Gtco CR 1212 - Users Guide Manuel d'utilisateur télécharger pdf (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)

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Gtco CR 1212 - Users Guide Manuel d'utilisateur Page 32