; Dissassembly of CP/M 2.2 boot sector
; (track 0, side 0, sector &41) on side 4 of CPC6128 system discs
; Boot sector for CP/M 2.2
;
; Entry values as defined by AMSDOS ROM:
; 
; Note actual values could change, but the meaning will be the same:
; 
; BC = &C17F - C/PM BIOS calls in AMSDOS ROM
; SP = &AD33
; DE = &C163 -> interrupt handler
; HL = &100 - start address of boot sector

;; copy CPM BIOS into RAM from ROM
0100 60        ld      h,b
0101 69        ld      l,c
0102 110005    ld      de,&0500
0105 013300    ld      bc,&0033
0108 edb0      ldir    

;; read track 0, side 0, sector &42 to &300 in RAM
010a 0e42      ld      c,&42
010c 110000    ld      de,&0000
010f 210003    ld      hl,&0300
0112 cd89be    call    &be89 ; BIOS READ SECTOR
0115 3006      jr      nc,&011d			;; NC = load fail, C = load succeeded

0117 cd5001    call    &0150			;; check valid, perform expansion buffer, configure cpm
011a c30305    jp      &0503			;; WBOOT

011d cd5902    call    &0259 ;; display inline message
0120 
defb 13,10,"Failed to load the configuration sector",13,10,10,"$"
014d c30305    jp      &0503			;; WBOOT

0150 cd5902    call    &0259 ;; display inline message
0153 
defb 4,2,"$"

0156 2a0003    ld      hl,(&0300)		;; some kind of check 
										;; HL = &1235
0159 11cbed    ld      de,&edcb			
015c 19        add     hl,de
015d 7c        ld      a,h
015e b5        or      l
015f 2826      jr      z,&0187

0161 cd5902    call    &0259 ;; display inline message
0164 
defb 13,10,"Illegal configuration sector",13,10,10,"$"
0186 c9        ret    
 
0187 2a0203    ld      hl,(&0302)
018a 223d02    ld      (&023d),hl		;; motor on timeout in 20 millisecond units
018d 2a0403    ld      hl,(&0304)
0190 223f02    ld      (&023f),hl		;; motor off timeout in 20 millisecond unots
0193 3a0603    ld      a,(&0306)
0196 324302    ld      (&0243),a		;; step rate in 1 millisecond units

0199 213d02    ld      hl,&023d
019c cd83be    call    &be83			;; BIOS_SETUP_DISC

019f 3a0703    ld      a,(&0307)		
01a2 320300    ld      (&0003),a		;; IOBYTE

01a5 3a0803    ld      a,(&0308)
01a8 cd80be    call    &be80			;; BIOS_SET_MESSAGE
01ab 3a0903    ld      a,(&0309)
01ae cd9ebe    call    &be9e			;; SET_REG_SAVE
01b1 210a03    ld      hl,&030a
01b4 cda1be    call    &bea1			;; SET_SIO

01b7 216403    ld      hl,&0364
01ba cd5f02    call    &025f ; display message terminated with $

;;......?
01bd 7e        ld      a,(hl)
01be 23        inc     hl
01bf b7        or      a
01c0 280c      jr      z,&01ce
01c2 47        ld      b,a
01c3 4e        ld      c,(hl)
01c4 23        inc     hl
01c5 e5        push    hl
01c6 c5        push    bc
01c7 cd0f05    call    &050f			;; LIST
01ca c1        pop     bc
01cb e1        pop     hl
01cc 10f5      djnz    &01c3

01ce eb        ex      de,hl
01cf 2127bb    ld      hl,&bb27			;; KM SET TRANSLATE
01d2 cd4602    call    &0246
01d5 212dbb    ld      hl,&bb2d			;; KM SET SHIFT
01d8 cd4602    call    &0246
01db 2133bb    ld      hl,&bb33			;; KM SET CONTROL
01de cd4602    call    &0246
01e1 eb        ex      de,hl
01e2 7e        ld      a,(hl)
01e3 23        inc     hl
01e4 b7        or      a
01e5 2850      jr      z,&0237
01e7 57        ld      d,a
01e8 46        ld      b,(hl)
01e9 23        inc     hl
01ea 4e        ld      c,(hl)
01eb 23        inc     hl
01ec e5        push    hl
01ed d5        push    de
01ee c5        push    bc
01ef cd0fbb    call    &bb0f			;; KM SET EXPAND
01f2 c1        pop     bc
01f3 d1        pop     de
01f4 e1        pop     hl
01f5 383a      jr      c,&0231

01f7 cd5902    call    &0259 ;; display inline message			

01fa 
defb 13,10,"Expansion buffer full or illegal token specified",13,10,10,"$"
0230 c9        ret     

0231 0600      ld      b,&00
0233 09        add     hl,bc
0234 15        dec     d
0235 20b1      jr      nz,&01e8

0237 3a1603    ld      a,(&0316)			
023a c3a4be    jp      &bea4				;; SET_CMND_BUFFER 

;; params for BIOS SETUP DISC
023d 
defw 0								;; motor on timeout
defw 0								;; motor off timeout
defw &af							;; write current off time in 10 microsecond units
defb &1e							;; head settle time in 1 millisecond units
defb &00							;; step rate time in 1 millisecond units
defb &1								;; head unload delay (as per uPD765A SPECIFY command)
defb &3								;; bits 7..1: head load delay, bit 0: non DMA mode

;; DE points to some data
;;
;; 1: count
;; then pairs of values
;; B = first value (new token or character), A = second value (key number)
0246 1A		   ld      a,(de)
0247 4f        ld      c,a
0248 13        inc     de
0249 b7        or      a
024a c8        ret     z

024b 1a        ld      a,(de)
024c 47        ld      b,a
024d 13        inc     de
024e 1a        ld      a,(de)
024f 13        inc     de
0250 e5        push    hl
0251 cd6c02    call    &026c		;; effectively: CALL (HL) 
0254 e1        pop     hl
0255 0d        dec     c
0256 20f3      jr      nz,&024b
0258 c9        ret     

;; display message
;;
;; message follows CALL, and execution returns to the instruction after the end
;; of the message
0259 e3        ex      (sp),hl
;; HL = address of message
025a cd5f02    call    &025f ; display message terminated with $
;; HL = byte after end of message
025d e3        ex      (sp),hl
025e c9        ret     

;; display message terminated with '$' char
025f 7e        ld      a,(hl)
0260 23        inc     hl
0261 fe24      cp      '$'		;; end of string marker
0263 c8        ret     z

0264 4f        ld      c,a
0265 e5        push    hl
0266 cd0c05    call    &050c	;; CONOUT
0269 e1        pop     hl
026a 18f3      jr      &025f ; display message terminated with $

026c e9        jp      (hl)

;; rest of sector is filled with &cf
rept &300-&26d
defb &cf
endm