GTCO CR 1212 - Users Guide - Manual (Page 32)

CR 1212 32
Chapter 5: Guidelines for Writing a Device Driver
For the computer to make use of the data being sent to it from the tablet, the software
(system or application) must contain a tablet device driver. The driver needs to be written
for your specific CR 1212 configuration (Bit Pad One, Bit Pad Two or CR). The device driver
is a program that collects and decodes the tablet data.
The driver usually sits between the application and serial interface. The driver should be
able to:
 Receive reports and status information from the tablet via the serial interface
 Transmit data to the application
 Present high level commands from the application that control the tablet
A typical driver consists of four major parts:
 Configure Host and Tablet
o Structure the host communications port (port address, baud rate, etc.)
o
Shape the tablet (resolution, report mode, etc.)
 Report Collection – Interrupt Routines
o
Assemble the report: collect the report’s data bytes into an array
o
Check for errors
 Process Reports from the Tablet
o
Decode the report
o Filter reports, if required by the application
o
Notify the application, if applicable, that a report is ready to be issued to the
application
 Process Errors
o
Parity errors
o Short report errors after time-out
o
Long report errors
o Missing report errors after time-out
o
Host buffer full errors (automatic XON/XOFF support)