AVR32AP datasheet(88/181 Pages) ATMEL

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32001A–AVR32–06/06

AVR32

9.1.2.3

Transmit Queue

Trace and watchpoint messages are inserted into the Transmit Queue (TXQ) before being trans-

mitted on the AUX port. This provides some flexibility between the peak rate of trace message

generation and the average rate of message transmission on the AUX port.

9.1.2.4

Flow Control Unit

The Flow Control Unit (FCU) can bring the CPU into and out of Debug Mode, and control the

CPU operation in Debug Mode. The behavior is controlled by accessing OCD registers.

Debug Mode can be configured as OCD Mode or Monitor Mode. In OCD mode, The CPU

fetches instructions from the Debug Instruction Register. If the register is empty, the CPU is

halted. In Monitor Mode, the CPU fetches debug instructions from a monitor code in the program

memory, and the Debug Instruction Register is not used.

The FCU also handles single stepping by returning the CPU to normal mode, letting the CPU

fetch one instruction from the program memory, and then returning to Debug Mode on the fol-

lowing instruction.

9.1.2.5

Breakpoint modules

A number of instruction and data breakpoint modules can be configured for run-time monitoring

of the instruction fetches and data accesses by the CPU. The modules can report if the moni-

tored operation matches a predefined address, alternatively, also a data value. The modules

operate on virtual addresses.

A breakpoint will bring the CPU into Debug Mode. Watchpoints are reported to the debugger,

but does not affect CPU operation. A watchpoint can also be configured to start or stop data and

program trace.

The breakpoint modules can be combined to produce a watchpoint or breakpoint. Complex

breakpoint/watchpoint conditions are supported, e.g. trigger when a specific procedure writes a

certain variable with a specific value.

9.1.2.6

Program and Data Trace

The Program Trace Unit sends Branch Trace Messages to the debugger, which allows the pro-

gram flow to be reconstructed. To keep the amount of debug information low to save bandwidth,

only change of program flow are reported (such as unconditional branches, taken conditional

branches interrupts, exceptions, return operations, and load operations with PC as destination),

hence the term "branch tracing". Messages are typically relative to the previously transmitted

message, to be able to compress information as much as possible. Thus, the trace messages

are sent out in temporal order, and regularly, synchronization messages with uncompressed,

absolute addresses, are transmitted in case synchronization is lost.

The Data Trace Unit similarly traces data accesses, for read or write accesses, or both. Similar

relative address compression and synchronization schemes are used for Data Trace Messages.

Since new trace messages can be generated before the previous ones have been transmitted,

all trace messages are queued before being transmitted by the AUX interface. If the queue over-

flows, the CPU can be halted to avoid losing trace information, or an error message followed by

synchronization trace messages will be transmitted.

9.1.2.7

RTOS debug support

Applications developed on an RTOS platform places special requirements on the OCD controller

and the debug software. For high-level debugging, the user will want to see which process is

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