mcf51ac256a Freescale Semiconductor, Inc, mcf51ac256a Datasheet - Page 553

• Manufacturer Part Number: mcf51ac256a
• Description: Mcf51ac Flexis
• Manufacturer: Freescale Semiconductor, Inc

The resulting PST/DDATA output stream, with the application program memory image, provides an
instruction-by-instruction dynamic trace of the execution path. For this device, the visibility bus optionally
supports this type of real-time trace as explained in
Visibility Bus Enabled (CSR[VBD] = 0].”
Even with the application of a PST trace buffer, problems associated with the PST bandwidth and
associated fill rate of the buffer remain. Given that there is one (or more) PST entry per instruction, the
PSTB would fill rapidly without some type of data compression.
Consider the following example to illustrate the PST compression algorithm. Most sequential instructions
generate a single PST = 1 value. Without compression, the execution of ten sequential instructions
generates a stream of ten PST = 1 values. With PST compression, the reporting of any PST = 1 value is
delayed so that consecutive PST = 1 values can be accumulated. When a PST ≠ 1 value is reported, the
maximum accumulation count is reached, or a debug data value is captured, a single accumulated PST
value is generated. Returning to the example with compression enabled, the execution of ten sequential
instructions generates a single PST value indicating ten sequential instructions have been executed.
This technique has proven to be effective at significantly reducing the average PST entries per instruction
and PST entries per machine cycle. The application of this compression technique makes the application
of a useful PST trace buffer for the V1 ColdFire core realizable. The resulting 5-bit PST definitions are
shown in
Freescale Semiconductor
PST[4:0]
— Captured operand creates the appropriate number of DDATA entries, each with 4 bits of data
0x00
0x01
0x02
0x03
0x04
0x05
0x06
0x07
Table
22-27.
Continue execution. Many instructions execute in one processor cycle. If an instruction requires more
processor clock cycles, subsequent clock cycles are indicated by driving PST with this encoding.
Begin execution of one instruction. For most instructions, this encoding signals the first processor clock
cycle of an instruction’s execution. Certain change-of-flow opcodes, plus the PULSE and WDDATA
instructions, generate different encodings.
Reserved
Entry into user-mode. Signaled after execution of the instruction that caused the ColdFire processor to
enter user mode.
Begin execution of PULSE and WDDATA instructions. PULSE defines triggers or markers for debug
and/or performance analysis. WDDATA lets the core write any operand (byte, word, or longword)
directly to the DDATA port, independent of debug module configuration. When WDDATA is executed, a
value of 0x04 is signaled on the PST port, followed by the appropriate marker, and then the data transfer
on the DDATA port. The number of captured data bytes depends on the WDDATA operand size.
Begin execution of taken branch or SYNC_PC BDM command. For some opcodes, a branch target
address may be displayed on DDATA depending on the CSR settings. CSR also controls the number of
address bytes displayed, indicated by the PST marker value preceding the DDATA nibble that begins
the data output. This encoding also indicates that the SYNC_PC command has been processed.
Reserved
Begin execution of return from exception (RTE) instruction.
Table 22-27. CF1 Debug Processor Status Encodings with VBus Disabled
MCF51AC256 ColdFire Integrated Microcontroller Reference Manual, Rev. 5
Section 22.4.3, “Real-Time Trace Support with the
Definition
Version 1 ColdFire Debug (CF1_DEBUG)
22-61