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TRACING AND DEBUGGING
Hardware breakpoint registers may be armed or disarmed. When the registers are armed, hardware
breakpoints can generate an architectural trace fault. When the registers are disarmed, no action
occurs, and execution continues normally. Since instructions are always word aligned, the two
low-order bits of the IPBx registers act as control bits. Control bits for the DABx registers reside in
the Breakpoint Control (BPCON) registers. BPCON enables the data address breakpoint registers,
and sets the specific modes of these registers. Hardware breakpoints are globally enabled by the
process controls trace enable bit (PC.te).
The IPBx, DABx, and BPCON registers may be accessed using normal load and store instructions
(except for loads from IPBx register). The application must be in supervisor mode for a legal
access to occur. See
Section 3.3, MEMORY-MAPPED CONTROL REGISTERS (pg. 3-6)
for
more information on the address for each register.
Applications must request modification rights to the hardware breakpoint resources, before
attempting to modify these resources. Rights are requested by executing the
instruction, as
sysctl
described in the following section.
9.2.7.3
Requesting Modification Rights to Hardware Breakpoint Resources
Application code must always first request and acquire modification rights to the hardware
breakpoint resources before any attempt is made to modify them. This mechanism is employed to
eliminate simultaneous usage of breakpoint resources by emulation tools and application code. An
emulation tool exercises supervisor control over breakpoint resource allocation. If the emulator
retains control of breakpoint resources, none are available for application code. If an emulation
tool is not being used in conjunction with the device, modification rights to breakpoint resources
will be granted to the application. The emulation tool may relinquish control of breakpoint
resources to the application.
If the application attempts to modify the breakpoint or breakpoint control (BPCON) registers
without first obtaining rights, an OPERATION.UNIMPLEMENTED fault will be generated. In
this case, the breakpoint resource will not be modified, whether accessed through a
sysctl
instruction or as a memory-mapped register.
9-6
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