Architecture
622
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Enhanced Direct Memory Access (EDMA3) Controller
17.2.14.3 Throttling the Read Command Rate in a Transfer Controller
By default, the transfer controller issues reads as fast as possible. In some cases, the reads issued by the
EDMA3TCC could fill the available command buffering for a slave, delaying other (potentially higher
priority) masters from successfully submitting commands to that slave. The rate at which read commands
are issued by the EDMA3TC is controlled by the read command rate register (RDRATE), and this can be
used to throttle the rate at which the commands are issued from the TC read interface. RDRATE defines
the number of cycles that the EDMA3TC read controller waits before issuing subsequent commands for a
given TR, thus minimizing the chance of the EDMA3TC consuming all available slave resources. The
RDRATE value should be set to a relatively small value (or kept at default, which implies issuing read
requests as fast as possible) if the transfer controller is targeted for high-priority transfers and set to a high
value if the transfer controller is targeted for low-priority transfers. In contrast, the write Interface does not
have any performance turning knobs because writes always have an interval between commands as write
commands are submitted along with the associated write data.
17.2.15 EDMA3 Operating Frequency (Clock Control)
The EDMA3 channel controller and transfer controller are clocked from PLL controller 0 (PLLC0). For
details, see the
Phase-Locked Loop Controller (PLLC)
chapter.
17.2.16 Reset Considerations
A hardware reset resets the EDMA3 (EDMA3CC and EDMA3TC) and the EDMA3 configuration registers.
The PaRAM memory contents are undefined after device reset and you should not rely on parameters to
be reset to a known state. The PaRAM set must be initialized to a desired value before it is used.
17.2.17 Power Management
The EDMA3 (EDMA3CC and EDMA3TC) can be placed in reduced-power modes to conserve power
during periods of low activity. The power management of the peripheral is controlled by the device Power
and Sleep Controller (PSC). The PSC acts as a master controller for power management for all
peripherals on the device. For detailed information on power management procedures using the PSC, see
the
Power and Sleep Controller (PSC)
chapter.
The EDMA3 controller can be idled on receiving a clock stop request from the PSC. The requests to
EDMA3CC and EDMA3TC are separate. In general, you should verify that there are no pending activities
in the EDMA3 controller before issuing a clock stop request via PSC.
The EDMA3CC checks for the following conditions:
•
No pending DMA/QDMA events
•
No outstanding events in the event queues
•
Transfer request processing logic is not active
•
No completion requests outstanding (early or normal completion)
•
No configuration bus requests in progress
The first four conditions are software readable by the channel controller status register (CCSTAT) in the
EDMA3CC.
Similarly, from the EDMA3TC perspective, you should check that there are no outstanding TRs that are
getting processed and essentially the read/write controller is not busy processing a TR. The activity of
EDMA3TC logic is read in TCSTAT for each EDMA3TC.
It is generally recommended to first disable the EDMA3CC and then the EDMA3TC(s) to put the EDMA3
controller in reduced-power modes.
Additionally, when EDMA3 is involved in servicing a peripheral and it is required to power-down both the
peripheral and the EDMA, the recommended sequence is to first disable the peripheral, then disable the
DMA channel associated with the peripheral (clearing the EER bit for the channel), then disable the
EDMA3CC, and finally disable the EDMA3TC(s).