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CB030 Compact Flash disks [message #9324]

Sun, 31 October 2021 11:01

curbie
Messages: 55
Registered: June 2021

Member

One of the many questions I need verification on is Compact Flash disk structure as I understand it

62tracks x 1024sectors x 128bytes/sec=8,126,464 bytes within CP/M or

0-15,871(36FFh)LBAs x 512bytes/sec=8,126,464 bytes for native Flash drive

So my question is what occupies the Flash disk space after LBA 36FFh from 3E00h to FC2F700h, it seems like nothing and that's where I'm thinking to create a disk for another computer.

Do I have anything goofed up?

Curbie

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Re: CB030 Compact Flash disks [message #9328 is a reply to message #9324]

Sun, 31 October 2021 13:43

norwestrzh
Messages: 196
Registered: November 2015

Senior Member

I use a 4k allocation unit, and 128 (CP/M) sectors per track. So 16,384 bytes per CF "track". An 8 MB CP/M file system uses 512 "tracks". I experimented with file systems larger than 8 MB, but the directory scan when first accessing the thing was quite painful. I just define sixteen 8 MB "drives". Seems adequate.

This is how I calculate the LBAs:

___LBA2_|___LBA1_|___LBA0_|
xxxxxxDD|DDTTTTTT|TTTSSSSS|

Takes a little bit juggling to set that up, but it seems to work well.

>> So my question is what occupies the Flash disk space after LBA 36FFh from 3E00h to FC2F700h,
>> it seems like nothing and that's where I'm thinking to create a disk for another computer.

On my file system layout, nothing. If you can address to it without interfering with your CP/M file system(s) at the low end of the CF, then have at it!

Roger

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Re: CB030 Compact Flash disks [message #9332 is a reply to message #9328]

Sun, 31 October 2021 18:07

plasmo
Messages: 916
Registered: March 2017
Location: New Mexico, USA

Senior Member

Curbie,
CB030 has 4 8-meg drives. CP/M allows up to 16 drives so technically it can use up to 128meg CF disk. Currently LBA above 00_FF_FF are not use by CP/M68K as implemented by CB030.
Bill

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Re: CB030 Compact Flash disks [message #9337 is a reply to message #9332]

Mon, 01 November 2021 07:26

curbie
Messages: 55
Registered: June 2021

Member

Roger & Bill,

Thanks, I'm thinking about many notions for porting, and it seems to me that I should probably chase them all in the hope I can push one through to the end.

Curbie

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