> -----Original Message-----
> From: Maarten ter Huurne [SMTP:[EMAIL PROTECTED]]
> Sent: Monday, March 08, 1999 12:36 PM
> To: [EMAIL PROTECTED]
> Subject: RE: Diskrom modifications
>
> At 09:30 AM 03/08/99 +0100, you wrote:
>
> >> You only have to implement the I/O routines located at #4010 and higher
> >> (get DPB, read sector, disk change, format etc). You don't even need
> the
> >> other routines, because they are already located in the main diskROM.
> >
> > But if you do this, I guess it is not possible anymore to use the
> >normal diskdrive, or...
>
> No.
> The way I do it, it's partially true. After I activate the JoyNet drive, I
> will have 1 normal diskdrive instead of 2.
> But if you do it the right way (insert at boot time), you will simply have
> more drives. For example ESE-SCC RAMdisk adds itself as drive A:, where B:
> and C: are the normal drives.
This was the hard part, right?
> >I was also thinking of a way to use the
> >joystick-interface, but then use 4-bit parallel or 8-bit parallel in one
> >direction and 1 or 2 bit in the other direction (because I guess reading
> >will occur more often than writing).
>
> Joystick interface is not such a good choice, in my opinion.
> There are several problems:
> - only 3 bits to write and 6 bits to read, where 2 of those (triggers) are
> either read or write but not both
> - switching from read to write requires selecting a different PSG register
> (code execution time overhead)
> - the BIOS messes around with the values of the joystick port (see recent
> thread in this mailinglist). One problem that wasn't mentioned yet is that
> when an MSX is switched on, the values on the joystick port change. This
> can cause problems if the other side (server on PC) is already running.
> - you already need joystick ports to connect a joystick or a JoyNet cable
I thought of this solution only because no additional hardware is
needed, but I agree a separate interface is much better.
> My suggestion is that you build the connection hardware in a cartridge.
> Since you wanted to use a ROM, you'll have to make one anyway.
>
> To access it, you could define 4 ports:
> - input port: 8 bits data
> - output port: 8 bits data
> - status port: tells you when new data has arrived and when you can send
> - control port: turn on/off certain features (if necessary)
> You could map them either to I/O ports or to memory addresses. You can use
> the same addresses for the input port and the output port, if that
> simplifies the design. The same for the control and status port.
>
> To get optimal transfer speed, it would need a small buffer. Maybe a
> single
> byte is already enough.
>
> The protocol I used for the JoyNet drive is very simple. When the MSX
> needs
> something done, it sends a 4-byte request. Examples are:
> db GET_SECTOR
> dw first_sector
> db nr_sectors
> and
> db GET_DISKCHANGE
> db 0,0,0 ;undef
>
>
>
> The length of the reply depends on the command. For a sector read, it is a
> status byte, possibly followed by 512 bytes of data. The status byte is 0
> if the read succeeded or a non-zero error number if it failed.
>
> Maybe you'll want a bit that signals "end of transmission". It would be
> nice to have, but not necessary: you can design a protocol that always
> knows how long the message is that it's going to receive.
>
As I mentioned, I'm thinking of using an ARCnet interface. I found
out some more data on this. It only needs a little hardware (a COM20020 and
some line drivers) and has a lot of features to keep the software part as
simple as possible. And there should be a lot of these PC-cards around.
Some features:
- Built in RAM 2k*8 in four 512 byte pages
- CRC check
To send something, you can fill a RAM page and issue a command
'SEND' + ID of receiver, and the rest is handled by the controller. The same
goes for receiving: just issue 'RECEIVE to page nn' and the rest is
automatic. The interface consists of 8 r/w ports, most of which are not
needed for this application.
Filling RAM is easily done by sending the start address and then
'pumping' the data to the data port (the controller auto-increments the
address counter).
Another advantage, but not really necessary: you can use more than
one MSX on the same server. It is also possible to use another MSX as a
server, but I guess that will be quite slow. But nevertheless...
Do you know which 8 consecutive ports I can use safely ?
Greetz
Patrick
****
MSX Mailinglist. To unsubscribe, send an email to [EMAIL PROTECTED] and put
in the body (not subject) "unsubscribe msx [EMAIL PROTECTED]" (without the
quotes :-) Problems? contact [EMAIL PROTECTED] (www.stack.nl/~wiebe/mailinglist/)
****
