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18-12
MPC801 USER’S MANUAL
MOTOROLA
18
Instructions with Instruction Breakpoints Are Not Executed. The Machine Branches To
the Breakpoint Exception Routine Before it Executes the Instruction.
Instructions with Load/Store Breakpoints are Executed. The Machine Branches To the
Breakpoint Exception Routine After it Executes the Instruction. The Address of the
Access is Placed In the Breakpoint Address Register.
Load/Store Multiple and String Instructions with Load/Store Breakpoints First Finish
Execution and Then the Machine Branches to the Breakpoint Exception Routine.
Load/Store Data Compare is Made On the Load/Store, After Swap in Store Accesses
and Before Swap in Load Accesses.
Internal Breakpoints Operate in Masked or Nonmasked Mode.
Both “go to x” and “continue” Working Modes are Supported for Instruction Breakpoints.
18.2.1.2 RESTRICTIONS.
more than once during the execution of a single instruction. For example, a load/store
watchpoint detected on more than one transfer when executing load/store multiple/string or
a load/store watchpoint detected on more than one byte when working in byte mode. In
these cases, only one watchpoint of the same type is reported for a single instruction.
Similarly, only one watchpoint of the same type can be counted in the counters for a single
instruction. Since watchpoint events are reported when the instruction that caused the event
retires ensuing events can be reported in the same clock. Moreover, if the same event is
detected on more than one instruction can just be reported once. The internal counters
count correctly in these cases.
There are times when the same watchpoint can be detected
18.2.1.3 BYTE AND HALF-WORD WORKING MODES.
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, the required
match value should be written to the correct half-word of the data comparator and to the
mask in the L-data comparator. If you prefer to break on bytes, the byte mask for each
L-comparator and the bytes to be matched must be written in the data comparator.
You can use watchpoints and
Since bytes and half-words can be accessed using a larger data width instruction, it is
impossible for you to 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 is accessed using a load
word instruction, the L-address value will be of the word (byte 0). Therefore, the core masks
the two least-significant bits of the L-address comparators whenever a word access is
performed and the least-significant bits whenever a half-word access is performed. Address
range is only supported when aligned according to the access size.