be processed every 11.5 cycles (4 + (4+5)/2 + 3). This is the time from Cycle 4 to Cycle x
+5. The resulting peak request rate, as a function of the system frequency, is shown in the
following table.
Table 12-6. eDMA peak request rate (MReq/sec)
System frequency (MHz)
Request rate
with zero wait states
Request rate
with wait states
48.0
5.3
4.2
66.6
7.4
5.8
83.3
9.2
7.2
100.0
11.1
8.7
133.3
14.8
11.6
150.0
16.6
13.0
A general formula to compute the peak request rate with overlapping requests is:
PEAKreq = freq / [ entry + (1 + read_ws) + (1 + write_ws) + exit ]
where:
Table 12-7. Peak request formula operands
Operand
Description
PEAKreq
Peak request rate
freq
System frequency
entry
Channel startup (4 cycles)
read_ws
Wait states seen during the system bus read data phase
write_ws
Wait states seen during the system bus write data phase
exit
Channel shutdown (3 cycles)
12.4.4.3 eDMA performance example
Consider a system with the following characteristics:
• Internal SRAM can be accessed with one wait-state when viewed from the system
bus data phase
• All internal peripheral bus reads require two wait-states, and internal peripheral bus
writes three wait-states viewed from the system bus data phase
• System operates at 150 MHz
For an SRAM to internal peripheral bus transfer,
Functional description
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