X25AM Programming Manual

PTP Applications

X25AM Programming Manual—527201-001

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Mode 0

Your application processes a logical record in a single file-system operation. The

logical record always consists of data. PTP does the following:

•

Disassembles a logical record written by your application into one or more data

packets. The M bit is set to 1 in all except the last packet.

•

Assembles data from one or more packets into a logical record for your application

to read.

The logical record must fit in the file-system buffer. The maximum buffer size is

determined by MAXIOSIZE. Therefore, the maximum record size cannot exceed

MAXIOSIZE. Packet types and application buffer contents used for mode 0 are shown

below:

•

Acceptable packets: Data packets

•

Buffer contents: Data for or from all packets needed for a logical record

READ Request

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

filesystem buffer contains the data for an entire logical record that has been assembled

from one or more packets by PTP.

READ COUNT can vary for each logical record but cannot exceed MAXIOSIZE. When

the READ completes successfully, COUNT READ indicates how much data was read.

If the logical record length exceeds READ COUNT, the extra data (logical record length

minus READ COUNT) is discarded. No error is returned.

Data packets can have the Q bit set to 0 or 1. When the data is transferred to the

application (in the form of a logical record), the application has no way of knowing the

value of the Q bit.

WRITE Request

Your application posts a WRITE to a subdevice. When the WRITE begins, the

filesystem buffer must contain data for an entire logical record, which will be

disassembled into one or more packets by PTP. Each data packet will have the Q bit

set to 0. All data packets except the last one have the M bit set to 1.

WRITE COUNT can vary for each logical record but cannot exceed MAXIOSIZE.

WRITEREAD Request

Your application posts a WRITEREAD to a subdevice. The WRITEREAD is processed

as a WRITE followed by a READ. When the WRITE portion completes, the request is

moved to the end of the READ queue.