Fri Mar 24 11:02:10 PST 2000

Notes on PicoWeb Project "udpdata.pwp"
--------------------------------------

This sample is not really set up to run.  It was used it to test UDP
throughput to a PC using a special version of Perl which was hacked
to do UDP transfers.  For various reasons, we cannot distribute it.

The sample project takes a "trigger" UDP packet from the PC which
tells the PicoWeb how much "dummy" data to send back using one or more
UDP packets.  The response UDP packets are limited to 1024 bytes
of "payload" data.  Therefore, if the PC sends a "trigger" packet
requesting 16K bytes of data, then a total of 16 1024-byte UDP packets
will be sent by the PicoWeb in quick succession.  Using this setup,
we determined the maximum sustained rate at which we could move UDP
data from the PicoWeb to a laptop PC (running Windows NT) with a PCMCIA
Ethernet card was 239 Kbytes/sec.

As for a description of the various routines in this project:

The routine "import_udp" gets called each time a UDP packet is received by
the PicoWeb.  This routine looks at the first two bytes of the incoming
UDP packet and then saves this 16-bit number, the total amount of dummy
UDP data to return.  This routine then zeros the counter which keeps
track of how much UDP data has been returned.  Also, this routine calls
"set_client" to remember the IP address and port of the incoming UDP
packet.  This information will be used to send back one or more response
UDP data packets.

The routine "udp_loop_processing" is called each time through the PicoWeb
"fast idle" loop.  It checks whether any UDP "response" data needs
to be sent.  If so, it uses a routine called "movedata" (see pcode
instruction "pf2x") to setup for UDP data transfer and then build up
the UDP packet's data.  The routine "udp_loop_processing" then calls the
routine "mem_udp_send_client" to complete the checksum the UDP packet
and to send the newly formed packet out on the network.

The routine "set_client" records the IP address and port number from an
incoming UDP packet for later use.

The routine "movedata" is called to setup for creating the data for the
UDP packet.  UDP data is supplied two bytes at a time by a co-routine
whose address is stored in the Z-register.  This co-routine is named
"movedata_next" in this sample project.  Each time this "co-routine" is
called it is expected to supply 16-bits of new UDP data in the Y-register
(after first calling "f2x_checksum" to compute a running UDP checksum).

Note that this project also can send data to the serial port using
"parameters" supplied as part of a GET request's URL, then return any data
the serial port responds with as part of a Web page.  (See CGI routine
"sertest".)  This has nothing to do with the "UDP part" of the project.