stmhal: Add pyb.fault_debug() function, to control hard-fault behaviour.

This new function controls what happens on a hard-fault:
- debugging disabled: board will do a reset
- debugging enabled: board will print registers and stack and flash LEDs

The default is disabled, ie to do a reset.  This is different to previous
behaviour which flashed the LEDs and waited indefinitely.

1 files changed, 13 insertions, 0 deletions

diff --git a/docs/library/pyb.rst b/docs/library/pyb.rst
index 910b2f45b4..9c4933808a 100644
--- a/docs/library/pyb.rst
+++ b/docs/library/pyb.rst
@@ -80,6 +80,19 @@ Reset related functions
 
    Activate the bootloader without BOOT\* pins.
 
+.. function:: fault_debug(value)
+
+   Enable or disable hard-fault debugging.  A hard-fault is when there is a fatal
+   error in the underlying system, like an invalid memory access.
+
+   If the `value` argument is `False` then the board will automatically reset if
+   there is a hard fault.
+
+   If `value` is `True` then, when the board has a hard fault, it will print the
+   registers and the stack trace, and then cycle the LEDs indefinitely.
+
+   The default value is disabled, i.e. to automatically reset.
+
 Interrupt related functions
 ---------------------------