boards/frdm: use a more reliable reset_config

TODO THIS SHOULD BE TESTED AND JUSTIFIED

I checked the 'target/klx.cfg' and 'target/kx.cfg' and they both set
'reset_config srst_nogate' so re-add it in the common file.

Also enable 'connect_assert_srst' to allow flashing when the cpu does
not answer anymore.
I added the command DBG handling when using `connect_assert_srst`.

boards/common/frdm/Makefile.include

@@ -31,6 +31,10 @@ endif
 # Configuration for OpenOCD v0.10.0 and newer
 export OPENOCD_CONFIG ?= $(RIOTBOARD)/common/frdm/dist/openocd-$(CPU_FAMILY).cfg
 
+# call a 'reset halt' command before starting the debugger
+# it is required as `connect_assert_srst` is set
+export OPENOCD_DBG_START_CMD = -c 'reset halt'
+
 # Check the flash configuration field before flashing
 export PRE_FLASH_CHECK_SCRIPT = $(RIOTCPU)/$(CPU)/dist/check-fcfield-elf.sh
 

boards/common/frdm/dist/old-openocd-kx.cfg

@@ -36,7 +36,7 @@ $_TARGETNAME configure -work-area-phys 0x20000000 -work-area-size 0x1000 -work-a
 flash bank $_CHIPNAME.flash kinetis 0 0 0 0 $_TARGETNAME
 
 cortex_m reset_config sysresetreq
-#reset_config srst_only srst_nogate connect_assert_srst
+reset_config srst_only srst_nogate connect_assert_srst
 
 adapter_khz 1000
 

boards/common/frdm/dist/openocd-klx.cfg

@@ -16,7 +16,7 @@ transport select swd
 # Kinetis L series CPUs
 source [find target/klx.cfg]
 
-reset_config srst_only
+reset_config srst_only srst_nogate connect_assert_srst
 
 $_TARGETNAME configure -event gdb-attach {
   halt

boards/common/frdm/dist/openocd-kx.cfg

@@ -13,7 +13,7 @@
 # Kinetis K series CPUs
 source [find target/kx.cfg]
 
-reset_config srst_only
+reset_config srst_only srst_nogate connect_assert_srst
 
 $_TARGETNAME configure -event gdb-attach {
   halt