Cortex-M3: report lockup, and recover

ARMv7-M defines a "lockup" state that's entered in certain double
fault sequences which can't be recovered from without external help.
OpenOCD has previously ignored this.

Issue a diagnostic saying the chip has locked up, and force exit
from this state by halting the core.  It's not clear this is the
best way to handle lockup; but there should now be less confusion.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>

diff --git a/src/target/cortex_m3.c b/src/target/cortex_m3.c
index adce4d9c0591826cc1ec3809b5a83c9b2c396c30..3bbe42c911c3c0baf201b44c77e15085b5e0ba0f 100644 (file)
--- a/src/target/cortex_m3.c
+++ b/src/target/cortex_m3.c
@@ -416,6 +416,21 @@ static int cortex_m3_poll(struct target *target)
                return retval;
        }
 
+       /* Recover from lockup.  See ARMv7-M architecture spec,
+        * section B1.5.15 "Unrecoverable exception cases".
+        *
+        * REVISIT Is there a better way to report and handle this?
+        */
+       if (cortex_m3->dcb_dhcsr & S_LOCKUP) {
+               LOG_WARNING("%s -- clearing lockup after double fault",
+                               target_name(target));
+               cortex_m3_write_debug_halt_mask(target, C_HALT, 0);
+               target->debug_reason = DBG_REASON_DBGRQ;
+
+               /* refresh status bits */
+               mem_ap_read_atomic_u32(swjdp, DCB_DHCSR, &cortex_m3->dcb_dhcsr);
+       }
+
        if (cortex_m3->dcb_dhcsr & S_RESET_ST)
        {
                /* check if still in reset */