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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 19th Jan 2020, 9:21 pm   #341
john_newcombe
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Default Re: Gemini 80-Bus System

John: Thanks for the above I have the Emulator booting and the disk image works fine. I haven't looked closely but from the size I am thinking that this is a raw image rather than a DMP (or other layout), is this correct? I didn't appreciate that XBeaver could use raw images. The image won't boot the actual machine (using the Gotek) which is a little puzzling, however, I will investigate this further as this could simply be a Gotek config issue.

I have attached links to four photographs of IC 14 in the hope this will help you unravel this particular mystery. Let me know if you need more.

https://glasstty.com/wiki/index.php/...849_IC14_1.jpg
https://glasstty.com/wiki/index.php/...849_IC14_2.jpg
https://glasstty.com/wiki/index.php/...849_IC14_3.jpg
https://glasstty.com/wiki/index.php/...849_IC14_4.jpg
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Old 19th Jan 2020, 11:08 pm   #342
JohnBHanson
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Default Re: Gemini 80-Bus System

Raw is the format that is used if a format option is not specified (eg the default).

Note that some formats (such as compressed .imd) are read only.
Most non raw formats are copied into ram or parsed on initialisation.

A useful trick with raw format is to use a symbolic link in the configuration file. It is then possible to change the symbolic link from a command shell while xbeaver is running to change floppy disk. Do not try this trick with formats that are cached

ps - check the first sector matches your system especially the first two bytes.
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Old 20th Jan 2020, 5:33 am   #343
JohnBHanson
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Default Re: Gemini 80-Bus System

Looks like IC14 is a 74LS51 - thanks John for all the work
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Old 20th Jan 2020, 5:44 am   #344
JohnBHanson
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Default Re: Gemini 80-Bus System

I have checked the signature wanted in simon.rom (offset 0xf031) and it is 6d 47 which is correct for booting the mfb floppy image I posted.
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Old 20th Jan 2020, 9:59 am   #345
john_newcombe
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Default Re: Gemini 80-Bus System

Whilst investigating the Gotek issue, I have started to get confused over the disk layouts. I would appreciate it if you confirm my understanding. i.e.
  • The Gemini Bios interprets GEMDDDS (double sided 35 track disks) as 70 track disks with 10 (512 byte) sectors per track.
  • The Gemini Bios interprets GEMQDDS (double sided 80 track disks) as 80 track disks with 20 (512 byte) sectors per track.
Is this correct?

With GEMDDDS the disk was accessed in the order; Side 0, Trk 0, Sect 0-9 followed by Side 1 Trk 0 Sect 0-9 etc. and the Goteks 'interleaved' file-layout setting seemed to work well...

Code:
#   interleaved:   Interleaved cylinder ordering: c0s0, c0s1, c1s0, c1s1, ...
My confusion is that I cannot get my head around what the physical layout of the GEMQDDS disk is. Looking at the disk image it looks like the sectors are arranged differently with what is presumably CPM stored on sectors 1 to 10 and 21-30 with 11-20 all set to E5. I am wondering if for the purposes of the Gotek whether these need to be shuffled in someway, I certainly can give it a try as it will only take a few lines of code.

In terms of the Gotek, my thinking is that a physical disk has 2 sides, 35/80 cylinders and 10, 512 byte, sectors per track irrespective of how the data is arranged, however, there is a question of how the Gotek accesses the disk image file. Based on the successful GEMDDDS images on the rack system I am assuming it simply accesses them in order.

For completeness, the full range of file layout options are as follows...

Code:
# Optional: Image file track layout. Default is "interleaved".
# Comma-separated values:
#   sequential:    Sequential cylinder ordering: all side 0, then side 1.
#   interleaved:   Interleaved cylinder ordering: c0s0, c0s1, c1s0, c1s1, ...
#   reverse-sideN: Side-N cylinders are ordered from high to low (N=0,1).
#   sides-swapped: Sides 0 and 1 ordering is swapped in the image file.
#   eg. "sequential,reverse-side1"
#file-layout = interleaved
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Old 20th Jan 2020, 10:23 am   #346
JohnBHanson
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Default Re: Gemini 80-Bus System

I think you want interleaved. It actually does not matter what CP/M believes it is actually what is recorded in the file that is important and that is defined by the geometry statement in the .cfg file for the emulator.

QDDS format is 80 tracks, 2 sides and 10 sectors per track. However CP/M does not understand sides and hence the bios re-maps the side count by doubling either the number of sectors of the number of tracks. When the bios drives the hardware it actually drives it as 80 cylinders 2 sides and 10 sectors per track and that is what you need for your floppy setup.

The next issue is the file format should be consistent for the gotek and the xbeaver emulator. This is controlled by the geometry parameter depending on the letter 'S' being present. In raw format without the S option the order of tracks in the file is cyl0side0 cyl0side1, cyl1side0, cyl1side1. Each track consisting of sectors 0..9 in order.

see routine flp_linear_block in floppy.c for details.

So I think you need interleaved set for your file layout - which appears to be also the default.


I hope that helps.
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Old 20th Jan 2020, 10:51 am   #347
john_newcombe
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Default Re: Gemini 80-Bus System

OK, thanks, but what about the bootable floppy image you sent me?

When you helped me construct the DDDS disk image for the Gotek the boot sector was on side 0 sector 0 and cp/m was on the following 16 sectors (if I remember correctly), with all of the sectors stored in the image in order, it all worked nicely with the interleaves setting.

The image we have for QDDS seems to use side 0 sector 0 for the boot sector then sectors 1-10 and sectors 20-30 for the OS, are you saying that I can just ignore that and leave it all to the boot loader/bios to sort this out?
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Old 20th Jan 2020, 11:04 am   #348
JohnBHanson
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Default Re: Gemini 80-Bus System

I enclose a log of the disk activity for booting - this should explain everything....
Attached Files
File Type: zip mfbboot.zip (20.5 KB, 6 views)
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Old 23rd Jan 2020, 2:57 am   #349
john_newcombe
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Default Re: Gemini 80-Bus System

Many thanks, eally appreciated. I will take a look.
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