Enhanced Queued Analog-to-Digital Converter (eQADC)
MPC5565 Microcontroller Reference Manual, Rev. 1.0
Freescale Semiconductor
18-65
NOTE
When a higher priority CFIFO cannot send commands due to a full external
command buffer, a lower priority CFIFO is served. When the higher priority
CFIFO is ready to send commands, an interrupt to the command transfers
from the lower priority CFIFO can result in CFIFO incoherence. Whether
the lower priority CFIFO becomes non-coherent depends on the following:
•
rate at which commands on the external ADCs are executed
•
rate at which commands are transmitted to the external command buffers
•
depth of those buffers.
After a serial transmission starts, the submodule monitors triggered CFIFOs and manages the abort of the
serial transmissions. If a null message is 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 is not 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 pre-empted CFIFO, but is
retransmitted as soon as it’s 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 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
Содержание MPC5565
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