Freescale Semiconductor PowerQUICC MPC870, Reference Manual

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System Development and Debugging
MPC885 PowerQUICC Family Reference Manual, Rev. 2
53-14 Freescale Semiconductor
53.2.3.4 Trap Enable Programming
The trap enable bits can be programmed by regular software (only if MSR[PR] = 0) using the mtspr
instruction or on the fly using the special development port interface. See
Section 53.3.2.4, “Development
Port Serial Communications–Trap Enable Mode.” The value used by the breakpoint generation logic is the
bit-wise OR of the software trap enable bits written using the mtspr instruction, and the development port
trap enable bits that are serially shifted using the development port. The software trap enable bits and
development port trap enable bits can be read from ICTRL and the LCTRL2 using the mtspr instruction.
Table 53-20 and Table 53-22 show the exact bit placement.
53.2.4 Operation Details
The following sections describe various operating details of watchpoint and breakpoint.
53.2.4.1 Restrictions
The same watchpoint can be detected more than once during execution of an instruction. For example, a
load/store watchpoint can be detected on more than one transfer when executing load/store multiple/string
instructions or a load/store watchpoint can be detected on more than one byte in byte mode. In such cases
only one watchpoint of a given type is reported for the instruction. Similarly, only one watchpoint of the
same type can be counted for a single instruction. Watchpoint events are reported when the instruction that
caused the event retires; because more than one instruction can retire in a single clock, ensuing events may
be reported in the same clock. Moreover, an event detected on more than one instruction (tight loops or
range detection) can only be reported once. Internal counters count correctly in these cases.
53.2.4.2 Byte and Half Word Working Modes
The user can use watchpoints and breakpoints to detect matches on bytes and half words when the byte/half
word is accessed in a load/store instruction of larger data widths. For example, when loading a table of
bytes using a series of load word instructions. To use this feature in word mode, write the required match
value to the correct half word of the data comparator and the mask in the L-data comparator. To break on
bytes, the byte mask for each L-comparator and the bytes to be matched must be written in the data
comparator.
Because bytes and half words can be accessed using a larger data width instruction, the user cannot predict
the exact value of the L-address lines when the requested byte/half-word is accessed. If the matched byte
is byte 2 of the word and accessed using a load word instruction, the L-address value will be of the word
(byte 0). Therefore, the core masks the two lsbs of the L-address comparators for word accesses and the
lsb for half-word accesses. Address range is supported only when aligned according to access size.
53.2.4.2.1 Examples
The following examples show programming options for several search criteria:
• Example 1
Looking for:
Data size: Byte.