target/stm32f7x: Clear stuck HSE clock with CSS

Change-Id: Ica0025ea465910dd664ab546b66f4f25b271f1f5
Signed-off-by: Christopher Head <chead@zaber.com>
Reviewed-on: http://openocd.zylin.com/4570
Tested-by: jenkins
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>

1 files changed, 39 insertions, 0 deletions

diff --git a/tcl/target/stm32f7x.cfg b/tcl/target/stm32f7x.cfg
index 98f3eea..562de30 100755
--- a/tcl/target/stm32f7x.cfg
+++ b/tcl/target/stm32f7x.cfg
@@ -84,6 +84,45 @@ $_TARGETNAME configure -event trace-config {
 }
 
 $_TARGETNAME configure -event reset-init {
+	# If the HSE was previously enabled and the external clock source
+	# disappeared, RCC_CR.HSERDY can get stuck at 1 and the PLL cannot be
+	# properly switched back to HSI. This situation persists even over a system
+	# reset, including a pin reset via SRST. However, activating the clock
+	# security system will detect the problem and clear HSERDY to 0, which in
+	# turn allows the PLL to switch back to HSI properly. Since we just came
+	# out of reset, HSEON should be 0. If HSERDY is 1, then this situation must
+	# have happened; in that case, activate the clock security system to clear
+	# HSERDY.
+	if {[mrw 0x40023800] & 0x00020000} {
+		mmw 0x40023800 0x00090000 0 ;# RCC_CR = CSSON | HSEON
+		sleep 10                    ;# Wait for CSS to fire, if it wants to
+		mmw 0x40023800 0 0x00090000 ;# RCC_CR &= ~CSSON & ~HSEON
+		mww 0x4002380C 0x00800000   ;# RCC_CIR = CSSC
+		sleep 1                     ;# Wait for CSSF to clear
+	}
+
+	# If the clock security system fired, it will pend an NMI. A pending NMI
+	# will cause a bad time for any subsequent executing code, such as a
+	# programming algorithm.
+	if {[mrw 0xE000ED04] & 0x80000000} {
+		# ICSR.NMIPENDSET reads as 1. Need to clear it. A pending NMI can’t be
+		# cleared by any normal means (such as ICSR or NVIC). It can only be
+		# cleared by entering the NMI handler or by resetting the processor.
+		echo "[target current]: Clock security system generated NMI. Clearing."
+
+		# Keep the old DEMCR value.
+		set old [mrw 0xE000EDFC]
+
+		# Enable vector catch on reset.
+		mww 0xE000EDFC 0x01000001
+
+		# Issue local reset via AIRCR.
+		mww 0xE000ED0C 0x05FA0001
+
+		# Restore old DEMCR value.
+		mww 0xE000EDFC $old
+	}
+
 	# Configure PLL to boost clock to HSI x 10 (160 MHz)
 	mww 0x40023804 0x08002808   ;# RCC_PLLCFGR 16 Mhz /10 (M) * 128 (N) /2(P)
 	mww 0x40023C00 0x00000107   ;# FLASH_ACR = PRFTBE | 7(Latency)