One of the more interesting things about the ARM Cortex-M series is that debugging is "built in" to the CPU core on all licensed processors. No hacks required. Something that I'm sure x86 machines would have had, if transistors has been as cheap then as they are now. Of course early on Intel made even more margin on versions of the processor used for doing in circuit emulation by 'bonding out' to an unused pad access to internal trace registers.
I'm pretty certain that Visual Studio uses those for "memory breakpoints", and that GDB uses those for "hardware watchpoints", to use their respective nomenclature. And these are very handy at times.
