MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
Freescale Semiconductor
9-37
•
System operates at 150 MHz.
For an SRAM to slave transfer,
PEAKreq = 150 MHz / [ 4 + (1 + 1) + (1 + 3) + 3 ] cycles = 11.5 Mreq/sec
For an slave to SRAM transfer,
PEAKreq = 150 MHz / [ 4 + (1 + 2) + (1 + 1) + 3 ] cycles = 12.5 Mreq/sec
Assuming an even distribution of the two transfer types, the average peak request rate would be:
PEAKreq = (11.5 Mreq/sec + 12.5 Mreq/sec) / 2 = 12.0 Mreq/sec
The minimum number of cycles to perform a single read/write, zero wait states on the system bus, from a
cold start (where no channel is executing, eDMA is idle) are the following:
•
11 cycles for a software (TCD.START bit) request
•
12 cycles for a hardware (eDMA peripheral request signal) request
Two cycles account for the arbitration pipeline and one extra cycle on the hardware request resulting from
the internal registering of the eDMA peripheral request signals. For the peak request rate calculations
above, the arbitration and request registering is absorbed in or overlap the previous executing channel.
NOTE
When channel linking or scatter/gather is enabled, a two-cycle delay is
imposed on the next channel selection and startup. This allows the link
channel or the scatter/gather channel to be eligible and considered in the
arbitration pool for next channel selection.
9.5
Initialization / Application Information
9.5.1
eDMA Initialization
A typical initialization of the eDMA would have the following sequence:
1. Write the EDMA_CR if a configuration other than the default is desired.
2. Write the channel priority levels into the EDMA_CPR
n
registers if a configuration other than the
default is desired.
3. Enable error interrupts in the EDMA_EEIRL and/or EDMA_EEIRH registers if so desired.
4. Write the 32-byte TCD for each channel that may request service.
5. Enable any hardware service requests via the EDMA_ERQRH and/or EDMA_ERQRL registers.
6. Request channel service by either software (setting the TCD.START bit) or by hardware (slave
device asserting its eDMA peripheral request signal).
After any channel requests service, a channel is selected for execution based on the arbitration and priority
levels written into the programmer's model. The eDMA engine will read the entire TCD, including the
primary transfer control parameter shown in
, for the selected channel into its internal address
path module. As the TCD is being read, the first transfer is initiated on the system bus unless a
configuration error is detected. Transfers from the source (as defined by the source address, TCD.SADDR)
to the destination (as defined by the destination address, TCD.DADDR) continue until the specified
number of bytes (TCD.NBYTES) have been transferred. When the transfer is complete, the eDMA
engine's local TCD.SADDR, TCD.DADDR, and TCD.CITER are written back to the main TCD memory
and any minor loop channel linking is performed, if enabled. If the major loop is exhausted, further post
Summary of Contents for MPC5553
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