[PATCH]: de595c7a21 target/cortex_m: supress historical reset detection

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"Tomas Vanek <va...@fb...>" just uploaded a new patch set to Gerrit, which you can find at https://review.openocd.org/c/openocd/+/7109

-- gerrit

commit de595c7a218d33776e961e1d74e763336bb0cf61
Author: Tomas Vanek <va...@fb...>
Date:   Tue Aug 2 11:44:43 2022 +0200

    target/cortex_m: supress historical reset detection
    
    The S_RESET_ST sticky bit is reset after DHCSR read.
    It is set at power-on reset and keeps active until the debuger reads DHCSR.
    
    Ignore S_RESET_ST at the very first read after OpenOCD start
    and suppress possibly misleading message "external reset detected"
    if we cannot guarantee the reset happened recently.
    
    Change-Id: I15217c2ca6f69ac97aff8be86bce67cba94a42cd
    Signed-off-by: Tomas Vanek <va...@fb...>

diff --git a/src/target/cortex_m.c b/src/target/cortex_m.c
index 9497aa0373..043b3af100 100644
--- a/src/target/cortex_m.c
+++ b/src/target/cortex_m.c
@@ -118,6 +118,7 @@ static inline void cortex_m_cumulate_dhcsr_sticky(struct cortex_m_common *cortex
 		uint32_t dhcsr)
 {
 	cortex_m->dcb_dhcsr_cumulated_sticky |= dhcsr;
+	cortex_m->dcb_dhcsr_sticky_is_recent = true;
 }
 
 /** Read DCB DHCSR register to cortex_m->dcb_dhcsr and cumulate
@@ -2396,6 +2397,18 @@ int cortex_m_examine(struct target *target)
 		retval = target_read_u32(target, DCB_DHCSR, &cortex_m->dcb_dhcsr);
 		if (retval != ERROR_OK)
 			return retval;
+
+		/*  Don't cumulate sticky S_RESET_ST at the very first read of DHCSR
+		 *  as S_RESET_ST may indicate a reset that happened long time ago
+		 *  (most probably the power-on reset before OpenOCD was started).
+		 *  As we are just initializing the debug system we do not need
+		 *  to call cortex_m_endreset_event() in the folowing poll.
+		 */
+		if (!cortex_m->dcb_dhcsr_sticky_is_recent
+			       && cortex_m->dcb_dhcsr & S_RESET_ST) {
+			LOG_TARGET_DEBUG(target, "reset happened some time ago, ignore");
+			cortex_m->dcb_dhcsr &= ~S_RESET_ST;
+		}
 		cortex_m_cumulate_dhcsr_sticky(cortex_m, cortex_m->dcb_dhcsr);
 
 		if (!(cortex_m->dcb_dhcsr & C_DEBUGEN)) {
diff --git a/src/target/cortex_m.h b/src/target/cortex_m.h
index 3f0d55c1c2..4243b50841 100644
--- a/src/target/cortex_m.h
+++ b/src/target/cortex_m.h
@@ -204,6 +204,8 @@ struct cortex_m_common {
 	/* Context information */
 	uint32_t dcb_dhcsr;
 	uint32_t dcb_dhcsr_cumulated_sticky;
+	/* DCB DHCSR has been at least once read, so the sticky bits have been reset */
+	bool dcb_dhcsr_sticky_is_recent;
 	uint32_t nvic_dfsr;  /* Debug Fault Status Register - shows reason for debug halt */
 	uint32_t nvic_icsr;  /* Interrupt Control State Register - shows active and pending IRQ */
 

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