE1F 3E03 MVI A,003H FE21 D327 OUT 027H FE23 D310 OUT 010H FE25 3E11 MVI A,011H FE27 D310 OUT 010H ;---------------------------------------------------------- ; FIND TOP OF RAM. ASSUMES THAT THERE IS NOT 64K OF RAM ; AVAILABLE, A REASONABLE ASSUMPTION GIVEN THAT THIS ROUTINE ; RESIDES IN ROM SOMEWHERE AT THE TOP OF MEMORY. ; FE29 21FFFF LXI H, 0FFFFH FE2C 23 SCANRAM: INX H ; POINT @ NEXT BYTE FE2D 7E MOV A,M ; GET IT FE2E 47 MOV B,A ; SAVE IT FE2F 2F CMA ; INVERT IT FE30 77 MOV M,A ; TRY TO WRITE IT BACK OUT FE31 BE CMP M ; SEE IF IT WROTE OUT CORRECTLY FE32 70 MOV M,B ; RESTORE THE BYTE TO ITS ORIG VALUE FE33 CA2CFE JZ SCANRAM ; LOOP IF THE BYTE WROTE CORRECTLY ; SOMETHING'S WRONG IF THE FAILURE TO WRITE TO RAM ; HAPPENED ON OTHER THAN A PAGE BOUNDARY FE36 AF XRA A ; A = 0 FE37 BD CMP L FE38 C2C1FE JNZ MERROR ; IF L != 0 GO TO 'M' ERROR HANDLER ; HL NOW POINTS TO THE LAST WRITABLE BYTE IN RAM PLUS 1. ; SUBTRACT 14 TO MAKE ROOM FOR A STACK & INITIALIZE SP. FE3B 01F2FF LXI B,0FFF2H FE3E 09 DAD B ; HL += BC FE3F F9 SPHL ; SP = HL FE40 09 DAD B ; SET HL TO POINT TO WHAT WILL BE ; THE START OF THE READBYTE ROUTINE. FE41 E5 PUSH H ; SAVE THE START ADDRESS ON THE STACK. FE42 DBFF IN 0FFH ; READ FRONT PANEL SWITCHES FE44 E60F ANI 00FH ; MASK LOWER 4 BITS FE46 FE07 CPI 007H ; SWITCHES SET TO >= 7? FE48 F2D7FE JP IERROR ; Y - GO TO 'I' ERROR HANDLER 1 8080 MACRO ASSEMBLER, VER 3.0 ERRORS = 0 + 19:22 02/29/2017 + PAGE 4 ; POINT HL AT THE NTH ENTRY IN THE MOD TABLE, ; WHERE N = THE FRONT PANEL SWITCH SETTING FE4B 21EBFE LXI H, TABLE1 ; POINT HL TO START OF THE MOD TABLE FE4E 04 INR B ; B CURRENTLY CONTAINS 0FFH, INC IT TO 0 FE4F 4F MOV C,A ; FE50 87 ADD A ; C = A * 3 FE51 81 ADD C ; / FE52 4F MOV C,A ; / FE53 09 DAD B ; HL += BC ;---------------------------------------------------------- ; CONSTRUCT AN INPUT FUNCTION ON THE STACK. ; SINCE THIS IS A PUSH DOWN STACK, THE ROUTINE IS BUILT IN REVERSE. ; WHEN FINISHED, THE ROUTINE WILL LOOK LIKE THIS. (XX VALUES ARE ; CALCULATED ON THE FLY OR READ FROM THE MOD TABLE. THE ROUTINE ; HAS TO BE BUILT DYNAMICALLY LIKE THIS BECAUSE DIFFERENT I/O CARDS ; REQUIRE DIFFERENT CODE TO READ THEIR DATA AND STATUS. THE USER ; SPECIFIED WHICH CARD IS IN USE ON THE FRONT PANEL SWITCHES.) ; READBYTE: ; DB XX IN XX ; CHECK PORT STATUS ; E6 XX ANI XX ; XX LO HI JZ/JNZ READBYTE ; LOOP 'TILL BYTE ARRIVES ; DB XX IN XX ; GET INPUT BYTE ; F5 PUSH PSW ; SAVE IT ; 80 ADD B ; UPDATE CHECKSUM IN B ; 47 MOV B,A ; F1 POP PSW ; RETRIEVE INPUT BYTE ; C9 RET ; RETURN A=BYTE, B=CHECKSUM ; FE54 D1 POP D ; DE = THE START ADRESS OF THIS ROUTINE ; CONSTRUCT RET; POP PSW FE55 01F1C9 LXI B,0C9F1H FE58 C5 PUSH B ; CONSTRUCT MOV B,A; ADD B FE59 018047 LXI B,04780H FE5C C5 PUSH B ; CONSTRUCT PUSH PSW; INPUT PORT RETRIEVED FROM MOD TABLE FE5D 06F5 MVI B,0F5H FE5F 4E MOV C,M FE60 79 MOV A,C FE61 C5 PUSH B ; CONSTRUCT IN (USED WITH PORT CONSTRUCTED ABOVE); HIGH BYTE OF FE62 06DB MVI B,0DBH FE64 4A MOV C,D FE65 C5 PUSH B 1 8080 MACRO ASSEMBLER, VER 3.0 ERRORS = 0 + 19:22 02/29/2017 + PAGE 5 ; CONSTRUCT LOW BYTE OF JMP ; JZ/JNZ (FROM MOD TABLE) FE66 43 MOV B,E FE67 23 INX H FE68 4E MOV C,M FE69 C5 PUSH B ; CONSTRUCT ANI MASK FROM MOD TABLE FE6A 23 INX H FE6B 46 MOV B,M FE6C 0EE6 MVI C,0E6H FE6E C5 PUSH B ; CONSTRUCT IN PORT STATUS ADDRESS (PORT NUMBER - 1) FE6F 3D DCR A FE70 47 MOV B,A FE71 0EDB MVI C,0DBH FE73 C5 PUSH B ;---------------------------------------------------------- ; READ A STREAM OF INPUT BYTES. ; FE74 EB XCHG ; HL = START OF READBYTE ROUTINE, DE = JUNK ; ??????????????????????????????????????????????????? FE75 3E04 MVI A,004H ; WHY ARE WE SENDING 04H TO DEVICE 027H? FE77 D327 OUT 027H ; IN FACT, WHAT IS DEVICE 027H? ANYONE KNOW? IS ; 88-HSR? PERHAPS WE'RE SWITCHING ON THE DRIVE ; ??????????????????????????????????????????????????? ; SKIP OVER LEADIN BYTES. FE79 CDA5FE CALL LINK ; FLUSH INPUT BUFFER FE7C CDA5FE CALL LINK ; GET A BYTE FE7F 4F MOV C,A ; REMEMBER IT FE80 CDA5FE LEADINSKIP: CALL LINK ; GET ANOTHER BYTE FE83 B9 CMP C FE84 CA80FE JZ LEADINSKIP ; LOOP UNTIL WE RECEIVE A DIFFERENT BYTE VALUE ; AT THIS POINT, C CONTAINS THE FIRST LEADIN BYTE ; THAT WAS ON THE TAPE, WHICH SHOULD REPRESENT THE ; LENGTH OF THE STAGE 2 LOADER. ; SKIP OVER STAGE 2 LOADER. FE87 0D DCR C FE88 CDA5FE STAGE2SKIP: CALL LINK ; GET A BYTE FE8B 0D DCR C FE8C C288FE JNZ STAGE2SKIP ; LOOP WHILE C > 0 ; NOW WE'VE SKIPPED OVER ALL THE UNNEEDED STUFF, START ; LOOKING FOR THE FIRST LOAD RECORD. FE8F CDA5FE FINDTOKEN: CALL LINK ; GET A BYTE FE92 FE3C CPI 03CH ; IS IT A LOAD RECORD TOKEN? FE94 CAA6FE JZ LOADRECORD ; Y - GO AND PROCESS A LOAD RECORD FE97 FE78 CPI 078H ; IS IT AN EOF TOKEN? 1 8080 MACRO ASSEMBLER, VER 3.0 ERRORS = 0 + 19:22 02/29/2017 + PAGE 6 FE99 C28FFE JNZ FINDTOKEN ; N - KEEP LOOKING ; GOT AN EOF TOKEN. READ NEXT TWO BYTES AS PROGRAM ; START ADDRESS AND JUMP TO THAT ADDRESS. FE9C CDA5FE EOF: CALL LINK ; GET PROG START LOW FE9F 4F MOV C,A FEA0 CDA5FE CALL LINK ; GET PROG START HIGH FEA3 69 MOV L,C FEA4 67 MOV H,A ; THIS IS MOSTLY USED TO CALL THE BYTE INPUT ROUTINE ; ON THE STACK, BUT IS ALSO USED TO JUMP TO THE ENTRY ; POINT OF THE DOWNLOADED PROGRAM. FEA5 E9 LINK: PCHL ; JMP TO (HL) ; PROCESS A LOAD RECORD FEA6 CDA5FE LOADRECORD: CALL LINK ; GET BYTE COUNT IN THIS RECORD FEA9 4F MOV C,A ; SAVE IT FEAA 0600 MVI B,000H ; INITIALIZE CHECKSUM FEAC CDA5FE CALL LINK ; GET LOAD ADDRESS LOW FEAF 5F MOV E,A FEB0 CDA5FE CALL LINK ; GET LOAD ADDRESS HIGH FEB3 57 MOV D,A FEB4 7A LOREC2: MOV A,D FEB5 BC CMP H ; ARE THE INCOMING BYTES ABOUT TO ; OVERWRITE THE READBYTE ROUTINE? FEB6 3E4F MVI A,04FH ; PREPARE TO SEND 'O', IF NECESSARY FEB8 CAD9FE JZ ERREXIT ; Y - ERROR EXIT FEBB CDA5FE CALL LINK ; N - GET ANOTHER BYTE FEBE EB XCHG ; HL = DEST POINTER, DE = START OF READBYTE FEBF 77 MOV M,A ; STORE RECEIVED BYTE AT DESTINATION FEC0 BE CMP M ; DID IT STORE CORRECTLY? FEC1 3E4D MERROR: MVI A,04DH ; PREPARE TO SEND 'M', IF NECESSARY FEC3 C2D9FE JNZ ERREXIT ; N - ERROR EXIT FEC6 23 INX H ; Y - INCREMENT DESTINATION POINTER FEC7 EB XCHG ; HL = START OF READBYTE, DE = DEST POINTER FEC8 0D DCR C ; DECREMENT BYTE COUNTER FEC9 C2B4FE JNZ LOREC2 ; IF NOT 0 THEN LOOP TO GET MORE BYTES FECC 48 MOV C,B ; SAVE CALCULATED CHECKSUM VALUE BEFORE WE UPDAT FECD CDA5FE CALL LINK ; GET EXPECTED CHECKSUM FROM INPUT STREAM FED0 B9 CMP C ; DOES IT MATCH OUR CALCULATED SUM? FED1 CA8FFE JZ FINDTOKEN ; Y - LOOK FOR MORE RECORDS ON THE TAPE FED4 3E43 MVI A,043H ; N - PREPARE TO SEND 'C' ERROR FED6 01 DB 001H ; LXI - HIDES NEXT TWO BYTES FED7 3E IERROR: DB 03EH ; MVI A, 049H ; PREPARE TO SEND 'I' FED8 49 DB 049H ; STORE AN ERROR CODE AND THE ADDRESS @ WHICH IT HAPPENED IN ; THE FIRST 3 BYTES OF RAM, THEN LOOP FOREVER SENDING THE 1 8080 MACRO ASSEMBLER, VER 3.0 ERRORS = 0 + 19:22 02/29/2017 + PAGE 7 ; ERROR CODE TO ALL POSSIBLE TERMINAL DEVICES. ; FED9 320000 ERREXIT: STA 00000H FEDC 220100 SHLD 00001H FEDF FB EI FEE0 D301 FOREVER: OUT 001H FEE2 D311 OUT 011H FEE4 D305 OUT 005H FEE6 D323 OUT 023H FEE8 C3E0FE JMP FOREVER ;---------------------------------------------------------- ; MOD TABLE. ; THIS IS A TABLE OF PORT ADDRESSES, COMMANDS FOR CHECKING ; THE PORT STATUS (JZ/JNZ), AND STATUS MASKS FOR SEVERAL ; I/O BOARDS. THE VALUES ARE STUFFED INTO THE READBYTE ; ROUTINE AT RUNTIME TO CUSTOMIZE IT FOR THE HARDWARE ; BEING USED TO LOAD THE TAPE. ; FEEB 11CA01 TABLE1: DB 011H, 0CAH, 001H ; 2SIO (2 STOP BITS) FEEE 11CA01 DB 011H, 0CAH, 001H ; 2SIO (1 STOP BIT) FEF1 01C201 DB 001H, 0C2H, 001H ; SIO FEF4 07C201 DB 007H, 0C2H, 001H ; ACR FEF7 21CA80 DB 021H, 0CAH, 080H ; 4PIO FEFA 05CA02 DB 005H, 0CAH, 002H ; PIO FEFD 25CA40 DB 025H, 0CAH, 040H ; HSR END NO PROGRAM ERRORS 1 8080 MACRO ASSEMBLER, VER 3.0 ERRORS = 0 + 19:22 02/29/2017 + PAGE 8 SYMBOL TABLE * 01 A 0007 B 0000 C 0001 D 0002 E 0003 EOF FE9C * ERREX FED9 FINDT FE8F FOREV FEE0 H 0004 IERRO FED7 L 0005 LEADI FE80 LINK FEA5 LOADR FEA6 LOREC FEB4 M 0006 MERRO FEC1 PSW 0006 SCANR FE2C SP 0006 STAGE FE88 TABLE FEEB