ARM Architecture Reference Manual ARMv7-A and ARMv7-R edition

Debug Events
Note
v6 Debug does not support IVA mismatch breakpoints.
v6.1 Debug and v6 Debug do not support address range masks on breakpoints.
IVA comparison programming examples
In all Debug architecture versions, a debugger must configure the BRP so that it matches on all bytes of the
first unit of the instruction, otherwise the generation of Breakpoint debug events is UNPREDICTABLE.
Before ARMv6T2, on a processor that implements the Thumb instruction set and can take an exception
between the two halfwords of a Thumb BL or BLX (immediate) instruction, a debugger must treat the two
halfwords as separate instructions, and set breakpoints on both halfwords. This might require two BRPs.
Note
To ensure compatibility across ARMv6 implementations, a debugger can always treat BL or BLX
(immediate) as two instructions when debugging code on an ARMv6 processor before ARMv6T2.
The examples that follow include setting breakpoints on ThumbEE instructions. These are supported
only in ARMv7.
For example, if BRPn and BRPm are two breakpoint register pairs, then:
On any ARMv6 or ARMv7 processor:
— To breakpoint on a Java bytecode at address 0x8001, the debugger must set DBGBVRn to
0x8000 and DBGBCRn[8:5] to 0b0010.
— To breakpoint on a 16-bit Thumb or ThumbEE instruction starting at address 0x8002, a
debugger must set DBGBVRn to 0x8000 and DBGBCRn[8:5] to 0b1100.
— To breakpoint on an ARM instruction starting at address 0x8004, a debugger must set
DBGBVRn to 0x8004 and DBGBCRn[8:5] to 0b1111.
On an ARMv7 or ARMv6T2 processor, a debugger sets breakpoints on a 32-bit Thumb instruction,
or on a 16-bit or a 32-bit ThumbEE instruction, in exactly the same way as on a 16-bit Thumb
instruction. For example:
— To breakpoint on a 16-bit or a 32-bit Thumb or ThumbEE instruction starting at address
0x8000, the debugger must set DBGBVRn to 0x8000 and DBGBCRn[8:5] to 0b0011. These are
the settings for breakpointing on any Thumb or ThumbEE instruction, including BL and BLX
(immediate).
On an ARMv6 or ARMv6K processor:
— To breakpoint on a Thumb BL or BLX instruction at address 0x8000, a debugger must set
DBGBVRn to 0x8000, and DBGBCRn[8:5] to 0b1111.
— To breakpoint on a Thumb BL or BLX instruction at address 0x8002, a debugger must set
DBGBVRn to 0x8000, DBGBVRm to 0x8004, DBGBCRn[8:5] to 0b1100, and
DBGBCRm[8:5] to 0b0011.
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