X25AM Programming Manual

PTP Applications

X25AM Programming Manual—527201-001

3-8

Mode 1

Your application can process data that goes into or comes from a single data packet or

a single interrupt packet. Data for one packet is written into or read from the filesystem

buffer. The first word in the buffer is the MCW. The rest of the buffer contains data or

interrupt data.

A logical record can consist of data from more than one data packet. Assembly or

disassembly of the logical record using data and sequential file-system operations

(such as READ, READ, READ or WRITE, WRITE, WRITE) are the responsibility of

your application. The M bit in the MCW determines whether the data in the buffer is the

end of the data for the logical record.

The READ COUNT should always be equal to PACKETSIZE + 2. The WRITE COUNT

should never exceed PACKETSIZE + 2. PACKETSIZE can be negotiated when a call

is made, so its current value might not be the configured value. One solution to this

problem is to prohibit packet size negotiation. If packet size negotiation is configured

with the SCF subdevice attribute NEGOTIATE PACKETSIZE, your application should

use mode 3.

Packet types and application buffer contents used for mode 1 are shown below.

READ Request

Your application posts a READ to a subdevice. When the READ completes, the first

word (bits <0:15>) in the file buffer is the MCW. Bit <13> indicates whether the rest of

the buffer contains data from one data packet or one interrupt packet.

If the M bit equals 1, then the logical record consists of data from more than one

packet. The current data is not from the last packet. Continue posting READ

statements until the M bit equals 0, indicating that this data is from the final packet.

Acceptable packets:

Data packets

Interrupt packets

Buffer contents:

MCW One data packet

Table 3-3. Message Control Word Used for Mode 1

Bit Number Bit Value Bit Name Meaning

<0:12> 0

<13> 0 This is a data packet.

<13> 1 This is an interrupt packet.

<14> 0 Q bit This is really data.

<14> 1 Q bit This is some other kind of

information.

<15> 0 M bit This is the final packet.

<15> 1 M bit This is not the final packet.