System Development and Debugging
MPC885 PowerQUICC Family Reference Manual, Rev. 2
53-2
Freescale Semiconductor
The information required to enable reconstruction of program trace includes:
•
A description of the last fetched instruction (stall, sequential, branch not taken, branch direct taken,
branch indirect taken, interrupt/exception taken).
•
The addresses of the targets of all indirect flow changes. Indirect flow changes include all branches
using the link and count registers as the target address, all interrupts/exceptions, and rfi and mtmsr
(because they may cause context switches).
•
The number of instructions canceled on each clock.
The following sections define how this information is generated and how it should be used to reconstruct
the program trace.
53.1.1
Program Trace Functional Description
To make the events that occur in the machine visible, a few dedicated pins are used. Also, a special bus
cycle attribute called program trace cycle is defined. The program trace cycle attribute is attached to all
fetch cycles resulting from indirect flow changes. When program trace recording is required, the user can
ensure these cycles are visible on the external bus.
The core can be forced to show all fetch cycles marked with the program trace cycle attribute either by
setting TECR[VSYNC] of the development port or by programming ISCT_SER in the instruction support
control register (ICTRL). For more information on VSYNC see
Section 53.3.2, “Development Port
Communication.”
Both states described here are subsequently referred to as VSYNC state.
The VSYNC state forces all fetch cycles marked with the program trace cycle attribute to be visible on the
external bus, even if their data is found in one of the internal devices. To enable the external hardware to
properly synchronize with the internal activity of the core, entering VSYNC state forces the machine to
synchronize and the first fetch after this synchronization to be marked as a program trace cycle and be seen
on the external bus.
In VSYNC state, fetch cycles marked with the program trace cycle attribute become visible on the external
bus. These cycles generate regular bus cycles when the instructions reside in an external device or generate
address-only cycles when instructions are in internal devices (I-cache and internal memory). In VSYNC
state, performance degrades because of the additional external bus cycles. However, this degradation is
very small.
Note that program trace functions are not available when operating the MPC885 in half-speed bus mode
(when SCCR[EBDF] = 0b01). The VFLS[0–1] signals are not valid in half-speed bus mode.
53.1.2
Instruction Fetch Show Cycle Control
Instruction fetch show cycles are controlled by ICTRL[ISCT_SER] and the state of VSYNC.
Table 53-1
defines the level of fetch show cycles generated by the core.
Summary of Contents for PowerQUICC MPC870
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