3 control information buffering, 4 medium irda specific features, 1 introduction – Cirrus Logic EP93xx User Manual
Page 604: 1 bit encoding, 3 control information buffering -8, 4 medium irda specific features -8, 1 introduction -8, 1 bit encoding -8
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Copyright 2007 Cirrus Logic
IrDA
EP93xx User’s Guide
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17.3.3 Control Information Buffering
The ARM Core needs several items of information about a received frame that are not held in
data DMAed from the
receive FIFO, or stored in the DMA controller itself (because the DMA unit
may be receiving the next frame by the time the ARM Core starts to work on the frame just completed).
The additional information is as follows:
•
A receive overrun or framing error occurred during frame reception.
•
The frame failed the CRC check at the end of reception.
•
Transmission of the frame was aborted.
•
The number of bytes of valid data received in the frame (i.e. up to the end of frame or the
overrun/framing error
condition).
A control information buffer register is loaded whenever an end of received frame condition occurs.
This event also generates an interrupt, which must be serviced before the end of the next received
frame (at which point the buffered control information would be overwritten). The interrupt may be
cleared by reading from the control information buffer
register or by writing a ‘1’ to its status bit
position.
17.4 Medium IrDA Specific Features
The MIR comprises a dedicated serial port and RZI modulator/demodulator supporting the
Infrared Data Association (IrDA) standard for transmission/reception at 0.576 and
1.152 Mb/s.
Frames contain an 8 bit address, an optional control field, a data field of any size that is a
multiple of 8 bits and a 16-bit CRC-CCITT. The start/stop flag and CRC generation/checking
is performed in the hardware. Data can be selectively saved in the receive buffer by
programming an address with which to compare against all incoming frames. Interrupts are
signalled when CRC checks performed on received data indicate an error, when a receiver
abort occurs, when the transmit buffer underruns during an active frame and is aborted, when
the receive buffer overruns and data is lost.
17.4.1 Introduction
17.4.1.1 Bit Encoding
The MIR bit encoding uses an RZI modulation scheme where a “0” is represented by a light
pulse. For both 0.576 and 1.152 Mbps data rates, the optical pulse duration is normally 1/4 of
a bit duration. For example, if the data frame (in the order of transmission) is 11010010b, then