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processor-intensive, it is strongly recommended that this logic be
implemented in hardware. At MIR link speeds, two BOF flags are
required on every frame.
For MIR link speeds, the CRC used is the same as for SIR speeds. That
is, for MIR link speeds, the IrDA miniport driver also typically calcu-
lates the CRC value, rather than the driver’s hardware.

FIR Coding
This topic describes how IrDA miniport drivers and their IR NICs code
frames for transmission at Fast IrDA (FIR) link speeds. The FIR speci-
fication defines short-range, low-power operation at 4 Mb/s (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. Always implement the 4PPM
coding scheme in hardware.
The IrDA miniport driver may still be required to calculate the CRC to
validate the frame. For FIR link speeds, a 32-bit CRC is used. An algo-
rithm for calculating the 32-bit CRC is available in the publication
Infrared Data Association Serial Infrared Physical Layer Link
Specification, available from IrDA.

VFIR Coding
This topic describes how IrDA miniport drivers and their IR NICs code
frames for transmission at Very Fast IrDA (VFIR) link speeds. The
VFIR specification defines short-range, low-power operation at 16
Mb/s (half duplex). All VFIR devices are also required to support FIR
and SIR operation.
For VFIR link speeds, an entirely different coding scheme, called
HHH(1,13), is used. The letters HHH that represent this coding scheme
are the initials of the three researchers who invented it. Always imple-
ment the HHH(1,13) coding scheme in hardware. For more informa-
tion on HHH(1,13), see the publication Infrared Data Association
Serial Infrared Physical Layer Link Specification, available from IrDA.
The IrDA miniport driver’s hardware can calculate the CRC to validate
the frame. However, if hardware does not calculate CRC, the IrDA

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