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AN16
SX IrDA Virtual Peripheral Implementation
If the application was simplex (one direction only), for
example a printer, then the data could be buffered as the
SX would be capable of buffering a 62 byte frame. It is
not, however, capable of buffering both a 62 byte transmit
and a 62 byte receive frame.
The application layer cannot call the LMP layer. Instead
the LMP layer will call the “event handlers” in the applica-
tion layer as specified in Figure 3-10. An event handler
should be in the following form:
lmp2appRxCommData
bank
ApplicationBank
;Correct local register bank
...
;Event handling code
retp
;Paged return
For reception the LMP layer will call the application
layer’s lmp2appRxCommData event handler with the
data byte in the w register. The application is free to pro-
cess the byte however it must return when it has finished
processing the data and cannot hold up the CPU waiting
for something to happen. This event handler will be
called for every IrComm data byte in the incoming frame
(up to 62 times) before the LMP layer calls
lmp2appRxCommValid
to
validate
the
data
or
lmp2appRxCommError to reject the data.
For transmission the LMP layer will ask if there is any
data to be sent by calling lmp2appTxCommStart. The
application layer should return z clear if there is data to
send. For example:
lmp2appTxCommStart
bank
ApplicationBank
;Correct local register bank
test
DataCounter
;Z is set if no data to send
retp
;Z is clear if data to send
If the application layer indicates that there is data to be
sent then the LMP layer will call lmp2appTxCommData
when it is ready to transmit the first byte of data. The
application layer must return with w containing the data
byte to be sent and z indicating if there is more data to be
sent. If z is true then this is the last byte to be sent and no
more data will be requested. If z is false then another
byte will be requested when the LMP layer is ready to
accept it. The LMP layer will accept up to 62 bytes of
data for a frame thus the 62nd byte will be considered to
be the last byte by the LMP layer regardless of the z flag.
lmp2appTxCommData
bank
ApplicationBank
;Correct local register bank
mov
w, DataPointer
;w = Pointer to register with data
inc
DataPointer
;increment pointer to next register
mov
FSR, w
;apply register pointer
mov
w, INDF
;w = data to send
bank
ApplicationBank
;ensure correct register bank
dec
DataCounter
;Z is set if no more data to send
retp
;Z is clear if more data to send
lmp2appRxCommData (w=data)
Incoming IrComm data.
lmp2appRxCommValid ()
Data bytes passed since last Valid/Error message have been validated.
lmp2appRxCommError ()
Data bytes passed since last Valid/Error message are erroneous.
lmp2appTxCommStart (ret z=none)
A request to find out if the application has IrComm data waiting to be
sent.
lmp2appTxCommData (ret w=data, z=last)
A request for IrComm data so that it can be transmitted.
lmp2appTxCommValid ()
All data passed since last Valid/Error message were acknowledged as
received by the remote station.
lmp2appTxCommError ()
All data passed since last Valid/Error message were discarded and will
need to be sent again.
Figure
3-10. IrComm API
