flashx20 - Floppy and screen for the Epson HX-20

[allison]

On 12/16/2018 11:56 PM, Fred Cisin via cctalk wrote:
>> On December 16, 2018 at 11:14 PM allison via cctalk
>> <cctalk at classiccmp.org> wrote:
>>>
>>>> On Sun, 16 Dec 2018, Norbert Kehrer via cctalk wrote:
>>>>> I have not tested it, but I suppose, that also the PX-8 and PX-4 used
>>>>> the protocol,
>>>>> because the protocol specification defines the following device
>>>>> numbers:
>>>>> - HX-20: 0x20 (probably also used for the HC-20)
>>>>> - PX-8:  0x22
>>>>> - PX-4:  0x23
>>>>
>>>>
>>>>
>>> PX-8!
>>>
>> A subject dear to me.  I still have the px-8 I bought new (borrowed
>> the money from my sister) as a young man in 1984.  Alas, I could
>> never afford the PF-10 disk drive.
>>
I've had one for many decades and 2 more for well, now its two decades.
Handy little critter and they do see use.
>>
>>>> However, the PX-8 3.5" had 40 cylinders, with 67.5 tpi, instead of the
>>>> common 80 cylinder 135 tpi of other 3.5" disks.
>>>> Those 40 cylinder 3.5" drives are quite rare.
>
> On Sun, 16 Dec 2018, Will Cooke via cctalk wrote:
>> Somewhere in my searches I recall reading that the 3 1/2" drives used
>> the same format as the 5 1/4" ones.  Maybe 40 tracks of 16 256 byte
>> sectors.  Oddly, I believe that 2 tracks are "reserved for CP/M" even
>> though it is in ROM and not stored on disk.
>
> It was not uncommon for CP/M disks to have "reserved" or "system"
> tracks, even when the particular disk was not a bootable "system" disk.
>
Standard SSSD 8" that is the case the fist two tracks are for "system"
and the system is loaded from those.
Most other do a variation depending on format and space.  CP/M ( the
modules CCP, BDOS, BIOS) fits in about 8k
so that defines the size of system tracks. 

CP/M revolves around logical sectors of 128 bytes so anything larger
2556/512/1k requires
blocking and deblocking in the bios.

> I don't remember for sure, and don't have convenient access to my
> materials, but 16 256 byte physical sectors makes sense.
>
Yes, it would be enough.  Save for the PX8 has CP/M loaded into ROM so
the system tracks are largely wasted.
I believe there is some drive and system level configuration information
there but we are talking less than
a sector or two.

> The drive manual
> http://electrickery.xs4all.nl/comp/px8/doc/PF-10Manual.pdf
> SAYS 9 512 byte sectors, but that seems likely to be in error from a
> cut and paste boilerplate from a different machine, because the more
> specific information is all for "64 sectors", which means CP/M RECORDS
> or "logical sectors" of 128 bytes each.  THAT would be consistent with
> either 8 512 byte PHYSICAL sectors, or 16 256 byte PHYSICAL sectors.
>
It seems that way as it matches the PF-20 5.25" drive.  However the
format on the drive also seems consistent at 9x512.
Its not uncommon to use the whole system track or two even if it has
"excess" space. Often the first sector contains the full
disk book rather than a minimal 1 sector boot.  There is a lot of
latitude and mostly why copy format programs such as yours
existed due to same drive and media and many many different formats.


I've gotten away from rotating media on a few of my CP/M systems and
they go to the edge of what CP/M permits
as in EPROM loaded, ROMdisks, RAMdisks and CF.


Allison