Program Interface Library AR_TIMETAG_CONTROL
CEI-100/CEI-200/CEI-x20 User’s Manual 149
AR_TIMETAG_CONTROL
CEI_INT16 ar_timetag_control (CEI_INT16 board, CEI_INT16 flag);
The ARINC interfaces can generate a timetag for received data with a
resolution equal to the timer rate that is programmed by the routine
AR_SET_TIMERRATE, with a resolution of 32 bits. This timetag is
stored in the receive buffer along with the data that it is tagging. Since the
storage of a timetag effectively halves the size of the receive buffers (i.e.,
an ARINC word input is 32 bits plus a tag of 32 bits requires 64 bits of
storage versus only 32 bits for a data-only buffer) the routine allows for
selective enabling and disabling of the timetag. When time tagging is
enabled, the interface automatically appends a timetag to each received
data word as it is read off the bus. By default, time tagging is disabled.
The timetag indicates the time the data was put into the buffer by the
interface. Since one interface controls up to sixteen channels, there may
be some skew of the time tag, depending upon circumstances. For
example, if two receive words come in simultaneously, the interface
processes each one sequentially. Each word has a slightly different time
tag. The skew should not be more than 360 microseconds, or the
resolution of the time tag, whichever is greater. The CEI-100/200
receivers are interrupt-driven and the interrupts are handled in order of
priority with receiver 8 being the highest and receiver 1 the lowest. The
CEI-x20 receivers and transmitters are processed in “round-robin” fashion.
This routine must be called when the interface is in a reset state, prior to
calling AR_GO (CEI-100/200 only). For CEI-x20 cards, this routine must
only be called when you are certain that the receive buffers for all
impacted channels are empty and the interface is not actively receiving
traffic on the channel(s) in question. When time tagging is enabled, use
AR_GETWORDT (or AR_GETNEXTT) to get the data. Don’t use
AR_GETWORD, which is for non-time tagged data and only reads 32 bits
at a time. Using AR_GETWORD when time tagging is enabled results in
alternately reading data and time tag.
See AR_SETCHPARMS for a superior replacement for this function.
ARS_NORMAL Success.
ARS_INVBOARD Board is not initialized.
ARS_INVARG Invalid flag argument.
ARS_BOARD_MUTEX Failed to acquire/release the board lock.
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