[PATCH] spec/cpukit: Omit Cortex-M from libdebugger build

[Chris Johns]

On 18/8/2023 7:01 am, Kinsey Moore wrote:
> On Thu, Aug 17, 2023 at 7:11 AM Kinsey Moore <kinsey.moore at oarcorp.com
> <mailto:kinsey.moore at oarcorp.com>> wrote:
> 
>     On Wed, Aug 16, 2023 at 9:42 PM Chris Johns <chrisj at rtems.org
>     <mailto:chrisj at rtems.org>> wrote:
> 
>         On 17/8/2023 6:30 am, Kinsey Moore wrote:
>         > The current ARM support in libdebugger does not cover Cortex-M series
>         > cores since it requires support for CP14 system register accessor
>         > instructions. Cortex-M series cores support debug monitor mode, but its
>         > configuration is accessed by memory mapped registers instead of using
>         > CP14. This omits building libdebugger from BSPs that use a cortex-m ABI
>         > flag.
> 
>         The ARM libdebugger has support to use memory mapped registers. It is
>         determined
>          by the ROM and then rtems_debugger_arm_debug_registers. I think the code
>         currently assume CP14 instructions but I think that could be made
>         conditional
>         where needed?
> 
>         Are these builds of Cortex-M processors able to support libdebugger?
> 
>         I have been rejecting changes like this unless there is a reason it
>         cannot be
>         made to work. Are there reasons it cannot be made to work?
> 
> 
>     As to my current understanding, I believe that the Cortex-M3/4/7 cores can
>     support libdebugger via their exclusive monitor mode. I'll see if I can work
>     around the CP14 issues instead.
> 
> 
> Reading into the relevant Architecture and Technical reference manuals, the ROM
> tables in the Cortex-M cores do not expose information about the debug and data
> watchpoint blocks. It looks like all the breakpoint (0xE0002000) and watchpoint
> (0xE0001000) controls are the same IP at the same address across the Cortex-M
> line, but are in no way compatible with the CP14-based breakpoint and watchpoint
> blocks in the Cortex-A/R lines of cores. The Cortex-M cores require a nearly
> unrelated libdebugger implementation.

Thanks for this and looking into it. I am fine with the change now we understand
it is not compatible. It sounds like a new back end would be cleaner for both
types of devices.

The patch is approved.

Chris