🚀 go-pugleaf

In article <486ur1$hpk@unidhp.uni-c.dk>, Rask Lambertsen writes:

> 1) Fast - at least 115300 baud.
> 2) Should work on 7MHz 68000.
> 3) Easy to built, even for those not too experienced in hardware hacks.
> 4) Cheap.
> 5) Should be installable in A500/A600 as well as A1000/A2000/A3000/A4000.

With respect to 5) I guess the only two ports that all machines share are
the serial and the parallel port.

Both cause one interrupt per byte, and both have a speed limit far beyond
of what we need.

In  my  opinion a solution for the above is to build a card that plugs into
the  serial  or the parallel port and decouples the computer DTE speed from
the modem DTE.


On  the serial port this would make:  the computer talks to the card at the
max of 292,000bps, the card buffers the data and passes it at whatever rate
is desired - for example 57,600bps.

When receiving data from the modem, the card puts it into a buffer.  If the
buffer  was empty before, it also feeds it to the computer (causing a level
2  interrupt).   The  software driver notices this and start a CIA-B timer.
It  expires  a  few  ms later (whatever time is needed to 3/4 fill the card
buffer) and causes a level 6 interrupt (which is highest pri in amiga).

From  this  interrupt  code the driver can empty the buffer at 292,000bps -
without  returning  control  to  the  OS between the bytes to not risk data
loss.  Even a 68000 can _poll_ the serial port at high bps rates.

Possible problems:

· breaks 250us limit for interrupts when using a buffer of more than x
  bytes (depending on bps)



Advantages of the parallel over the serial port:

· internal serial port remains usable -> two modems can be connected

· easier communication computer-->card (ie sending the baud rate information)

· computer<->card max bps rate dependant on CPU only


Maybe we could make a DIP-Switch selectable bps rate to save lots of parts.