Civil Engineering Reference
In-Depth Information
Fig. 3.6
Transmission of messages
mated routing by hardware (diagnostic and mirroring function). There are 16 trans-
mit message buffers available for each channel, and these are used and shared for all
these methods of sending messages. By means of sharing, all four sending methods
can be enabled at the same time for a channel. Thus, by sharing a channel between
several software applications, each application can use its favourite method. The
priority of transmission is evaluated on message-buffer level; this means that all
four methods of sending are in competition with each other according to the priority
rules, but every method may have its internal rules as well.
Figure
3.6
shows an example of a valid usage of the message buffers and how
they can be shared among the different sending methods.
3.3.3.1
Sending from Message Buffers
Every message buffer that has not been assigned to a transmit (TX) queue, a FIFO
or to automated GW routing can be used in this way. When sending from a message
buffer, this single message competes in priority with the remaining 15 message buf-
fers. The message buffer stores all the information required to generate a valid and
complete frame on the CAN bus.
In addition, there is a flag to enable the generation of an entry in the THL after
successful transmission, and there is an optional pointer value (usable as
AUTOSAR
HTH
), which will appear in the THL, too. This allows tracing and defined process-
ing of transmit objects.
3.3.3.2
Sending from Transmit Queues
Several message buffers can be grouped to form a
transmit queue
, always start-
ing with the uppermost buffer. Within this type of transmit queue, software simply
writes all its messages into one single message buffer (the uppermost one), and the
