MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
19-64
Freescale Semiconductor
NOTE
When a lower priority CFIFO is served first because a higher priority
CFIFO cannot send its commands due to a full external command buffer,
there is a possibility that command transfers from the lower priority CFIFO
will be interrupted and the CFIFO will become non-coherent, when the
higher priority CFIFO again becomes ready to send commands. Whether the
lower priority CFIFO becomes non-coherent or not depends on the rate at
which commands on the external ADCs are executed, on the rate at which
commands are transmitted to the external command buffers, and on the
depth of those buffers.
After a serial transmission is started, the submodule monitors triggered CFIFOs and manages the abort of
serial transmissions. In case a null message is being transmitted, the serial transmission is aborted when
all of the following conditions are met:
•
A not-underflowing CFIFO in the TRIGGERED state has commands bound for an external
command buffer that is not full, and it is the highest priority CFIFO sending commands to an
external buffer that is not full.
•
The ABORT_ST bit of the command to be transmitted is asserted.
•
The 26th bit of the currently transmitting null message has not being shifted out.
The command from the CFIFO is then written into eQADC SSI transmit buffer, allowing for a new serial
transmission to initiate.
In case a command is being transmitted, the serial transmission is aborted when all following conditions
are met:
•
CFIFO0 is in the TRIGGERED state, is not underflowing, and its current command is bound for
an external command buffer that is not full.
•
The ABORT_ST bit of the command to be transmitted is asserted.
•
The 26th bit of the currently transmitting command has not being shifted out.
The command from CFIFO0 is then written into eQADC SSI transmit buffer, allowing for a new serial
transmission to initiate.
NOTE
The aborted command is not popped from the preempted CFIFO and will be
retransmitted as soon as its CFIFO becomes the highest priority CFIFO
sending commands to an unfilled external command buffer.
After a serial transmission is completed, the eQADC prioritizes the CFIFOs and schedules a command or
a null message to be sent in the next serial transmission. After the data for the next transmission has been
defined and scheduled, the eQADC can, under certain conditions, stretch the SDS negation time in order
to allow the schedule of new data for that transmission. This occurs when the eQADC acknowledges that
the status of a higher-priority CFIFO has changed to the TRIGGERED state and attempts to schedule that
CFIFO command before SDS is asserted. Only commands of CFIFOs that have the ABORT_ST bit
asserted can be scheduled in this manner. Under such conditions:
1. A CFIFO0 command is scheduled for the next transmission independently of the type of data that
was previously scheduled. The time during which SDS is negated is stretched in order to allow the
eQADC to load the CFIFO0 command and start its transmission.
Summary of Contents for MPC5553
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