Hard sector format

HxC Floppy emulator support for all others computers...
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Jeff
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Re: Hard sector format

Post by Jeff » Mon Oct 30, 2017 11:39 pm

Can we put here the exact supposed layout/format ?
I mean something like this (for example):

[Preamble Byte 0x00 * 12][ID Mark 0xAA * 2] [Track Number][Side Number][Data Sector (256][CRC Low][CRC High][GAP 0xFF * 16]

snhirsch
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Re: Hard sector format

Post by snhirsch » Tue Oct 31, 2017 3:44 pm

That's a good idea. I'll work it up and try to post this evening. Re: Trailing gap. I do not believe this concept is relevant for hard-sector formats since the controller is expected to re-sync after each index pulse.

snhirsch
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Re: Hard sector format

Post by snhirsch » Sat Nov 04, 2017 3:43 pm

Here is a compilation of everything known about the Northstar DD format:

Code: Select all

Northstar DD floppy format

10-sectors per track x 35 tracks per side
MFM encoding

Single and double-sided formats are supported

---

Data Layout

[Sector index (rising edge)]
[96 us delay]
[Preamble = 33 Bytes of 0]
[Sync 0xFB 1-byte]
[Track-Sector 1-byte (see below)]
[Data 512-bytes]
[Checksum 1-byte (see below)]

There is no formal padding at the end of the sector. In a hard-sector
format the diskette controller is expected to re-sync on the next
index hole.

---

Track-Sector Byte Detail

  Bits 0-3 = Sector (0..9)

  Physical Order from rotational index: 0 2 4 6 8 1 3 5 7 9

  Bits 4-7 are related to the track.

On side 0 of a diskette, the value in bits 4-7 cycles through the
sequence: 0x0 0x4 0x8 0xC as track advances. In other words,
tracks 0, 4, 8, 12, 16, 20, 24, 28, 32 have a value of '0x0' in the
upper four bits.  Tracks 1, 5, 9, 13, 17, 21, 25, 29, 33 have a value
of 0x4 in the upper bits, etc.

On side 1 of a double-sided diskette, the value in bits 4-7 cycles
through the sequence: 0x1, 0x5, 0x9, 0xD as we advance inward from the
outermost track. This amounts to the same pattern shown above, but
with bit 4 set to denote the second side of the diskette.

---

Checksum Byte Detail

The checksum algorithm works as follows:

// Sector data
unsigned char data[512];

unsigned char csum = 0;
for (int i=0; i<512; i++) {
  csum = csum ^ data[i];
  csum = (csum << 1)|(csum >> 7);
}

// Resulting value is written to diskette as the checksum byte.

---

Logical data organization on double-sided diskette

Data is written in a serpentine order:

Side 0:  Track 0..34
Side 1:  Track 34..0

---

NOTE:

The Northstar technical documentation has a discrepancy between
figures and text.  Figures 3-4 and 3-5 show the layout for DD MFM
diskettes with 512-byte sectors.  The text references an older SD FM
format with 256-byte sectors.

The document you are reading now is intended to cover the DD MFM
512-byte format.

snhirsch
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Re: Hard sector format

Post by snhirsch » Mon Nov 06, 2017 6:51 pm

Hi, Jeff. You should have what you need now (see previous message).

Jeff
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Re: Hard sector format

Post by Jeff » Mon Nov 06, 2017 10:06 pm

snhirsch wrote:
Mon Nov 06, 2017 6:51 pm
Hi, Jeff. You should have what you need now (see previous message).
This seems perfect.
I presume that the sync word have no missing clock ?

snhirsch
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Re: Hard sector format

Post by snhirsch » Mon Nov 06, 2017 10:24 pm

Good question about the missing clock. I think we may have to settle that by experimentation. Neither the FC-5025 nor Catweasel code cared about this, since they were simply counting bit cells. Let's assume it's not missing for the first try.

This would be simpler if the Kryoflux people were willing to support hard-sector formats. They seem convinced that a special drive mechanism is required, but that's simply not correct. There were some older 8" drives with on-board data separators for hard sector formats, but that capability is not required to read flux transitions.

snhirsch
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Re: Hard sector format

Post by snhirsch » Fri Dec 01, 2017 5:15 pm

Hi, Jeff.

Has there been any progress on hard sector support? FYI: I have been contacted by the Kryoflux folks and asked to supply them with example media for analysis. Maybe we'll get lucky and they will add support.

Jeff
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Re: Hard sector format

Post by Jeff » Tue Dec 05, 2017 11:32 pm

snhirsch wrote:
Fri Dec 01, 2017 5:15 pm
Hi, Jeff.

Has there been any progress on hard sector support? FYI: I have been contacted by the Kryoflux folks and asked to supply them with example media for analysis. Maybe we'll get lucky and they will add support.
still busy with the stm32 firmware. :(

Jeff
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Re: Hard sector format

Post by Jeff » Mon Dec 18, 2017 9:13 am

snhirsch wrote:
Fri Dec 01, 2017 5:15 pm
Hi, Jeff.

Has there been any progress on hard sector support? FYI: I have been contacted by the Kryoflux folks and asked to supply them with example media for analysis. Maybe we'll get lucky and they will add support.
https://forum.kryoflux.com/viewtopic.php?f=3&p=12415
[...]
We might be also looking into supporting "real" hard-sectored formats (where the sector index information was actually used), but reliable/low-level information is pretty scarce on those, and we simply do not have any such disk.
@snhirsch
Do you you think that you will able to "tweak"/make changes into the track encoder once i will release it ?
will be faster since i don't have this machine nor any disk to make working at the first release...

Dutchacorn
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Re: Hard sector format

Post by Dutchacorn » Sun Apr 29, 2018 10:15 pm

Hi Jeff,

Also very interested in any progress on supporting hard sector format disk emulation! I have the SD card emulator from Lotharek.

I have an Exidy Sorcerer with 40x10x512 hard sectored disk access trough a Vista S-100 bus FDC. It came with a few dozen hard sectored disks but many of them are disintegrating and/or failing. It would be great to 1) archive the software on these disks and 2) be able to keep using original hardware. It is basically CP/M but some of this software is specific to the Sorcerer.

New hard sectored floppy disks are impossible to get. There have been some initiatives creating a device to punch in the extra holes needed for hard sectoring using soft sectored disks, but nothing available currently. Another development is separate logic to create the extra pulses (see here). This only works with "modern" floppy drives (perhaps also with an HxC?).

I could help sending a hard sectored floppy disk to you if that would help...

snhirsch
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Joined: Tue Dec 08, 2015 1:42 am

Re: Hard sector format

Post by snhirsch » Mon Apr 30, 2018 12:20 am

Join the club of folks waiting for hard-sector support :-). FWIW: The sector pulse generator does NOT work with HxC. That was one of the first things I tried. The Kryoflux folks recently added support for capture of RAW hard-sector images. This does not help with data extraction, but does provide complete details on the flux layout. I've captured images from Heath and Northstar hard-sector diskettes and sent them to Jeff.

Dutchacorn
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Joined: Sun Apr 29, 2018 9:53 pm

Re: Hard sector format

Post by Dutchacorn » Mon Apr 30, 2018 10:28 pm

snhirsch wrote:
Mon Apr 30, 2018 12:20 am
Join the club of folks waiting for hard-sector support :-). FWIW: The sector pulse generator does NOT work with HxC. That was one of the first things I tried. The Kryoflux folks recently added support for capture of RAW hard-sector images. This does not help with data extraction, but does provide complete details on the flux layout. I've captured images from Heath and Northstar hard-sector diskettes and sent them to Jeff.
Thanks for the input on the combination of pulse generator and HxC! It would be great if support would be added. The number of Sorcerers is declining and so is the availability of software for these machines, would be nice if some of it could be saved. :D

snhirsch
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Re: Hard sector format

Post by snhirsch » Mon Apr 30, 2018 10:50 pm

@snhirsch
Do you you think that you will able to "tweak"/make changes into the track encoder once i will release it ?
will be faster since i don't have this machine nor any disk to make working at the first release...
I never saw this message. I'm a reasonably competent software engineer and would be glad to help in any way I can. At one point I checked out all the source code for Floppy Emulator, but without a high-level overview it was really difficult to make sense of. With some guidance I'd be happy to dive in further.

Jeff
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Re: Hard sector format

Post by Jeff » Tue May 01, 2018 2:48 pm

snhirsch wrote:
Mon Apr 30, 2018 10:50 pm
@snhirsch
Do you you think that you will able to "tweak"/make changes into the track encoder once i will release it ?
will be faster since i don't have this machine nor any disk to make working at the first release...
I never saw this message. I'm a reasonably competent software engineer and would be glad to help in any way I can. At one point I checked out all the source code for Floppy Emulator, but without a high-level overview it was really difficult to make sense of. With some guidance I'd be happy to dive in further.
well i need to fix the kf stream importer and then you should be able to emulate the drive in read-only mode from the stream.

snhirsch
Posts: 160
Joined: Tue Dec 08, 2015 1:42 am

Re: Hard sector format

Post by snhirsch » Tue May 01, 2018 4:47 pm

Good to hear! Hopefully that will be ready soon and full R/W support not too far behind :-)

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