;; Elite - Gold Edition ;; ;; Firebird '86 3b00 1600 ld d,$00 3b02 cd463c call $3c46 ;; start cassette motor ;; select text window 1 3b05 3e01 ld a,$01 3b07 cdb4bb call $bbb4 ;; firmware function: txt str select ;; select pen 2 for displaying text 3b0a 3e01 ld a,$01 3b0c cd90bb call $bb90 ;; firmware function: txt set pen 3b0f cda53c call $3ca5 ;; display "Searching xx" ;; sync byte 3b12 3e0f ld a,$0f 3b14 32305a ld ($5a30),a ;; block additional data count 3b17 3e08 ld a,$08 3b19 32465b ld ($5b46),a ;;--------------------------------------------- 3b1c cdfc3b call $3bfc ;; delay and calc block size 3b1f cd903b call $3b90 ;; read block 3b22 3a325b ld a,($5b32) ;; block number 3b25 ba cp d ;; matches loaded block number? 3b26 2805 jr z,$3b2d ;; block number doesn't match 3b28 cd763c call $3c76 ;; display "Block ? xx" ;; restart 3b2b 18e5 jr $3b12 ;;------------------------------------ 3b2d cd073c call $3c07 ;; checksum data 3b30 be cp (hl) ;; checksum matches? 3b31 2805 jr z,$3b38 3b33 cd763c call $3c76 ;; display "Block ? xx" ;; restart 3b36 18da jr $3b12 ; (-$26) ;;------------------------------------- ;; checksum byte defines next sync byte value 3b38 e67f and $7f 3b3a f608 or $08 3b3c 32305a ld ($5a30),a 3b3f 181c jr $3b5d ; display loading 3b41 cdfc3b call $3bfc ;; delay and calc block size 3b44 cd903b call $3b90 ;; read block 3b47 3a325b ld a,($5b32) ;; block number 3b4a ba cp d ;; same as block number read? 3b4b 2805 jr z,$3b52 ; 3b4d cd763c call $3c76 ;; display "Block ? xx" 3b50 18ef jr $3b41 ; restart ;;------------------------------------------- ;; valid block loaded 3b52 cd073c call $3c07 ;; checksum data 3b55 be cp (hl) ;; matches stored checksum? 3b56 2805 jr z,$3b5d ; 3b58 cd763c call $3c76 ;; display "Block ? xx" 3b5b 18e4 jr $3b41 ;; restart ;;------------------------------------------- ;; checksum matches 3b5d cd7b3b call $3b7b ;; copy loaded data to correct location 3b60 cd4e3c call $3c4e ;; display "Loading xx" 3b63 21355b ld hl,$5b35 3b66 7e ld a,(hl) 3b67 23 inc hl 3b68 3d dec a 3b69 20fc jr nz,$3b67 ; (-$04) 3b6b 23 inc hl 3b6c 23 inc hl 3b6d 23 inc hl 3b6e 23 inc hl 3b6f 7e ld a,(hl) 3b70 2b dec hl 3b71 2b dec hl 3b72 2b dec hl 3b73 e607 and $07 3b75 3c inc a 3b76 32465b ld ($5b46),a 3b79 14 inc d 3b7a e9 jp (hl) ;;----------------------------------------------------------------------- ;; copy loaded data to correct location 3b7b d5 push de 3b7c e5 push hl 3b7d ed5b335b ld de,($5b33) ;; destination for block 3b81 21325a ld hl,$5a32 ;; address block has been loaded to 3b84 010001 ld bc,$0100 ;; length of block 3b87 edb0 ldir 3b89 e1 pop hl 3b8a d1 pop de 3b8b fde1 pop iy 3b8d fde5 push iy 3b8f c9 ret ;;-------------------------------------------------------- ;; data structure: ;; ;; offset length description ;; 0 256 data ;; 256 1 block id ;; 257 2 destination address ;; .. extra bytes unknown ;; ;; Each block has the following composition: ;; ;; - the pilot/leader is composed of a byte stream ;; ;; - there must be at least 5 pilot bytes ;; for the loader to sync to the pilot ;; ;; additional pilot bytes are read but not required ;; ;; - following the pilot byte there is sync byte 1 ;; ;; - following sync byte 1 there is sync byte 2 ;; ;; - following sync byte 2 there is the data ;; ;; (additional bytes ARE read; the purpose of these is to be discovered) ;; ;; in this loader: ;; sync_byte2 = ($5a30) ;; pilot = sync_byte2 ;; sync_byte1 = NOT sync_byte2 3b90 f3 di 3b91 c5 push bc 3b92 d5 push de 3b93 e5 push hl 3b94 3a305a ld a,($5a30) ;; sync byte 2 3b97 2f cpl 3b98 67 ld h,a ;; sync byte 1 3b99 2f cpl 3b9a 6f ld l,a ;; sync byte 2 ;; sync_byte_2 = NOT sync_byte_1 3b9b 57 ld d,a 3b9c cdd33b call $3bd3 ;; read a byte 3b9f ba cp d ;; matches pilot/leader byte 3ba0 2805 jr z,$3ba7 3ba2 cdef3b call $3bef ;; wait for cassette data input to change state 3ba5 18f5 jr $3b9c ; (-$0b) 3ba7 1e04 ld e,$04 3ba9 cdd33b call $3bd3 ;; read a byte 3bac ba cp d 3bad 20ed jr nz,$3b9c ; (-$13) 3baf 1d dec e 3bb0 20f7 jr nz,$3ba9 ; (-$09) ;; keep looping while pilot byte is found 3bb2 cdd33b call $3bd3 ;; read a byte 3bb5 ba cp d 3bb6 28fa jr z,$3bb2 ;; keep looping while pilot byte is read ;; found sync byte 1? 3bb8 bc cp h 3bb9 20e1 jr nz,$3b9c ;; no, try again ;; read sync byte 2 3bbb cdd33b call $3bd3 ;; read a byte 3bbe bd cp l ;; sync byte 2? 3bbf 20db jr nz,$3b9c ;; no try again ;; read data block 3bc1 21325a ld hl,$5a32 3bc4 cdd33b call $3bd3 ;; read a byte 3bc7 77 ld (hl),a ;; store byte 3bc8 23 inc hl ;; increment pointer 3bc9 0b dec bc ;; decrement count 3bca 78 ld a,b 3bcb b1 or c 3bcc 20f6 jr nz,$3bc4 ;; repeat for all bytes 3bce e1 pop hl 3bcf d1 pop de 3bd0 c1 pop bc 3bd1 fb ei 3bd2 c9 ret ;;------------------------------------------------------ ;; read a byte 3bd3 c5 push bc 3bd4 d5 push de 3bd5 06f5 ld b,$f5 ;; PPI port B input ;; (includes cassette input data) 3bd7 1601 ld d,$01 3bd9 1e00 ld e,$00 ;; reset duration count 3bdb ed48 in c,(c) ;; get initial state 3bdd 1c inc e ;; increment duration 3bde ed78 in a,(c) ;; get current state 3be0 a9 xor c ;; any bit that has changed state will be 1 ;; any bit that has not changed state will be 0 3be1 f2dd3b jp p,$3bdd ;; has bit 7 (cassette data input) changed? 3be4 3e3f ld a,$3f ;; bit timing constant 3be6 bb cp e ;; no carry = greater than equal comparison = bit 0 ;; carry = less = bit 1 3be7 cb12 rl d ;; shift bit into data 3be9 30ee jr nc,$3bd9 ;; found 3beb 7a ld a,d 3bec d1 pop de 3bed c1 pop bc 3bee c9 ret ;;------------------------------------------------------------------- ;; wait for cassette input to change state 3bef c5 push bc 3bf0 06f5 ld b,$f5 ;; PPI port B input ;; (includes cassette input data) 3bf2 ed48 in c,(c) ;; get initial state 3bf4 ed78 in a,(c) ;; get current state 3bf6 a9 xor c ;; if a bit has changed, it will be 1, if a bit hasn't changed ;; it will be 0 3bf7 f2f43b jp p,$3bf4 ;; has bit 7 (cassette data input) changed? 3bfa c1 pop bc 3bfb c9 ret ;;------------------------------------------------------------------------- ;; delay & calc block size ;; block has 256 bytes of data, a 1 byte checksum 3bfc 3a465b ld a,($5b46) 3bff 010801 ld bc,$0108 3c02 03 inc bc 3c03 3d dec a 3c04 20fc jr nz,$3c02 ; (-$04) 3c06 c9 ret ;;------------------------------------------------------------------------- ;; checksum block data 3c07 d5 push de 3c08 cdfc3b call $3bfc ;; delay and calc block size 3c0b 0b dec bc 3c0c 21325a ld hl,$5a32 3c0f ae xor (hl) 3c10 5f ld e,a 3c11 23 inc hl 3c12 0b dec bc 3c13 78 ld a,b 3c14 b1 or c 3c15 7b ld a,e 3c16 20f7 jr nz,$3c0f ; (-$09) 3c18 d1 pop de 3c19 c9 ret ;;--------------------------------------------------- ;; display current block number and increment block 3c1a 21325b ld hl,$5b32 ;; block number 3c1d 7e ld a,(hl) 3c1e 34 inc (hl) ;; display a number as hex (A = number) 3c1f f5 push af 3c20 07 rlca 3c21 07 rlca 3c22 07 rlca 3c23 07 rlca 3c24 cd283c call $3c28 3c27 f1 pop af ;; display hex digit 3c28 e60f and $0f ; isolate lower nibble 3c2a f630 or $30 ; convert to ASCII 3c2c fe3a cp $3a 3c2e 3802 jr c,$3c32 ; (+$02) 3c30 c607 add a,$07 3c32 cd5abb call $bb5a ; firmware function: txt output 3c35 c9 ret ;;---------------------------------------------------- 3c36 c5 push bc 3c37 d5 push de 3c38 57 ld d,a 3c39 4f ld c,a 3c3a 47 ld b,a 3c3b 10fe djnz $3c3b ; (-$02) 3c3d 0d dec c 3c3e 20fa jr nz,$3c3a ; (-$06) 3c40 15 dec d 3c41 20f6 jr nz,$3c39 ; (-$0a) 3c43 d1 pop de 3c44 c1 pop bc 3c45 c9 ret ;;---------------------------------------------------- ;; start cassette motor 3c46 c5 push bc 3c47 0110f6 ld bc,$f610 3c4a ed49 out (c),c 3c4c c1 pop bc 3c4d c9 ret ;;----------------------------------------------------- ;; display "Loading xx" 3c4e e5 push hl 3c4f d5 push de ;; select text window 2 3c50 3e02 ld a,$02 3c52 cdb4bb call $bbb4 ;; firmware function: txt str select ;; clear text window 2 3c55 cd6cbb call $bb6c ;; firmware function: txt clear window ;; select text window 1 3c58 3e01 ld a,$01 3c5a cdb4bb call $bbb4 ;; firmware function: txt str select ;; select pen 1 for displaying text 3c5d 3e01 ld a,$01 3c5f cd90bb call $bb90 ;; firmware function: txt set pen 3c62 cdce3c call $3cce ;; display string following this ;; function call defb &0d,"Loading ",0 3c71 d1 pop de 3c72 e1 pop hl 3c73 c31a3c jp $3c1a ;; display current block number and increment ;;----------------------------------------------------- ;; display "Block ? xx" 3c76 e5 push hl 3c77 5f ld e,a 3c78 d5 push de ;; select text window 1 3c79 3e01 ld a,$01 3c7b cdb4bb call $bbb4 ;; firmware function: txt str select ;; set pen 3 for displaying text 3c7e 3e03 ld a,$03 3c80 cd90bb call $bb90 ;; firmware function: txt set pen 3c83 cdce3c call $3cce ;; display string following this ;; function call defb &0d,"Block ? ",0 3c92 cd1a3c call $3c1a ;; display current block number and increment ;; select text window 2 3c95 3e02 ld a,$02 3c97 cdb4bb call $bbb4 ;; firmware function: txt str select ;; select pen 3 for displaying text 3c9a 3e03 ld a,$03 3c9c cd90bb call $bb90 ;; firmware function: txt set pen 3c9f d1 pop de 3ca0 7b ld a,e 3ca1 ba cp d 3ca2 3016 jr nc,$3cba ; (+$16) 3ca4 e1 pop hl ;;------------------------------------------------------------- ;; display "Searching xx" 3ca5 e5 push hl 3ca6 cdce3c call $3cce ;; display string following this ;; function call defb &0d,"Searching ",0 3cb5 7a ld a,d 3cb6 e1 pop hl 3cb7 c31f3c jp $3c1f ;; display hex number in register A ;;------------------------------------------------------------- ;; display "Rewind to xx" 3cba cdce3c call $3cce ;; display string following this ;; function call defb &0d,"Rewind to ",0 3cc9 7a ld a,d 3cca e1 pop hl 3ccb c31f3c jp $3c1f ;;----------------------------------------------------------------------- ;; display null terminated string ;; the string location is on the stack 3cce e1 pop hl 3ccf 7e ld a,(hl) ;; read ASCII character 3cd0 23 inc hl ;; increment pointer 3cd1 fe00 cp $00 ;; end of string marker? 3cd3 c45abb call nz,$bb5a ;; firmware function: txt output 3cd6 20f7 jr nz,$3ccf ;; 3cd8 e5 push hl 3cd9 c9 ret ;;--------------------------------------------------------------- ;; end of dissassembly