flash/nor/kinetis: pull SRST low during mass erase

Mass erase operation might be impacted by different factors,
apparently the most reliable way is to do it while asserting the chip
reset line.

Change-Id: Id6ab57eaec86e402ffdf4f5c8843e7735640f03e
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/2424


Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>

src/flash/nor/kinetis.c

@@ -31,6 +31,7 @@
 #include "config.h"
 #endif
 
+#include "jtag/interface.h"
 #include "imp.h"
 #include <helper/binarybuffer.h>
 #include <target/algorithm.h>
@@ -313,6 +314,14 @@ COMMAND_HANDLER(kinetis_mdm_mass_erase)
 	 * Reset Request bit in the MDM-AP control register after
 	 * establishing communication...
 	 */
+
+	/* assert SRST */
+	if (jtag_get_reset_config() & RESET_HAS_SRST)
+		adapter_assert_reset();
+	else
+		LOG_WARNING("Attempting mass erase without hardware reset. This is not reliable; "
+			    "it's recommended you connect SRST and use ``reset_config srst_only''.");
+
 	dap_ap_select(dap, 1);
 
 	retval = kinetis_mdm_write_register(dap, MDM_REG_CTRL, MEM_CTRL_SYS_RES_REQ);
@@ -364,6 +373,9 @@ COMMAND_HANDLER(kinetis_mdm_mass_erase)
 	if (retval != ERROR_OK)
 		return retval;
 
+	if (jtag_get_reset_config() & RESET_HAS_SRST)
+		adapter_deassert_reset();
+
 	dap_ap_select(dap, original_ap);
 	return ERROR_OK;
 }