Erlang to driver communication: why not a non-serialized option?

Vance Shipley <>
Thu Apr 25 12:24:29 CEST 2002


Scott,

Thanks for pointing out the new features in erl_driver et. al.

There are a number of improvements:

	- ease of encoding complex erlang terms 
	- zero copying of terms
	- ability to send terms to arbitrary processes
	- registered port names

The latter allows a good deal of optimization for some uses.
I am rewriting our driver for the Netaccess LAPD/MTP2 boards
to use all of these features.

One thing that seems odd at first glance is that when doing 
syncronous calls from erlang into the driver the terms are 
sent and received in a different format than the asyncronous
functions used to send terms from the driver to erlang.

When erlang:port_call/3 is used the driver's callback is 
passed a buffer which can be decoded with the functions in
the ei library (part of erl_interface).  The same library
is used to encode the response to the erlang port.

The erl_driver functions driver_output_term() and 
driver_send_term() use "the driver term format".  There are
a set of functions for doing some of this encoding but they
are entirely different than ei.

I guess it goes with what you were saying about there being
some increasing differences between drivers and ports.

	-Vances

--
Vance Shipley
Motivity Telecom Inc.
+1 519 579 5816
                        



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