1 .title Dual-Density bootstrap for RX02 2 3 ; This bootstrap is derived from the RX211/RXV21 4 ; bootstrap that appears in the RX01/RX02 Pocket Service 5 ; Gude (DEC order number EK-RX012-PS-002). 6 ; 7 ; It has been modified so that: 8 ; * It can be used for unit 0 or unit 1 9 ; * It will first attempt to boot a double-density disk. 10 ; If that fails, it will then attempt to boot a 11 ; single-density disk. 12 ; 13 ; The code shown below is for unit 0. to boot from unit 1: 14 ; * change the word at 0010036 from 000407 to 000427 15 ; * change the word at 0010132 from 000000 to 000001 16 ; 17 ; Malcolm MacLeod - 11 June 2017 18 ; 19 ; Documentation and boot logic 20 ; Joerg Hoppe - Nov 2022 21 22 23 177170 rx2cs = 177170 ; RXV21 control/status register 24 177172 rx2db = 177172 ; RXV21 data buffer register 25 000200 wrdcnt = ^D128 ; 128 for DBL-DEN, 64 for SGL-DEN 26 100240 mask = 100240 ; Bit 15=ERR, 7=XFER-RQST, 5=DONE 27 28 .asect 29 ; ---- Simple boot drive 0 from 0 30 000000 . = 0 31 000000 000137 010000 jmp @#start0 32 33 ; ---- Reboot drive 0 on power event 34 000024 . = 24 ; Power ON/OFF 35 000024 010000 .word start0 ; PC 36 000026 000340 .word 340 ; PSW priority level 7 37 38 39 ; ----- Main boot addresses 40 010000 .=10000 ; arbitrary position > 3000 41 42 ; On boot from #0 implemented 43 start: 44 ; ; 2 unit numbers => 2 entry addresses 45 start0: 46 ; mov #0,r0 47 ; br boot 48 ; nop 49 ;start1: 50 ; mov #1,r0 51 52 010000 012701 177170 boot: mov #rx2cs,r1 ; put addr of rx2cs into r1 53 010004 012700 100240 mov #mask,r0 ; put bit mask into r0 54 010010 005002 clr R2 ; clear bus addr (dma dest'n addr) 55 010012 012705 000200 mov #wrdcnt,r5 ; put word count (128) into r5 56 010016 012704 000401 mov #401,r4 ; track 1, sector 1 57 010022 012703 177172 $1: mov #rx2db,r3 ; put addr of rx2db in r3 58 59 ; Check that the rxv21 is ready 60 61 010026 030011 $2: bit r0,(r1) ; apply mask to rx2cs 62 010030 001776 beq $2 ; loop until err, xfer-rqst or done 63 010032 100441 bmi quit ; halt if err is set 64 65 ; Initiate a read-sector command 66 67 010034 012711 000407 mov #407,(r1) ; den=dden, unit=0, fn=rd-sector, go 68 010040 030011 $3: bit r0,(r1) ; apply mask to rx2cs 69 010042 001776 beq $3 ; loop until err, xfer-rqst or done 70 010044 100434 bmi quit ; halt if err is set 71 ; Code assumes that xfer-rqst is now set (ignores done) 72 010046 110413 movb r4,(r3) ; write sector number to rx2db 73 010050 000304 swab r4 ; swap track number to bits 0-7 74 010052 030011 $4: bit r0,(r1) ; apply mask to rx2cs 75 010054 001776 beq $4 ; loop until err, xfer-rqst or done 76 ; Code assumes that xfer-rqst (not err or done) is now set 77 010056 110413 movb r4,(r3) ; write track number to rx2db 78 79 ; rxv21 is now reading sector data into its own buffer 80 81 010060 000304 swab r4 ; swap track number to bits 15-8 82 010062 030011 $5: bit r0,(r1) ; apply mask to rx2cs 83 010064 001776 beq $5 ; loop until err, xfer-rqst or done 84 010066 100423 bmi quit ; halt if err is set 85 86 ; Code assumes that xfer-rqst is now set (ignores done) 87 88 ; The sector data is now in rxv21's data buffer. 89 ; Prepare to transfer sector data from rxv21 to ram by dma 90 91 010070 012711 000403 mov #403,(r1) ; den=dden, unit=any, fn=empty-buf, go 92 010074 030011 $6: bit r0,(r1) ; apply mask to rx2cs 93 010076 001776 beq $6 ; loop until err, xfer-rqst or done 94 010100 100416 bmi quit ; halt if err is set 95 ; Code assumes that xfer-rqst is now set (ignores done) 96 010102 010513 mov r5,(r3) ; ld word count into rx2wc via rx2db 97 010104 030011 $7: bit r0,(r1) ; apply mask to rx2cs 98 010106 001776 beq $7 ; loop until err, xfer-rqst or done 99 010110 100412 bmi quit ; halt if err is set 100 ; Code assumes that xfer-rqst is now set (ignores done) 101 010112 010213 mov r2,(r3) ; ld bus addrs into rx2ba via rx2db 102 103 ; Data (256 bytes) is now being copied to ram via dma 104 105 010114 060502 add r5,r2 ; add 128 dec to bus address 106 010116 060502 add r5,r2 ; add 128 dec to bus address 107 010120 122424 cmpb (r4)+,(r4)+ ; increment sector number by 2 108 010122 120427 000007 cmpb r4,#7 ; sectors 1, 3, 5 & 7 will be read 109 010126 003737 ble $2 ; loop back and do next sector 110 010130 012700 000000 mov #0,r0 ; boot device is unit 0 111 010134 005007 clr pc ; go to addr zero 112 113 ; Errors always branch to here. on first error (during 114 ; dden attempt) we change to sden mode and try again. 115 ; Self modifying code here! 116 ; On second error, we halt. 117 118 010136 000005 quit: reset ; reset all i/o devices 119 010140 012700 010000 mov #boot,r0 ; load r0 with start address 120 010144 012701 000400 mov #400,r1 ; setup mask byte 121 010150 006260 000014 asr 14(r0) ; change "mov #wrdcnt,r5" to 64 decimal 122 010154 040160 000036 bic r1,36(r0) ; change "mov #407,(r1)" read-sector cmd to sden 123 010160 040160 000072 bic r1,72(r0) ; change "mov #403,(r1)" empty-buffer cmd to sden 124 010164 012760 000017 000124 mov #17,124(r0) ; change "cmpb r4,#7" last sector to d'15 125 010172 005060 000136 clr 136(r0) ; change "reset" to halt at quit location 126 010176 000700 br boot ; go back and try sden mode 127 128 .end 128