MOTOROLA
Chapter 19. Communications Processor
19-9
Part V. The Communications Processor Module
19.5.3.2 CP Command Execution Latency
The worst-case command execution latency for the CP is 120 clocks, while the typical
command execution latency is about 40 clocks.
19.6 Dual-Port RAM
The CPM has 5 Kbytes of static RAM conÞgured as dual-port memory, shown in
Figure 19-4.
Figure 19-4. Dual-Port RAM Block Diagram
The dual-port RAM consists of 4 Kbytes of system RAM and 1 Kbyte of parameter RAM
and is used for the following:
¥
Storing parameters associated with the SCCs, SMCs, SPI, I
2
C, and IDMAs (in
parameter RAM only)
¥
Storing the BDs (in any unused dual-port RAM area)
¥
Storing buffers (in any unused dual-port RAM area or external memory)
¥
Storing Motorola-supplied microcode for the CP (in system RAM only)
¥
Scratchpad area for user software (in any unused dual-port RAM area)
The dual-port RAM can be accessed either by the CP or by one of two internal U-bus
mastersÑthe PowerPC core or an SDMA channel. The core and the SDMA channels
access the dual-port RAM in two clocks, while the CP takes only one clock. For
simultaneous accesses with at least one write operation, the CP is delayed by one clock.
Address
Selectors
Data
Selectors
U-Bus Addr
CP
m
CodeInstr Addr
CP Data Addr
U-Bus Addr
CP Data Addr
CP
m
Code Instr
U-Bus Data
CP Data
Shaded area is system RAM. Note that in this Þgure, the area is not contiguous memory. For an accurate
representation of the physical implementation, see Figure 19-6.
Address
Selectors
Data
Selectors
512 Bytes
BD/Buffers/
m
Code
512 Bytes
BD/Buffers/
m
Code
512 Bytes
BD/Buffers/
m
Code
512 Bytes
BD/Buffers/
m
Code
512 Bytes
BD/Buffers/
m
Code
1,536 Bytes
BD/Buffers
1,024 Bytes
Parameter RAM
Dual-port RAM
Содержание MPC860 PowerQUICC
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