Xerox 820 disk format

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stefano
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Xerox 820 disk format

Post by stefano »

I unsuccesfully tried to build a valid disk image for the Xerox 820.
I'm 90% sure the definition is correct:

static disc_spec x820_spec = {
.name = "Xerox820",
.disk_mode = FM250,
.sectors_per_track = 18,
.tracks = 40,
.sides = 1,
.sector_size = 128,
.gap3_length = 0x2a,
.filler_byte = 0xe5,
.boottracks = 3,
.directory_entries = 32,
.extent_size = 1024,
.first_sector_offset = 1,
.has_skew = 1,
.skew_tab = { 0,5,10,15,2,7,12,17,4,9,14,1,6,11,16,3,8,13 }
};

For some reason MAME doesn't like the created files, so I'm not pulling this table in appmake until we get it tested in some way.
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dom
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Re: Xerox 820 disk format

Post by dom »

Do you need has byte size extent as well?
stefano
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Re: Xerox 820 disk format

Post by stefano »

Wow you probably spotted the problem!
stefano
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Re: Xerox 820 disk format

Post by stefano »

It worked !
x820_tris.png
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jorgegv
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Re: Xerox 820 disk format

Post by jorgegv »

I'm always amazed at the density of platform-specific knowledge that is stored in this forum and its users :-)

Surgically exact, pinhead specific knowledge :D
stefano
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Re: Xerox 820 disk format

Post by stefano »

and the 10% of the definition was not correct 🤣
but technically it was not wrong, just not complete
stefano
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Re: Xerox 820 disk format

Post by stefano »

I think it was me pulling the code to get the x820 booting again after the big rework the mame team did on the floppy disk formats.
I suspect the BigBoard could be booting too *if* a single side 40trk boot image existed.
All the disk images available are for 8" drives or 5" HD drives formatted with 77trk, 26 sectors
stefano
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Re: Xerox 820 disk format

Post by stefano »

I can confirm the statement above.
The current MAME emulation is slightly messy but allows the Xerox820 (first version) to be configured with BIOS mods allowing to boot 77trk disks, including the BigBoard CP/M.
The emulation engine in MAME shares most of the code between x820, bigboard,mk82 and mk83, showing they were VERY close relatives.

I'll add the 8" floppy format
bb1_cpm_8in.png
To access to 8" floppy disks with MAME:
- start MAME with the "x820" machine type
- change the machine BIOS to "MICROCode SmartROM v2.3"
- enter to "Slot Devices" and change the floppy disk types from "sa400l" to "sa800"

Now (not before!) enter in File Manager and open the floppy disk image.
Valid boot disks in 8" format are in the Dunfield website, the suggested BIOS will properly boot most of the BigBoard or Xerox 820 (first release) disk images:
http://dunfield.classiccmp.org/img42841/system.htm

Assigning a wrong floopy disk format before changing the disk drive type and resetting the system could crash MAME.
Be patient, and try again :)
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stefano
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Re: Xerox 820 disk format

Post by stefano »

+sound library for the Xerox 820ii

This one was difficult to test because I can't boot the 820ii, I worked around the problem borrowing the sound emulation and using it on the x820.
Not a standard way to play sounds really, OUTs to 2 different addresses to toggle the speaker high/low, the written data doesn't matter.
I think I found something similar already, but I can't remember what it was (perhaps it was an S100 board).
stefano
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Re: Xerox 820 disk format

Post by stefano »

The display.
I haven't checked the earlied X820 model yet, but I suppose that the paging logic was the same.

Code: Select all

; (F293) crtoff - turn crt ram off.

crtoff:
	di            ; lock pio access
	in a,($1C)    ; syspio: get pio status

crtof1: 
	res 7,a       ; reset crt bank enable
	ei            ; unlock pio access

crton1:
	out ($1C),a   ; syspio
	ret


;(F29C) crt on - turn crt ram on.

crton:
	di            ; lock time-out interrupt
	in a,($1C)    ; syspio: get pio status
	set 7,a       ; enable bank
	jr crton1


;(F2A3) crt ldir - block move from/to crt memory.

; Entry:
; HL Source address
; DE Destination address
; BC Number of bytes to move
; A = 0 - Move crt ram to crt ram
; A < 0 - Move sys ram to crt ram
; A > 0 - Move crt ram to sys ram

The video memory will get paged in at $3000, 80x24 characters.
The Xerox820ii should have also a 4x4 "business graphics" (=blocky :D ) mode.

Dom, probably I asked already but, is there existing code I could copy from ?
Just for fun, do you prefer to play with it yourself ?
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dom
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Re: Xerox 820 disk format

Post by dom »

Send me the ROMs and bootdisc and I’ll have some fun.
stefano
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Re: Xerox 820 disk format

Post by stefano »

https://oldcomputers-ddns.org/public/pu ... index.html

40 trk disks, e.g. 820sys5 are the easiest one to boot on x820.

Please note that only the x820 option will work correctly.
The 820ii FDC emulation is not complete and won't boot, I also suggest to avoid wasting time on the other variants (BigBoard, etc..).

I'm trying to get the BigBoard II boot, but the emulation is probably at an earlier stage, the display controller requires a "paged" ROM, after a minimum of emulation code hacking, the first slice is picked:
8002.u52 WRONG LENGTH (expected: 00000800 found: 00002000)
8002.u52 WRONG CHECKSUMS:
EXPECTED: CRC(fdd6eb13) SHA1(a094d416e66bdab916e72238112a6265a75ca690)
FOUND: CRC(a1dc4f8e) SHA1(873fd211f44713b713d73163de2d8b5db83d2143)
bb2.png
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dom
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Re: Xerox 820 disk format

Post by dom »

Unfortunately I've failed at the first hurdle. The only discs that are accepted by the version of mame I'm running just result in a hexdump.

Edit, found a working one here: http://bitsavers.org/bits/Xerox/820/5_inch/
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Re: Xerox 820 disk format

Post by stefano »

you might boot also the other ones, but you need first to select the "SmartaROM" BIOS, change the drive type to sa800, then reset and finally open the floppy images
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dom
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Re: Xerox 820 disk format

Post by dom »

I've added in support for --generic-console - I've conveniently ignored the scroll register.

I've also added a 80x24 super lores display which isn't that great since there's blank pixels around the square.
stefano
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Re: Xerox 820 disk format

Post by stefano »

Super fast!
IMO the idea of an 80x48 mode using comma and apostrophe wasn't that bad ?
stefano
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Re: Xerox 820 disk format

Post by stefano »

It is very nice to see the Dallas game run (and play sounds) on the Xerox 820!
In theory the x820ii is slightly different, because it the only one supporting the 1bit sound and the 4x4 blocky graphics, but at the moment it is not much an issue, because no working emulators exist for it, I'm not expecting further development unless someone owning the original machine will jump in, here or in the MAME team.
dallas.png
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dom
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Re: Xerox 820 disk format

Post by dom »

stefano wrote: Thu May 11, 2023 6:23 amIMO the idea of an 80x48 mode using comma and apostrophe wasn't that bad ?
That's an interesting one, I'll add a graphics mode that will implement 80x48 and fat-pix will switch to 80x24. I think I've seen some targets which have the "volume bar" graphics and an inverse flag but not the usual 4x4 or 3x2 so it'll be useful there.
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dom
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Re: Xerox 820 disk format

Post by dom »

....and I've done just that using a couple of characters that work better than ` and ,

Calling gfx_set_fatpix(1) switches to the 80x24 mode detailed above.
stefano
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Re: Xerox 820 disk format

Post by stefano »

fantastic! if it gets generic we can use it in several cases.
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dom
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Re: Xerox 820 disk format

Post by dom »

Yeah, it's reusable - just a case of adding a table with the 4 characters and including gfx_gencon2.lst - we probably ought to redo Kaypro83 to use it rather than the custom code it's got.
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