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ColdFire Core
3-27
Freescale Semiconductor
A fault detected with the destination memory write is reported during the second cycle. At this point,
operations performed in the first cycle are complete, so if the destination write takes any type of access
error, Ay is updated. After the access error handler executes and the faulting instruction restarts, the
processor’s operation would be incorrect (without the special register recovery hardware) because the
source-address register has an incorrect (post-incremented) value.
To recover the original state of the programming model for all instructions, the Version 4 ColdFire core
adds the needed hardware to support full-register recovery. This hardware allows program-visible registers
to be restored to their original state for multi-cycle instructions so that the instruction restart mechanism
is supported. Memory-to-memory moves and move-multiple loads are representative of the complex
instructions needing the special recovery support.
Recall the IFP and OEP are decoupled by a FIFO instruction buffer. In the V4 ColdFire IFP, each buffer
entry includes 48 bits of instruction data fetched from memory and 64 bits of early decode and branch
prediction information. This datapath also includes IFP fault-status information. Therefore, every IFP
access can be tagged if an instruction fetch terminates with an error acknowledge. IFP access errors are
recognized after the buffered instruction enters the OEP.
NOTE
For access errors signaled on instruction prefetches, an access error
exception is generated only if instruction execution is attempted. If an
instruction fetch access error exception is generated and the FS field
indicates the fault occurred on an extension word, it may be necessary for
the exception PC to be rounded-up to the next page address to determine the
faulting instruction fetch address.
3.3.5
Instruction Execution Timing
This section presents processor instruction execution times in terms of processor-core clock cycles. The
number of operand references for each instruction is enclosed in parentheses following the number of
processor clock cycles. Each timing entry is presented as C(R/W) where:
•
C
is the number of processor clock cycles, including all applicable operand fetches and writes, and
all internal core cycles required to complete the instruction execution.
•
R/W is the number of operand reads (R) and writes (W) required by the instruction. An operation
performing a read-modify-write function is denoted as (1/1).
This section includes the assumptions concerning the timing values and the execution time details.
Table 3-11. OEP EX Cycle Operations
EX Cycle
Operations
1
Read source operand from memory @ (Ay), update Ay, new Ay = old Ay + 4
2
Write operand into destination memory @ (Ax), update Ax, new Ax = old Ax + 4, update CCR
Summary of Contents for MCF54455
Page 33: ...xxviii Freescale Semiconductor ...
Page 67: ...Freescale Semiconductor 1 ...
Page 125: ...Freescale Semiconductor 1 ...
Page 145: ...Enhanced Multiply Accumulate Unit EMAC 5 21 Freescale Semiconductor ...
Page 173: ...Cache 6 28 Freescale Semiconductor ...
Page 179: ...Static RAM SRAM 7 6 Freescale Semiconductor ...
Page 207: ...Power Management 9 16 Freescale Semiconductor ...
Page 323: ...Reset Controller Module 13 8 Freescale Semiconductor ...
Page 389: ...Pin Multiplexing and Control 16 44 Freescale Semiconductor ...
Page 575: ...PCI Bus Controller 22 58 Freescale Semiconductor ...
Page 600: ...Advanced Technology Attachment ATA Freescale Semiconductor 23 25 ...
Page 601: ...Freescale Semiconductor 1 ...
Page 842: ...I2 C Interface Freescale Semiconductor 33 16 ...
Page 843: ...Freescale Semiconductor 1 ...
Page 921: ...Revision History A 6 Freescale Semiconductor ...