TOPS-20 UDP: device
Phil Budne @ Boston University / DSG

GTJFN%

Syntax is  like  TCP:, but  the  only attributes  are  LOCAL-HOST  and
FOREIGN-HOST (taking dotted decimal  octets ie; 54.0.0.20).  Only  one
open JFN per system can hold any local port at any time.  Receives are
independant of the 4n host/port (4n side looked at only for sends).

Local port numbers are assigned as with TCP: if not specified by the
user. (Cheats by using the same job unique number counter).  Perhaps
the number should be assigned at OPENF% time?

I tried to fix some of the problems with host names in GTJFN%, but
without success.

OPENF%

The legal byte sizes are 8. and 32.  The only legal I/O mode is 0.
All I/O is done "high thruput".  That is a packet is sent when the
current one is filled.  SIN and BIN will read across packet boundries,
while SINR will stop at the end of the current packet.  SOUTR will
force a 'PUSH' of the current packet.  There is a bit in the UCB for
interactive / hi-thruput, but I forget how much code there is to
support it, in any case the bit is always lit.  Interactive doesn't
seem like a great idea for most UDP applications anyway.

GDSTS%

returns:

AC2/	Count of packets waiting for input; system will only hold the
	first <n> unread packets (currently 10.)  before dropping new
	packets on the floor.  I have thought of keeping track of how
	many packets have been thrown on the floor since the last
	read, and returning it in the left half.
AC3/	4n port of last packet.
AC4/	4n host of last packet.


MTOPR%

The MTOPR code usually does a linear search, so why not use SIXBIT!!

.MOUOU==:'UOU'			;BLOCK OUTPUT FUNCTION
	.UDLEN==:0		;LENGTH OF ARGBLOCK (INCLUDING THIS WORD)
	.UDBUF==:1		;ADDRESS OF BUFFER CONTAINING L.JUST. OCTETS
	.UDSIZ==:2		;OCTET COUNT
	.UDADR==:3		;(OPTIONAL) INTERNET FOREIGN ADDRESS
	.UDPRT==:4		;(OPTIONAL) FOREIGN PORT

I've never tested this one!!

.MOUPS==:'UPS'			;ASSIGN PSI CHANNEL

Argument in channel.  Channel 077 clears interrupts.  This functions
reassigns JFN ownership.