FIR Coding
This topic discusses how IrDA miniport drivers and their infrared NICs code frames for transmission at Fast IrDA (FIR) link speeds. The FIR specification defines short-range low power operation at 4Mbps (half duplex). All FIR devices are also required to support SIR operation.
For FIR link speeds, an entirely different coding scheme, called four pulse position modulation (4PPM), is used. The 4PPM coding scheme defines special flags for BOF and EOF. The 4PPM coding scheme should always be implemented in hardware.
The IrDA miniport driver might still be required to calculate the CRC to validate the frame. For FIR link speeds, a 32-bit CRC is used. An algorithm for calculating the 32-bit CRC is available in the publication Infrared Data Association Serial Infrared Physical Layer Link Specification available from IrDA.