;18 JAN 77. BRH. CREATED. ; ;*********************************************************** ;*********************************************************** ;**** **** ;**** TARBELL BOOTSTRAP LOADER **** ;**** **** ;**** (C) COPYRIGHT 1977, IMSAI MFG CORP **** ;**** SAN LEANDRO, CALIFORNIA **** ;**** **** ;*********************************************************** ;*********************************************************** ; ; THIS PROGRAM HAS SEVERAL SPECIAL CONSTRAINTS: ; ; 1. IT MUST BE CAPABLE OF RUNNING IN PROM. ; ; 2. IT MUST USE NO RAM OTHER THAN THAT INTO WHICH THE ; BOOTED PROGRAM IS LOADED; IN PARTICULAR, IT MUST NOT ; USE A STACK. ; ; 3. IT MUST RUN IN 512 BYTES, STARTING AT FA00. ; ; 4. IT MUST NOT INCLUDE BYTES 'FA' AND 'FB' AS ANYTHING ; BUT HI ADDRESS BYTES, SO IT MAY BE RELOCATED. THIS ; MEANS THAT THE INSTRUCTIONS 'JM' AND 'EI' MUST NOT ; BE USED, AND THAT 'FA' AND 'FB' MUST NOT OCCUR IN ; THE 2ND BYTE OF AN INSTRUCTION. ; CRI EQU 0 ;CASSETTE PORT CRL EQU 3 ;CONTROL PORT CRY EQU 4 ;CASSETTE READY BIT ; ORG 0FA00H START: XRA A ;TURN ON LIGHTS... OUT 0FFH MVI A,60H ;SET MIO TO READ BY BIT... OUT CRL SYNC0: IN CRL ANI CRY JZ SYNC0 IN CRI ;READ THEM CPI 0E6H ;ARE THEY A SYNC JNZ SYNC0 ;WAIT TILL A SYNC IS FOUND MVI A,20H ;SET TO READ BY BYTE... OUT CRL MVI B,31 ;# OF OTHER SYNC'S AT START OF FILE SYNC1: IN CRL ;WAIT TILL A BYTE IS READY... ANI CRY JZ SYNC1 IN CRI ;READ THE BYTE CPI 0E6H ;IS IT A SYNC? JNZ START ;START OVER IF NOT DCR B ;COUNT SYNC'S JNZ SYNC1 ;LOOP UNTIL STRIP DONE TYPE: IN CRL ;READ RECORD TYPE... ANI CRY JZ TYPE IN CRI DCR A ;IS IT 1 (ABSOLUTE BINARY OBJECT)? JNZ START ;START OVER IF NOT COUNT: IN CRL ;READ RECORD COUNT... ANI CRY JZ COUNT IN CRI CPI 11 ;IS IT 11 (5-BYTE NAME + 3 2-BYTE ADDR'S) JNZ START ;START OVER IF NOT MVI B,5 ;INIT COUNTER OF BYTES IN NAME LXI D,0 ;INIT CHECKSUM NAME: IN CRL ;READ A BYTE... ANI CRY JZ NAME IN CRI ADD E ;ADD TO CHECKSUM MOV E,A MVI A,0 ADC D MOV D,A DCR B ;COUNT LETTERS JNZ NAME ;READ 5 OF THEM ADDS0: IN CRL ;READ LO BYTE OF START ADDRESS... ANI CRY JZ ADDS0 IN CRI MOV L,A ;SAVE IN L ADD E ;ADD TO CHECKSUM... MOV E,A MVI A,0 ADC D MOV D,A ADDS1: IN CRL ;READ HI BYTE OF START ADDRESS... ANI CRY JZ ADDS1 IN CRI MOV H,A ;SAVE IN H ADD E ;ADD TO CHECKSUM... MOV E,A MVI A,0 ADC D MOV D,A SPHL ;SAVE START ADDRESS IN SP ADDE0: IN CRL ;READ LO BYTE OF END ADDRESS... ANI CRY JZ ADDE0 IN CRI MOV L,A ;SAVE IN L ADD E ;ADD TO CHECKSUM... MOV E,A MVI A,0 ADC D MOV D,A ADDE1: IN CRL ;READ HI BYTE OF END ADDRESS... ANI CRY JZ ADDE1 IN CRI MOV H,A ;SAVE IN H ADD E ;ADD TO CHECKSUM... MOV E,A MVI A,0 ADC D MOV D,A MVI B,2 ;READ LAST 2 BYTES AND ADD TO CHECKSUM... ADDX: IN CRL ANI CRY JZ ADDX IN CRI ADD E MOV E,A MVI A,0 ADC D MOV D,A DCR B JNZ ADDX XCHG ;PUT CHECKSUM IN HL, END ADDRESS IN DE CHECB: IN CRL ;READ HI CHECKSUM BYTE INTO B... ANI CRY JZ CHECB IN CRI MOV B,A CHECC: IN CRL ;READ LO CHECKSUM BYTE INTO C... ANI CRY JZ CHECC IN CRI MOV C,A DAD B ;ADD TO ACCUMULATED CHECKSUM MOV A,H ;IS RESULT 0?... ORA L JNZ START ;ABORT IF NOT DAD SP ;GET START ADDRESS INTO HL MOV A,E ;SUBTRACT START FROM END ADDRESS AND SUB L ; PUT RESULT IN HL... MOV L,A MOV A,D SBB H MOV H,A DAD H ;DOUBLE IT MOV C,H ;PUT RECORD COUNT IN C... INR C LXI H,0 ;PUT START ADDRESS IN HL... DAD SP RECOR: MOV A,H ;PUT HIGH ADDRESS BYTE IN LIGHTS... CMA OUT 0FFH RTYPE: IN CRL ;READ RECORD TYPE.. ANI CRY JZ RTYPE IN CRI CPI 81H ;IS IT AN ABSOLUTE BINARY OBJECT JNZ START ;ABORT IF SO RCOUN: IN CRL ;READ BYTE COUNT... ANI CRY JZ RCOUN IN CRI MOV B,A ;PUT IN B LXI D,0 ;INIT CHECKSUM RDATA: IN CRL ANI CRY JZ RDATA IN CRI MOV M,A ;STASH IT... INX H ADD E ;ADD TO CHECKSUM... MOV E,A MVI A,0 ADC D MOV D,A DCR B ;COUNT BYTES JNZ RDATA ;LOOP TILL ALL DATA IN RCHEK: IN CRL ;READ HI CHECKSUM BYTE... ANI CRY JZ RCHEK IN CRI MOV B,A ;SAVE IT IN B RCHEL: IN CRL ;READ LO CHECKSUM BYTE... ANI CRY JZ RCHEL IN CRI ADD E ;ADD TO LO BYTE OF ACCUMULATED CHECKSUM JNZ START ;ABORT IF ERROR MOV A,B ;GET HI CHECKSUM BYTE BACK INTO A ADC D ;ADD TO HI BYTE OF ACCUMULATED CHECKSUM JNZ START ;ABORT IF ERROR DCR C ;COUNT RECORDS JNZ RECOR ;LOOP TILL ALL READ XRA A ;TURN LIGHTS ON (LIKE AFTER A RESET)... OUT 0FFH LXI H,0 ;GET START ADDRESS INTO HL... DAD SP PCHL ;OKAY BUB, HEAD OUT ; END