flash: add stm32lx loader Hard Fault workaround

An issue has been seen with the stm32lx flash driver that if a
power cycle/reset is applied after a erase, any ram loader will Hard Fault
on execution.

A similar issue is mentioned in the errata for the device.
Two solution's seem to workaround this issue:
1, Handle the exception, this means adding exception vectors to the loader
   and changing the exception address using nvic vtor register.
2. falling back to using slower direct page writes - approx 50% slower.

Using solution 1 would mean restrictions are placed on the loader location.
Solution 2 was chosen mainly as it was simpler too implement.

Change-Id: I429f06b5a3e3b1d8de90071a88a7df11fc9b46a7
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/1010
Tested-by: jenkins

1 files changed, 53 insertions, 0 deletions

diff --git a/src/flash/nor/stm32lx.c b/src/flash/nor/stm32lx.c
index 264a45c..fc0fb9e 100644
--- a/src/flash/nor/stm32lx.c
+++ b/src/flash/nor/stm32lx.c
@@ -32,6 +32,7 @@
 #include <helper/binarybuffer.h>
 #include <target/algorithm.h>
 #include <target/armv7m.h>
+#include <target/cortex_m.h>
 
 /* stm32lx flash register locations */
 
@@ -299,6 +300,18 @@ static int stm32lx_write_half_pages(struct flash_bank *bank, uint8_t *buffer,
 		return retval;
 	}
 
+	struct armv7m_common *armv7m = target_to_armv7m(target);
+	if (armv7m == NULL) {
+
+		/* something is very wrong if armv7m is NULL */
+		LOG_ERROR("unable to get armv7m target");
+		return retval;
+	}
+
+	/* save any DEMCR flags and configure target to catch any Hard Faults */
+	uint32_t demcr_save = armv7m->demcr;
+	armv7m->demcr = VC_HARDERR;
+
 	/* Loop while there are bytes to write */
 	while (count > 0) {
 		uint32_t this_count;
@@ -324,6 +337,10 @@ static int stm32lx_write_half_pages(struct flash_bank *bank, uint8_t *buffer,
 		if (retval != ERROR_OK)
 			break;
 
+		/* check for Hard Fault */
+		if (armv7m->exception_number == 3)
+			break;
+
 		/* 6: Wait while busy */
 		retval = stm32lx_wait_until_bsy_clear(bank);
 		if (retval != ERROR_OK)
@@ -334,6 +351,42 @@ static int stm32lx_write_half_pages(struct flash_bank *bank, uint8_t *buffer,
 		count -= this_count;
 	}
 
+	/* restore previous flags */
+	armv7m->demcr = demcr_save;
+
+	if (armv7m->exception_number == 3) {
+
+		/* the stm32l15x devices seem to have an issue when blank.
+		 * if a ram loader is executed on a blank device it will
+		 * Hard Fault, this issue does not happen for a already programmed device.
+		 * A related issue is described in the stm32l151xx errata (Doc ID 17721 Rev 6 - 2.1.3).
+		 * The workaround of handling the Hard Fault exception does work, but makes the
+		 * loader more complicated, as a compromise we manually write the pages, programming time
+		 * is reduced by 50% using this slower method.
+		 */
+
+		LOG_WARNING("couldn't use loader, falling back to page memory writes");
+
+		while (count > 0) {
+			uint32_t this_count;
+			this_count = (count > 128) ? 128 : count;
+
+			/* Write the next half pages */
+			retval = target_write_buffer(target, address, this_count, buffer);
+			if (retval != ERROR_OK)
+				break;
+
+			/* Wait while busy */
+			retval = stm32lx_wait_until_bsy_clear(bank);
+			if (retval != ERROR_OK)
+				break;
+
+			buffer += this_count;
+			address += this_count;
+			count -= this_count;
+		}
+	}
+
 	if (retval == ERROR_OK)
 		retval = stm32lx_lock_program_memory(bank);