boards/common/cc26xx_cc13xx: Fix flashing with upstream OpenOCD

This adds a work around that allows flashing with upstream OpenOCD,
most of the time.

boards/common/cc26xx_cc13xx/Makefile.include

@@ -16,6 +16,13 @@ TTY_BOARD_FILTER := --model XDS110 --iface-num 0
 UNIFLASH_CONFIG ?= $(RIOTBOARD)/common/cc26xx_cc13xx/dist
 
 OPENOCD_DEBUG_ADAPTER ?= xds110
+# Work around a bug in the CC26xx / CC13xx that is triggered by 'reset halt'.
+# This results in the CC26xx / CC13xx being flash-able again, but it may race
+# against the target firmware installing IRQ handlers that may trigger while
+# the device is being flashed, which is bound to cause unpleasantness. But
+# flashing working fine most of the time is better than flashing working not
+# at all...
+OPENOCD_CMD_RESET_HALT ?= -c 'halt'
 
 ifneq (,$(filter cc13x0%,$(CPU_MODEL)))
   DEFAULT_OPENOCD_CONFIG := $(RIOTBASE)/boards/common/cc26xx_cc13xx/dist/openocd_cc13x0.cfg

cpu/cc26xx_cc13xx/doc.txt

@@ -68,11 +68,29 @@ that provides programming, flashing and debugging capabilities.
 
 It can either use proprietary Texas Instruments tools for programming, or OpenOCD.
 
-### Using OpenOCD
+### Using Upstream OpenOCD
 
-To use OpenOCD with the XDS110 you need to use the an special version of
-OpenOCD made by TI (upstream version is not _yet_ compatible). You can
-clone and compile it from source:
+OpenOCD is the default programmer and debugger. Hence, flashing can be done
+by navigating to the application directory and running:
+
+```
+make flash BOARD=<CC26xx-or-CC13xx-based-board>
+```
+
+@warning    A reliable and robust sequence to reset the CC26xx / CC13xx from
+            upstream OpenOCD is not yet implemented. As a result, OpenOCD will
+            halt the MCU for flashing without reset. This may result in IRQ
+            handlers being already set up and responding to IRQs that trigger
+            while flashing. Hence, flashing is likely not 100% reliable.
+
+@note       By default the XDS110 debug adapter is used, which is the debugger
+            TI integrates into is developments boards. This can be overwritten
+            by setting `OPENOCD_DEBUG_ADAPTER` to a different debugger.
+
+### Using TI's OpenOCD Fork
+
+TI maintains an outdated fork of OpenOCD that contains patches and special
+handling that have not upstreamed yet. It can be build using:
 
 ```
 # Clone into the openocd-ti folder
@@ -87,17 +105,25 @@ make
 sudo make install
 ```
 
-@note Sometimes OpenOCD may stop working when the firmware on the XDS110
-is updated (when using Uniflash, happens without user intervention). With that
-in mind, it's encouraged to either enable the ROM bootloader backdoor to enable
-serial programming or the installation of TI Uniflash as a fallback. See
-[Using Uniflash](#cc26xx_cc13xx_uniflash)
+@warning    Sometimes OpenOCD may stop working when the firmware on the XDS110
+            is updated (when using Uniflash, happens without user intervention).
+            With that in mind, it's encouraged to either enable the ROM
+            bootloader backdoor to enable serial programming or the
+            installation of TI Uniflash as a fallback. See
+            [Using Uniflash](#cc26xx_cc13xx_uniflash)
 
-#### Setting up the environment
+@note       With `OPENOCD_CMD_RESET_HALT="-c 'reset halt'"` the default reset
+            sequence can be restored. This may work with TI's OpenOCD fork.
 
-To flash a board using OpenOCD you can use do it so by setting the `PROGRAMMER`
-environment variable directly in the make command line or in your shell
-nitialization
+Otherwise, usage is identical with the upstream version of OpenOCD.
+
+### using J-Link
+
+By passing (or exporting) `PROGRAMMER=jlink` J-Link can be used to flash the
+board. This requires a J-Link compatible programmer / debugger. Since the
+XDS110 that TI's development boards use is not compatible, an external
+programmer has to be used. The upside is that flashing appears to be reliable
+with that.
 
 ### Using Uniflash