🚀 go-pugleaf

In article <229@obie.UUCP> wes@obie.UUCP (Barnacle Wes) writes:
>Consider this little GEM :-) gleaned from the Abacus "Atari ST Internals"
>book
[ editied ]
>If you reprogram these bits with 00, it tells the chip not to divide the
>clock, giving you a clock of 500 Khz, which is adequate for a simple,
>small network (like AppleTalk).


The UART used for the MIDI port is an old part, with only a one
character FIFO (does that count as a FIFO?).  500 Kbs is about
50,000 characters per second and with the MIDI hardware such as it is,
the 68000 is going to have to do something for every character received.

At 500 Kbs, the system has approximately 20 microseconds to handle
one character.  The 8 Mhz 68000 in the ST can probably sustain this
rate in a tight loop, but I don't think it can handle the 100,000
or so interrupts per second necessary to handle a bi-directional 500kps
interrupt driven link (i.e. "background" network).  This is before
you consider that other ST interrupts have a higher priority than
the MIDI UART interrupt and any one of these other interrupts (e.g.
RS-232) might take well over the 20 microsecond time limit.

This scheme may be usefull for a "dedicated" server under extremely
controlled conitions, such as printing while the system isn't doing
anything else, but it is *very* unlikely that it could be used for
a LAN type architecture.
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