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Debug Module
Freescale Semiconductor
34-54
34.4.4.1
Begin Execution of Taken Branch (PST = 0x5)
PST is 0x5 when a taken branch is executed. For some opcodes, a branch target address may be displayed
on PSTDDATA depending on the CSR settings. CSR also controls the number of address bytes displayed,
which is indicated by the PST marker value immediately preceding the PSTDDATA nibble that begins the
data output.
Multiple byte DDATA values are displayed in least-to-most-significant order. The processor captures only
those target addresses associated with taken branches that use a variant addressing mode (RTE and RTS
instructions, JMP and JSR instructions using address register indirect or indexed addressing modes, and
all exception vectors).
The simplest example of a branch instruction using a variant address is the compiled code for a C language
case statement. Typically, the evaluation of this statement uses the variable of an expression as an index
into a table of offsets, where each offset points to a unique case within the structure. For such
change-of-flow operations, the ColdFire processor uses the debug pins to output the following sequence
of information on two successive processor clock cycles:
1. Use PSTDDATA (0x5) to identify that a taken branch is executed.
0x5
Begin execution of taken branch or SYNC_PC command issued. For some opcodes, a branch target
address may be displayed on PSTDDATA depending on the CSR settings. CSR also controls the number of
address bytes displayed, indicated by the PST marker value preceding the PSTDDATA nibble that begins
the data output. See
Section 34.4.4.1, “Begin Execution of Taken Branch (PST = 0x5)”
. Also indicates that
the SYNC_PC command has been issued.
0x6
Begin execution of instruction plus a taken branch. The processor completes execution of a taken
conditional branch instruction and simultaneously starts executing the target instruction. This is achieved
through branch folding.
0x7
Begin execution of return from exception (RTE) instruction.
0x8–
0xB
Indicates the number of bytes to be displayed on the PSTDDATA port on subsequent clock cycles. The value
is driven onto the PSTDDATA port one cycle before the data is displayed.
0x8 Begin 1-byte transfer on PSTDDATA.
0x9 Begin 2-byte transfer on PSTDDATA.
0xA Begin 3-byte transfer on PSTDDATA.
0xB Begin 4-byte transfer on PSTDDATA.
0xC
Normal exception processing. Exceptions that enter emulation mode (debug interrupt or optionally trace)
generate a different encoding, as described below. Because the 0xC encoding defines a multiple-cycle
mode, PSTDDATA outputs are driven with 0xC until exception processing completes.
0xD
Emulator mode exception processing.
Displayed during emulation mode (debug interrupt or optionally
trace). Because this encoding defines a multiple-cycle mode, PSTDDATA outputs are driven with 0xD until
exception processing completes.
0xE
A breakpoint state change causes this encoding to assert for one cycle only followed by the trigger status
value. If the processor stops waiting for an interrupt, the encoding is asserted for multiple cycles. See
Section 34.4.4.2, “Processor Stopped or Breakpoint State Change (PST = 0xE)
.”
0xFF
Processor is halted. Because this encoding defines a multiple-cycle mode, the PSTDDATA outputs display
0xF until the processor is restarted or reset. See
Table 34-30. Processor Status Encoding (continued)
PST[3:0]
Definition
Содержание MCF54455
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