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The PTOP data-exchange calls are master-slave. The master
initiates an exchange by calling PWRITE (to send data to the slave), PREAD (to receive data from the slave) or PCONTROL. The slave calls GET to receive the request and ACCEPT to perform the actual data movement into or out
of its buffer. Each of these operations may also exchange a tag between
the master and the slave. The master call sends the master tag to
the slave and returns a tag from the slave. The slave's GET call receives the master tag. The slave's ACCEPT or REJECT call returns the slave's tag to the master. The GET intrinsic can return an indication of the master
request (0 = error, 1 = POPEN, 2 = PREAD, 3 = PWRITE, 4 = PCONTROL). In many applications, the slave will always
know the next request that it will receive from the master, so the
function returned by GET is superfluous. But in some applications, the
slave does not know in advance what the next master request will
be, and so it depends on the GET function to decide on its response to the request.
The GET call can also return the requested length of data
to be sent or received. These applications typically have a loop
with a GET that receives the master requests and a case statement
with cases for each of the different functions. Data exchange with NetIPC is peer-to-peer. A process on either
side of a virtual-circuit connection can send or receive data independently
from its partner. The master-slave data exchange of PTOP can be
simulated using NetIPC calls. For example, a PWRITE in the master can be replaced by an IPCSEND, while the corresponding GET and ACCEPT in the slave can be replaced by an IPCRECV. Tags can also be exchanged using sends and receives. In applications where the sequence of master requests is not
known by the slave, or where the length of data sent to or received
from the slave is not known, some information in addition to the
exchanged data and tags may need to be transmitted. This includes
a) a master request indication, b) master request lengths, and c)
the slave accept or reject indication. Because of the way that NetIPC stream mode operates on the
HP 3000, an IPCRECV may not receive all of the data requested. For
this reason, we recommend that you write a procedure that calls IPCRECV in a loop to receive chunks of data until the
entire requested amount is received. An example of this is in Chapter 4 “NetIPC Examples” in this manual. Exchanging Data: In the Master Program | |
To convert the PTOP intrinsic listed below, perform the following
steps. lgth := PREAD (dsnum,target,tcount[,itag] |
If the slave requires a master function,
send the PREAD request function (=2) on the virtual circuit to
the slave. If the slave requires the requested data length,
send tcount on the virtual circuit. If a tag is specified, send the master tag on the
virtual circuit. If the master needs to know the actual data length
sent from the slave, receive the actual data length from the virtual
circuit. If the slave may call either ACCEPT or REJECT, receive a one byte accept or reject indication
on the virtual circuit from the slave. Otherwise assume the slave
accepted the request. If the slave accepted the request, receive the target
data from the slave, using either a predetermined length or the
actual data length received in Step 4. If a tag is specified, receive the slave tag from
the virtual circuit.
To convert the PTOP intrinsic listed below, perform the following
steps: Syntax | |
PWRITE(dsnum,target,tcount[,itag] |
If the slave requires a master function,
send the PWRITE request function (=3) on the virtual circuit to
the slave. If the slave requires the requested data length,
send tcount on the virtual circuit. If a tag is specified, send the master tag on the
virtual circuit. If the slave may call either ACCEPT or REJECT, receive a one byte accept or reject indication
on the virtual circuit from the slave, Otherwise assume the slave
accepted the request. If the slave accepted the requested, send the target
data on the virtual circuit to the slave, using the tcount length. If a tag is specified, receive the slave tag from
the virtual circuit.
To convert the PTOP intrinsic listed below, perform the following
steps. Syntax | |
If the slave requires a master function,
send the PCONTROL request function (=4) on the virtual circuit to
the slave. If a tag is specified, send the master tag on the
virtual circuit, and receive the slave tag from the virtual circuit.
Exchanging Data: In the Slave Program | |
To convert the PTOP intrinsic listed below, perform the following
steps. Syntax | |
ifun := GET [([itag][,il][,ionumber] |
If the slave requires a master function,
receive a one byte master function number from the virtual circuit
from the master. If the slave requires the request length, receive
the length from the virtual circuit. If a tag is specified, receive the master tag from
the virtual circuit.
To convert the PTOP intrinsic listed below, perform the following
steps. Syntax | |
ACCEPT [([itag[,target][,tcount)] |
Depending on the master function,
either known to the application, or received from the master in
Step (1):
PREAD: Send the target data, of length fncttcount, on
the virtual circuit to the master. PWRITE: Receive the data into target, using either the
known fncttcount or the length received from the master in Step
(2). If a tag is specified, send the slave
tag on the virtual circuit.
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