because I was sugesting that you would also keep the clocks on the devices
sync'd
and you would want to keep the latency down.

My though train went along the following tracks, now, I may be way off here
so if I am please correct my thinking because I think serial over ip for
emulators would be great, and also allow pc apps to communicate with
software running on an emulators in a way that would be very very useful for
debugging.

the min size of an ip packets is around 64 bytes, I'm not sure how much
extra ethernet adds but is probably mac, id, fragment id, checksum, so say
another 16 bytes,

lets say a simple message (16bytes) uses up 128 bytes (1024bits) from your
physical network connection
thus a 100Mb network can support 100K messages in theory.
and its true that a good 100Mb switch is also duplex,
but I believe (may be wrong here) that the GBA serial device is also duplex
2Mb

lets pretend that our comms message has an 8byte header (device id, packet
number, time, length)
and 8bytes of data.
so 64bits of serial comms uses up 1024bits on the network, we would only get
6.25M of serial data from a maxed out 100Mb network.
may be enought with just two machines back to back, but I would be dubious
about how well it would cope 64bit quantising of the serial data, may
introduce too much latency for some games.

expanding the data portion to say 256bytes, expands the network usage to;
2048 bits of serial uses (1024 + (2048-8)) 3064 bits on the network a
wopping 66M of serial data
but at the expence of only doing 1024 messages per second.

if you have four devices all talking to each other using these larger
packets then you have a chance but the latancy and granularity of the
messages may prove to be too great, to be usefull.

I was never sugesting that a 100Mb network could not handle the data, just
you would have to compromise.

a Gbit network however (being almost as fast as PCI) can easily handle huge
amounts of small messages, allowing you to send a clock sync and 4 2Mb
serial message even if
the data to network usages is 16 to 1024. (1Gb become 16Mb) four devices
kicking out serial messages quantised to 16bits, including a time sync per
packet.

for a company 400quid for a gigabit switch and 70quid a card if not realy a
high price to pay to be able to emulate close to reality serial comms, and
have embedded pc to emulator debugging over a virtual serial connection. and
if the emulators used the serial to sync their clocks then you could single
step one emulator to debug it without disterbing the serial comms sync
between the emulator you are debugging and the other devices that are
freerunning. (infact all devices could be debugged, stoped and restarted at
will without losing the synchronisation). any one who's even tried to debug
a interrupt handler (even with an ice) will know what I'm jibbering on
about.

Mike.

----- Original Message -----
From: "Fatty diZilla" <fattydesign@...>
To: <gbadev@yahoogroups.com>
Sent: Friday, August 02, 2002 2:59 AM
Subject: Re: [gbadev] Multiple GBA Emulation (Debugging Comms.)


> > Have you thought about emulating the serial interface over tcp/ip
> > that way two emulators can run on two or more separate PC's, and all
> > the ...
> > you could even have all the cpu clocks kept in sync with netowrk
messages
> > the emulators may run slow, but accurate with respect to each other.
> >
> > if only gigabit networks where cheaper
>
> Er, why do you need a gigabit network to model the interaction of a two
> megabit serial channel?
>
>
>
>
>
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>
>
>