questions to di and did debugger commands

[Rock'n Roll]

>di r 0
Disk breakpoint mode R-- track 0
>g
DSKLEN: drive 0 motor  on cylinder  0 sel yes rw mfmpos 52533/101344
5295 5555 5255 5555|5495 5555 5555 5555 5495 5555 5555 5555 5295 5555 5255 5555 5295
side 0 dma 2 off 1 word 5555 pt 00002064 len 9CBE bytr 80AA adk 1100 sync 0000
  D0 00009CBE   D1 00000400   D2 00009CBE   D3 00000000
  D4 00000000   D5 00000000   D6 00000000   D7 00000000
  A0 00C04800   A1 00DFF000   A2 00002064   A3 00C04730
  A4 00FEA22A   A5 00000000   A6 00C03AA4   A7 00C04A8C
USP  00C04A8C ISP  00C80000
T=00 S=0 M=0 X=0 N=1 Z=0 V=0 C=0 IMASK=0 STP=0
Prefetch 4e75 (RTS) 43fa (LEA) Chip latch FFFF9CBE
00fea232 4e75                     rts  == $00fea1fc
Next PC: 00fea234
>

1. what triggers this break?
2. what are the numbers and letters stand for?
DSKLEN: drive 0 motor on cylinder 0 sel yes rw mfmpos 52533/101344
5295 5555 5255 5555|5495 5555 5555 5555 5495 5555 5555 5555 5295 5555 5255 5555 5295
side 0 dma 2 off 1 word 5555 pt 00002064 len 9CBE bytr 80AA adk 1100 sync 0000

3. also with

>did 4
Disk logging level 4
>g

...
DSKLEN: drive 0 motor  on cylinder 55 sel yes ro mfmpos 98972/101344
9555 2A51 4A52 5149|1524 492A AA91 5255 1512 A455 24AA 52A9 1149 5111 514A A949 124A
side 0 dma 2 off 15 word 5149 pt 00005DC6 len 98F0 bytr 80A2 adk 1500 sync 4489
SYNC: drive 0 motor  on cylinder 55 sel yes ro mfmpos 5648/101344
AAAA AAAA AAAA 4489|4489 5515 2AA5 5544 AAA9 2AAA AAAA AAAA AAAA AAAA AAAA AAAA AAAA
side 0 dma 2 off 15 word 4489 pt 00005DC6 len 98F0 bytr 8089 adk 1500 sync 4489

4. are there different log level and for what?
did <log level> Enable disk logging.

5. for what is this breakpoint and logging feature helpful? maybe to understand mfm/gcr-encoding?
or disc data structure?

[Toni Wilen]

1. what triggers this break?

DMA start when track is zero. (R=read default, W=write, P=DSKBYTR CPU read)

2. what are the numbers and letters stand for?
DSKLEN: drive 0 motor on cylinder 0 sel yes rw mfmpos 52533/101344
5295 5555 5255 5555|5495 5555 5555 5555 5495 5555 5555 5555 5295 5555 5255 5555 5295
side 0 dma 2 off 1 word 5555 pt 00002064 len 9CBE bytr 80AA adk 1100 sync 0000

Floppy drive state (motor, cylinder, selected, side select) and register contents (DMA pointer, length, DSKBYTR, ADKCON, DSKSYNC)

MFMPOS = current bit position of track/total length. Raw bit stream dump (| = current position)

4. are there different log level and for what?
did <log level> Enable disk logging.

Undefined The bigger the value the more gets dumped.

5. for what is this breakpoint and logging feature helpful? maybe to understand mfm/gcr-encoding?
or disc data structure?

Debug/crack/hack some loader? Log is usually enough to find out where it is called.

[Rock'n Roll]

I try to understand:

first line:
DSKLEN: - info label, like SYNC:
drive 0 - ok, it's df0:
motor on - motor state
cylinder 0 - track 0, side 0 (info)
sel yes rw - ?
mfmpos 52533/101344 - ok, current bit position

total length: 101344?
1 track = 11*512 Bytes*8= 45056 Bits
MFM=11*(2*(64Byte+512Byte))*8=101376 Bits

second line:
data - 17 words, mfm data (but not synchronized)
data are not from the beginning of a track?
the current position stands anywhere? like here: 52533?
(Then a breakpoint for a certain mfmpos would be good?
To analyze mfm-data from beginning of a track)

| = current position - ok, from the raw bit stream dump

third line:
side 0 - ok, see cylinder 0
dma 2 - ? dma is always 2?
off 1 - ? off with different numbers from 1 to 13?
word 5555 - ok, current value
pt 00002064 - DSK pointer ($dff020,22 DSKPTH, DSKPTL)
len 9CBE - ok, length ($dff024 DSKLEN)
bytr 80AA - ok, DSKBYTR ($dff01A DSKBYTR)
adk 1100 - ok, ADKCON ($dff010 ADKCONR)
sync 0000 - ok, DSKSYNC ($dff07E DSKSYNC)

SYNC: drive 0 motor on cylinder 69 sel yes rw mfmpos 5648/101344
AAAA AAAA AAAA 4489|4489 5545 2AA5 552A AAA9 2AAA AAAA AAAA AAAA AAAA AAAA AAAA AAAA
side 0 dma 2 off 0 word 4489 pt 00070000 len 9F40 bytr 8044 adk 1500 sync 4489

What means SYNC?
It's this preamble and syncword? AAAA AAAA 4489|4489
But why there are three times AAAA AAAA AAAA and not only 2 times?

[Toni Wilen]

Originally Posted by Rock'n Roll

o)
sel yes rw - ?

Drive selected (yes) or not selected (no). (SEL0-SEL3 bits)

total length: 101344?

Total number of bits in this track.

1 track = 11*512 Bytes*8= 45056 Bits
MFM=11*(2*(64Byte+512Byte))*8=101376 Bits

It is theoretical max bits that Amiga can write. It is not logical floppy format size.

PAL: 3546895 / (7 * 5)
NTSC: 3579545 / (7 * 5)

(7 = clocks per bit, 5 = 5 revs/second)

dma 2 - ? dma is always 2?

DMA state.
0 = off.
1 = first DSKLEN write only done.
2 = read DMA active.
3 = write DMA active.

off 1 - ? off with different numbers from 1 to 13?

Current bit position in current loaded word. (Not very useful)

What means SYNC?

It means debug log message was caused by DSKSYNC match. Another possibility is DSKLEN write (DMA started).

It's this preamble and syncword? AAAA AAAA 4489|4489
But why there are three times AAAA AAAA AAAA and not only 2 times?

It always shows last 4 words. Nothing to do with sync.

[Rock'n Roll]

thank you for the information.

What I'm missing at the end is an example of what it could be useful.
So, how I have to interpret the raw bit stream data?

I see no connection between the data on an adf file and the raw bit stream.
I also don't get a connecetion between the current bitposition 98972 and to the hex data, e.g. of an adf file.

[Toni Wilen]

Learn how Amiga MFM encoding works

WinUAE does not care or need to know. Raw bit stream is DMA'd to memory. MFM decoding is done by Amiga side software (trackdisk.device or game/demo trackloader).

In theory UAE could decode it but it would return garbage if format is not standard AmigaDOS.