cortex m3: add cortex_m3 reset_config cmd

This new cmd adds the ability to choose the Cortex-M3
reset method used.
It defaults to using SRST for reset if available otherwise
it falls back to using NVIC VECTRESET. This is known to work
on all cores.

Move any luminary specific reset handling to the stellaris cfg file.

Signed-off-by: Spencer Oliver <ntfreak@users.sourceforge.net>

tcl/target/stellaris.cfg

@@ -21,18 +21,15 @@ if { [info exists CPUTAPID ] } {
 if { [info exists WORKAREASIZE ] } {
    set _WORKAREASIZE $WORKAREASIZE
 } else {
+   # default to 8K working area
    set _WORKAREASIZE 0x2000
 }
 
 jtag newtap $_CHIPNAME cpu -irlen 4 -irmask 0xf \
 	-expected-id $_CPUTAPID -ignore-version
 
-# The "lm3s" variant uses a software reset rather than SRST.
-# This stops the debug registers from being cleared; it works
-# around an erratum which should be fixed in later silicon.
 set _TARGETNAME $_CHIPNAME.cpu
-target create $_TARGETNAME cortex_m3 -chain-position $_CHIPNAME.cpu \
-	-variant lm3s
+target create $_TARGETNAME cortex_m3 -chain-position $_CHIPNAME.cpu
 
 # 8K working area at base of ram, not backed up
 #
@@ -48,7 +45,41 @@ $_TARGETNAME configure -work-area-phys 0x20000000 -work-area-size $_WORKAREASIZE
 # configures and enables the PLL.  Or you might need to decrease
 # this, if you're using a slower clock.
 adapter_khz 500
-$_TARGETNAME configure -event reset-start {adapter_khz 500}
+
+# mrw: "memory read word", returns value of $reg
+proc mrw {reg} {
+	set value ""
+	mem2array value 32 $reg 1
+	return $value(0)
+}
+
+$_TARGETNAME configure -event reset-start {
+	adapter_khz 500
+
+	#	
+	# When nRST is asserted on most Stellaris devices, it clears some of
+	# the debug state.  The ARMv7M and Cortex-M3 TRMs say that's wrong;
+	# and OpenOCD depends on those TRMs.  So we won't use SRST on those
+	# chips.  (Only power-on reset should affect debug state, beyond a
+	# few specified bits; not the chip's nRST input, wired to SRST.)
+	#
+	# REVISIT current errata specs don't seem to cover this issue.
+	# Do we have more details than this email?
+	#   https://lists.berlios.de/pipermail
+	#	/openocd-development/2008-August/003065.html
+	#
+
+	set device_class [expr (([mrw 0x400fe000] >> 16) & 0xff)]
+	if {$device_class == 0 || $device_class == 1 || $device_class == 3} {
+		# Sandstorm, Fury and DustDevil are able to use NVIC SYSRESETREQ
+		cortex_m3 reset_config systesetreq
+	} else {
+		# Tempest and newer default to using NVIC VECTRESET
+		# this does mean a reset-init event handler is required to reset
+		# any peripherals
+		cortex_m3 reset_config vectreset
+	}
+}
 
 # flash configuration ... autodetects sizes, autoprobed
 flash bank $_CHIPNAME.flash stellaris 0 0 0 0 $_TARGETNAME