TOPS-10 Monitor Calls Manual Volume 2 AA-K039D ... - Trailing-Edge

IPCFR. [CALLI 142]
22.73 IPCFR. [CALLI 142]
FUNCTION
Retrieves a packet from the IPCF input queue for the calling process.
The IPCF facility and the format of the argument blocks are described
in Chapter 7.
CALLING SEQUENCE
MOVE ac, [XWD len,addr]
IPCFR. ac,
error return
skip return
addr:
EXP
BLOCK
XWD
flags
2
len2,addr2
addr:
BLOCK len2
In the calling sequence, the program supplies the following variables:
o
o
o
len is the length of the packet header block.
addr is the address of the packet header block.
flags is the flag word (.IPCFL) in the packet header block.
o len2 is the length of the packet to be retrieved. If the
packet is going to be a page of data, this field must contain
512 or an error code is returned in the ac and the IPCFR.
monitor call takes the error return.
o
addr2 is the address of the packet message block.
The retrieving process should check the contents of the flag word. If
there is an error condition associated with the packet, it will be
indicated in bits 24-29. Error codes rece~ved in the ac indicate an
error with the monitor call (for example, if the-packet was not
received) .
If the IPCFR. monitor call is issued but there are no packets in the
input queue, the job cannot continue executing until a packet is
placed in the input queue. To prevent the job from blocking, bit 0
(IP.CFB) should be set in the flag word. When IP.CFB is set and there
are no packets in the input queue when the IPCFR. call is issued, the
call will take the error return and the monitor will return error code
3 (IPCNT%) in the ac.
When a process is retrieving a page of data, bit 19 (IP.CFV) in the
flag word must be set and the length of the data message block (left
half of . IPCFP) must contain 1000 or the IPCFR. monitor call fails
and the monitor returns error code 21 (IPCPR%) in the ac.
If the retrieved packet is shorter than the number of reserved words
(that is, len2), the packet is retrieved and the extra words are left
unchanged. -rt; however, the number of reserved words is not long
enough to store the packet, the IPCFR. monitor call takes the error
return and the monitor returns error code 5 (IPCTL%) in the ac. To
prevent this error, the receiver can set bit 4 (IP.CFT) in the flag
word indicating that, if the packet is too long for the reserved
space, the message should be truncated.
22-188