NXP Semiconductors MPC5777C - Timestamp Generation; Timeout Counter

3.5.2 Timestamp Generation
For timestamp generation the M_CAN supplies a 16-bit wrap-around counter. A
prescaler TSCC[TCP] can be configured to clock the counter in multiples of CAN bit
times (1…16). The counter is readable via TSCV[TSC]. A write access to register TSCV
resets the counter to zero. When the timestamp counter wraps around interrupt flag
IR[TSW] is set.
On start of frame reception / transmission the counter value is captured and stored into
the timestamp section of an Rx Buffer / Rx FIFO (RXTS[15:0]) or Tx Event FIFO
(TXTS[15:0]) element.
3.5.3 Timeout Counter
To signal timeout conditions for Rx FIFO 0, Rx FIFO 1, and the Tx Event FIFO the
M_CAN supplies a 16-bit Timeout Counter. It operates as down-counter and uses the
same prescaler controlled by TSCC[TCP] as the Timestamp Counter. The Timeout
Counter is configured via register TOCC. The actual counter value can be read from
TOCV[TOC]. The Timeout Counter can only be started while CCCR[INIT] = 0. It is
stopped when CCCR[INIT] = 1, e.g. when the M_CAN enters Bus_Off state.
The operation mode is selected by TOCC[TOS]. When operating in Continuous mode,
the counter starts when CCCR[INIT] is reset. A write to TOCV presets the counter to the
value configured by TOCC[TOP] and continues down-counting.
When the Timeout Counter is controlled by one of the FIFOs, an empty FIFO presets the
counter to the value configured by TOCC[TOP]. Down-counting is started when the first
FIFO element is stored. Writing to TOCV has no effect.
When the counter reaches zero, interrupt flag IR[TOO] is set. In Continuous Mode, the
counter is immediately restarted at TOCC[TOP].
Note
The clock signal for the Timeout Counter is derived from the
CAN Core's sample point signal. Therefore the point in time
where the Timeout Counter is decremented may vary due to the
synchronization / re-synchronization mechanism of the CAN
Core. If the baud rate switch feature in CAN FD is used, the
timeout counter is clocked differently in arbitration and data
field.
Chapter 3 Modular CAN (M_CAN)
MPC5777C Reference Manual Addendum, Rev. 1, 12/2015
Freescale Semiconductor, Inc. 97