Техническая Спецификация для Atmel Evaluation Kit AT91SAM9X25-EK AT91SAM9X25-EK

919

SAM9X25 [DATASHEET]

11054E–ATARM–10-Mar-2014

Using the free running 16-bit internal timer, the CAN controller can be set in one of the two following timing modes:



Timestamping Mode: The value of the internal timer is captured at each Start Of Frame or each End Of Frame.



Time Triggered Mode: The mailbox transfer operation is triggered when the internal timer reaches the mailbox 
trigger.

Timestamping Mode is enabled by clearing the TTM bit in the CAN_MR register. Time Triggered Mode is enabled by 
setting the TTM bit in the CAN_MR register.

Each mailbox has its own timestamp value. Each time a message is sent or received by a mailbox, the 16-bit value 
MTIMESTAMP of the CAN_TIMESTP register is transferred to the LSB bits of the CAN_MSRx register. The value read in 
the CAN_MSRx register corresponds to the internal timer value at the Start Of Frame or the End Of Frame of the 
message handled by the mailbox. 

In Time Triggered Mode, basic cycles can be split into several time windows. A basic cycle starts with a reference 
message. Each time a window is defined from the reference message, a transmit operation should occur within a pre-
defined time window. A mailbox must not win the arbitration in a previous time window, and it must not be retried if the 
arbitration is lost in the time window.

TEOF 

(CAN_MR)

MTIMESTAMP

(CAN_MSRx)

CAN_TIM

CAN BUS

MTIMESTAMP

(CAN_MSRy)

Message 1

Message 2

Start of Frame

TIMESTAMP

(CAN_TSTP)

End of Frame

Timestamp 1

Timestamp 1

Timestamp 2

Timestamp 2

Reference

Message

Reference

Message

Global Time

Time Cycle

Time Windows for Messages