inc/1541.hdr.asm at main · Piddewitt/inc · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
; -------------------------------------------------------------------------------------------------------------- ;
; VIC 1541 - HEADER Block
; -------------------------------------------------------------------------------------------------------------- ;
; The HEADER block is written ONLY once during FORMAT
; -------------------------------------------------------------------------------------------------------------- ;
HDR_SYNC                    = $00               ;       indicates HEADER is coming
HDR_SYNC_VAL                  = $ff             ;       10 ore more 1-bits
HDR_SYNC_COUNT                = $05             ;       NUMSYN
; -------------------------------------------------------------------------------------------------------------- ;


; -------------------------------------------------------------------------------------------------------------- ;
; HDR_BLOCK on Disk is GCR encoded to avoid two subesquent 0-bits and more than 9 subsequent 1-bits (SYNC)
; -------------------------------------------------------------------------------------------------------------- ;
; the original 8 8-bit bytes are
; -------------------------------
;   1 header block ID char
;   1 header checksum
;   1 sector number
;   1 track number
;   2 disk id
;   2 off bytes
; -------------------------------
;   8 BIN bytes ---> 10 GCR bytes
; -------------------------------------------------------------------------------------------------------------- ;
HDR_BLOCK                   = $00               ;
; -------------------------------------------------------------------------------------------------------------- ;
HDR_BLOCK_ID                  = $00             ; flag: this is a HEADER block
HDR_BLOCK_ID_VAL                = HBID_DFLT     ;       normally $08
; -------------------------------------------------------------------------------------------------------------- ;
; checksum: calculated by EORing HDR_BLOCK_TRACK / HDR_BLOCK_SECTOR / HDR_BLOCK_ID
; -------------------------------------------------------------------------------------------------------------- ;
HDR_BLOCK_CRC                 = $01             ;       ensures that a HEADER block was read correctly
; -------------------------------------------------------------------------------------------------------------- ;
; the 1541 has no TRACK_00_DETECTOR (exception: 1541C)
; after powering up and getting a disk command the 1541 reads a SECTOR HEADER to find out where the head is positioned
; -------------------------------------------------------------------------------------------------------------- ;
HDR_BLOCK_SECTOR              = $02             ;       number of this particular SECTOR
HDR_BLOCK_TRACK               = $03             ;       number of this particular TRACK
; -------------------------------------------------------------------------------------------------------------- ;
; checked against Master Dik ID to ensure that Disks are not swapped
; -------------------------------------------------------------------------------------------------------------- ;
HDR_BLOCK_DISK_ID             = $04             ;       from the format CMD (N0:title,cc)
HDR_BLOCK_DISK_ID_CHR2          = $04           ;       -------------------------------^
HDR_BLOCK_DISK_ID_CHR1          = $05           ;       ------------------------------^
; -------------------------------------------------------------------------------------------------------------- ;
; $02 OFF bytes are used to complete $08 bytes
; a multiple of $04 bytes is needed to create a multiple of $05 GCR-bytes
; -------------------------------------------------------------------------------------------------------------- ;
HDR_BLOCK_OFF                 = $06             ;       DOS padding bytes during initial format - never referenced again
HDR_BLOCK_OFF1                  = $06           ;
HDR_BLOCK_OFF2                  = $07           ;
HDR_BLOCK_OFF_VAL                 = $0f         ;
; -------------------------------------------------------------------------------------------------------------- ;


; -------------------------------------------------------------------------------------------------------------- ;
; HEADER gap (GAP1)
; -------------------------------------------------------------------------------------------------------------- ;
HDR_GAP                     = $08               ;       give DOS enough time to set-up for reading the following data block
HDR_GAP_VAL                   = $55             ;
HDR_GAP_COUNT                 = $09             ;       fix GAP1 length
; -------------------------------------------------------------------------------------------------------------- ;