SH7760 Datasheet, PDF (865/1345 Pages) Renesas Technology Corp – SuperHTM RISC engine

• Internal Arbitration for Transmission
The following diagram explains how HCAN2 manages to schedule transmission-requested
messages in the correct order based on the CAN identifier. ‘Internal arbitration’ picks up
the highest priority message among messages transmitted-request messages.
CAN bus
Frame 1
Frame 2
Frame 3
Bus idle SOF Message EOF Interm SOF Message EOF Interm SOF
HCAN2
scheduler
Scheduler
start point
Tx arbitration Tx arbitration
for Frame 1 for Frame 2 Rx matching
TXPR/TXCR/
Error/arbitration _1-1
-lost set point
2-1
2-2 3-1 3-2
Tx arbitration
Tx arbitration
for Frame 3 Rx matching for Frame 4
3-4 3-3
1-1
:If CANTXPR bit is set during the CAN bus idle state, the internal arbitration starts operation
and transmission is started.
2-1 , 2-2 :If one of the five factors described above is generated in this period (during frame 2 Tx arbitration),
the internal arbitration is started and the next transmitted frame (frame 2) is scheduled.
3-1 , 3-2 :The internal arbitration is disabled in this period (during Rx matching). It is scheduled
at the SOF of the next frame (frame 2). If the message requested to be transmitted is in the
highest priority, transmission is provided in frame 3.
3-3 , 3-4 :Same as 2-1 , 2-2 .
Interm
SOF
EOF
Message
: Intermission field
: Start of frame
: End of frame
: Arbitration + Control + Data + CRC + ACK
Figure 22.7 Internal Arbitration for Transmission
The HCAN2 Scheduler, which runs internal arbitration, has two states, Tx Arbitration State and
Rx Matching State. HCAN2 Scheduler is in the Rx Matching State if the CAN bus is in the EOF
or Intermission cycle, or otherwise is in the Tx Arbitration State. When a transmission (or
transmission abortion) request is made in the Tx Arbitration State, the internal arbitration starts
immediately. When a transmission (or transmission abortion) 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 HCAN2 scheduler state becomes the ‘Tx arbitration state’.
There are 5 factors that can run internal arbitration, which are:
• CANTXPR is set.
Rev. 1.0, 02/03, page 815 of 1294