SH7058 Datasheet, PDF (641/1130 Pages) Renesas Technology Corp – Renesas SuperHTM RISC engine

• Internal Arbitration for Transmission
Figure 16.9 explains how the HCAN manages to schedule transmit-requested messages in the
correct order based on the CAN ID. “Internal arbitration” picks up the highest priority message
among transmit-requested messages.
CAN bus
state
Frame-1
Frame-2
Frame-3
Bus idle SOF Message EOF Interm SOF Message EOF Interm SOF
Tx=arbitation for Tx=arbitation for
HCAN
frame-1
frame-2
Rx matching
scheduler state
Scheduler
start point
Tx=arbitation for
Tx=arbitation for
frame-3
Rx matching frame-4
TXPR/TXCR/
Error/Arbitation-lost
set point
1-1
2-1
2-2 3-1 3-2
3-3 3-4
Interm: Intermission Field
SOF: Start Of Frame
EOF: End Of Frame
Message: Arbitration + control + data + CRC + Ack field
Figure 16.9 Internal Arbitration for Transmission
The HCAN scheduler, which runs internal arbitration, has 2 states – Tx arbitration state and Rx
matching state. The HCAN scheduler is in the Rx matching state if the CAN bus is in the EOF or
intermission cycles, or otherwise is in the Tx arbitration state. When a transmit request or transmit
abort request is made in the Tx arbitration state, the internal arbitration starts running immediately.
When a transmit request or transmit abort request is made in the Rx matching state, the internal
arbitration waits until the Rx matching state (i.e. intermission field) is finished, and then starts
running as soon as the HCAN scheduler state becomes the Tx arbitration.
There are 5 sources that can run internal arbitration, which are:
• TXPR is set
• TXCR is set (if TXCR is set for the message currently under transmission, the HCAN does not
stop the transmission but completes. If the message loses the bus arbitration or causes an error
on the bus, the HCAN will cancel the transmit request.)
• Error occurs on the CAN bus
• Message under transmission loses the arbitration on the CAN bus
• Mailbox with the setting MBC = 001 receives a remote frame
Rev. 3.0, 09/04, page 600 of 1086