AN2283 Freescale Semiconductor / Motorola, AN2283 Datasheet - Page 16

• Manufacturer Part Number: AN2283
• Description: Scalable Controller Area Network (MSCAN)
• Manufacturer: Freescale Semiconductor / Motorola

AN2283/D
Receive Structure Overview
16
Motorola Scalable Controller Area Network (MSCAN) Interrupts
As seen in
four separate scenarios:
The transmit interrupt routine may need to be modified to support the abort
capability in the MSCAN. For example, when a transmit empty buffer is
detected the service routine needs to signal the network/transport software
layers if the transmission completed successfully or the message was aborted.
One method is to issue a completion code to a transmit status routine
To understand the receive process, the first topic to cover is the receive
structure on the MSCAN. The MSCAN receive structure consists of a two-stage
input FIFO (First In First Out) buffer structure. The MSCAN validates the
received message and if no errors are detected, the message then goes
through a hardware filtering process of the identifier field to determine whether
to save the message in the receive FIFO or discard it.
The MSCAN’s two receive buffers are alternately mapped into a single location
in the memory map. The received messages are stored in a two-stage input
FIFO buffer structure:
Both the RxFG and RxBG buffers have a 13-byte data structure similar to the
transmit buffer. See
1. When the message in the buffer is not undergoing transmission on the
2. When the message in the buffer is undergoing transmission on the bus
•
•
Freescale Semiconductor, Inc.
For More Information On This Product,
bus the abort is granted immediately, ABTAKx = 1.
the MSCAN waits until the transmission completes. Transmission can
complete due to:
a.
b.
c.
The Background Receive Buffer (RxBG) is exclusively accessible by the
MSCAN
The Foreground Receive Buffer (RxFG) is accessible by the CPU
Figure
Loss of arbitration — the message is aborted and ABTAK = 1 (Abort
Acknowledged)
Transmission ends with errors — the message is aborted and
ABTAK = 1 (Abort Acknowledged)
Transmission is complete with no errors — in this case, there is
nothing to abort because the MSCAN tried to abort a now empty
buffer, so ABTAKx = 0 (Abort Not Acknowledged)
Go to: www.freescale.com
11, when there is an abort request for a message there are
Figure
12.
MOTOROLA