Carrol Touch TouchSystems CarrollTouch Prog, Руководство программиста

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CARROLL TOUCH Chapter 5 - Smart-Frame Protocol II
Touch System Programmer’s Guide 5-7
Validation Layer
The format for SFP-II commands at the validation layer is:
header packetbytecount interpretationlayer
trailer
The validation layer consists of the outer portions of the command
format and “wraps” around the inner portions of the command format,
or the interpretation layer. To detect a valid SFP-II command in the
incoming stream of bytes, the touch system firmware detects the
header, reads the byte count that follows the header, reads the number
of bytes specified by the byte count (the command packet), and verifies
that the following byte is a trailer byte. If the segment of the incoming
byte stream under consideration fits this format, the segment is deemed
to be a valid SFP-II command packet and the command number and
parameters are forwarded to the interpretation layer.
Interpretation Layer
The format for SFP-II commands at the interpretation layer is:
commandnumber optionalparameters
To interpret the command, the touch system firmware first jumps to the
appropriate command handler using a jump table. If the command
number does not correspond to a defined SFP-II command, the
command is deemed invalid and a report is sent to the host with the
command error parameter set to the Invalid Command value.
If the command handler determines that the appropriate number of
parameter bytes for the command is not present, or that one or more of
the parameter bytes are otherwise invalid for the command (parameter
is out of range, not set to a valid value for this particular touch system,
and so forth), the corresponding SFP-II report is sent to the host with
the command error parameter set to indicate the missing or invalid
parameter byte. The parameters that the host sent in the command are
echoed to the host in this report.
If the command handler determines that the appropriate number of
parameter bytes for the command is present and that all of the
parameter bytes are valid for that command, the touch system processes
the command and sends the corresponding SFP-II report back to the
host. The command error parameter is set to the “valid command and
parameters” value to indicate that both the command and parameters
were valid.