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Cortex-M3: improved core exception handling

This updates three aspects of debugger/exception interactions:

 - Save the user's "vector_catch" setting, and restore it after reset.
   Previously, it was obliterated (rather annoyingly) each time.

 - Don't catch BusFault and HardFault exceptions unless the user says
   to do so.  Target firmware may need to handle them.

 - Don't modify SHCSR to prevent escalating BusFault to HardFault.
   Target firmware may expect to handle it as a HardFault.

Those simplifications fix several bugs.  In one annoying case, OpenOCD
would cause the target to lock up on ome faults which triggered after
the debugger disconnected.

NOTE:  a known remaining issue is that OpenOCD can still leave DEMCR
set after an otherwise-clean OpenOCD shutdown.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
tags/v0.4.0-rc2
David Brownell 12 years ago
parent
commit
d91941d5a0
3 changed files with 33 additions and 23 deletions
  1. +2
    -0
      NEWS
  2. +7
    -2
      src/target/armv7m.h
  3. +24
    -21
      src/target/cortex_m3.c

+ 2
- 0
NEWS View File

@@ -34,6 +34,8 @@ Target Layer:
- watchpoint support
Cortex-M3
- Exposed DWT registers like cycle counter
- vector_catch settings not clobbered by resets
- no longer interferes with firmware's fault handling
ETM, ETB
- "trigger_percent" command moved ETM --> ETB
- "etm trigger_debug" command added


+ 7
- 2
src/target/armv7m.h View File

@@ -106,9 +106,14 @@ struct armv7m_common
int exception_number;
struct swjdp_common swjdp_info;

uint32_t demcr;

/* Direct processor core register read and writes */
int (*load_core_reg_u32)(struct target *target, enum armv7m_regtype type, uint32_t num, uint32_t *value);
int (*store_core_reg_u32)(struct target *target, enum armv7m_regtype type, uint32_t num, uint32_t value);
int (*load_core_reg_u32)(struct target *target,
enum armv7m_regtype type, uint32_t num, uint32_t *value);
int (*store_core_reg_u32)(struct target *target,
enum armv7m_regtype type, uint32_t num, uint32_t value);

/* register cache to processor synchronization */
int (*read_core_reg)(struct target *target, unsigned num);
int (*write_core_reg)(struct target *target, unsigned num);


+ 24
- 21
src/target/cortex_m3.c View File

@@ -185,11 +185,12 @@ static int cortex_m3_endreset_event(struct target *target)
int i;
uint32_t dcb_demcr;
struct cortex_m3_common *cortex_m3 = target_to_cm3(target);
struct armv7m_common *armv7m = &cortex_m3->armv7m;
struct swjdp_common *swjdp = &cortex_m3->armv7m.swjdp_info;
struct cortex_m3_fp_comparator *fp_list = cortex_m3->fp_comparator_list;
struct cortex_m3_dwt_comparator *dwt_list = cortex_m3->dwt_comparator_list;

/* FIXME handling of DEMCR clobbers vector_catch config ... */
/* REVISIT The four debug monitor bits are currently ignored... */
mem_ap_read_atomic_u32(swjdp, DCB_DEMCR, &dcb_demcr);
LOG_DEBUG("DCB_DEMCR = 0x%8.8" PRIx32 "",dcb_demcr);

@@ -204,21 +205,14 @@ static int cortex_m3_endreset_event(struct target *target)
/* clear any interrupt masking */
cortex_m3_write_debug_halt_mask(target, 0, C_MASKINTS);

/* Enable trace and DWT; trap hard and bus faults.
/* Enable features controlled by ITM and DWT blocks, and catch only
* the vectors we were told to pay attention to.
*
* REVISIT why trap those two? And why trash the vector_catch
* config, instead of preserving it? Catching HARDERR and BUSERR
* will interfere with code that handles those itself...
* Target firmware is responsible for all fault handling policy
* choices *EXCEPT* explicitly scripted overrides like "vector_catch"
* or manual updates to the NVIC SHCSR and CCR registers.
*/
mem_ap_write_u32(swjdp, DCB_DEMCR, TRCENA | VC_HARDERR | VC_BUSERR);

/* Monitor bus faults as such (instead of as generic HARDERR), but
* leave memory management and usage faults disabled.
*
* REVISIT setting BUSFAULTENA interferes with code which relies
* on the default setting. Why do it?
*/
mem_ap_write_u32(swjdp, NVIC_SHCSR, SHCSR_BUSFAULTENA);
mem_ap_write_u32(swjdp, DCB_DEMCR, TRCENA | armv7m->demcr);

/* Paranoia: evidently some (early?) chips don't preserve all the
* debug state (including FBP, DWT, etc) across reset...
@@ -533,7 +527,7 @@ static int cortex_m3_soft_reset_halt(struct target *target)
uint32_t dcb_dhcsr = 0;
int retval, timeout = 0;

/* Enter debug state on reset; see end_reset_event() */
/* Enter debug state on reset; restore DEMCR in endreset_event() */
mem_ap_write_u32(swjdp, DCB_DEMCR,
TRCENA | VC_HARDERR | VC_BUSERR | VC_CORERESET);

@@ -782,14 +776,15 @@ static int cortex_m3_assert_reset(struct target *target)

/* clear C_HALT in dhcsr reg */
cortex_m3_write_debug_halt_mask(target, 0, C_HALT);

/* Enter debug state on reset, cf. end_reset_event() */
mem_ap_write_u32(swjdp, DCB_DEMCR,
TRCENA | VC_HARDERR | VC_BUSERR);
}
else
{
/* Enter debug state on reset, cf. end_reset_event() */
/* Halt in debug on reset; endreset_event() restores DEMCR.
*
* REVISIT catching BUSERR presumably helps to defend against
* bad vector table entries. Should this include MMERR or
* other flags too?
*/
mem_ap_write_atomic_u32(swjdp, DCB_DEMCR,
TRCENA | VC_HARDERR | VC_BUSERR | VC_CORERESET);
}
@@ -1938,12 +1933,20 @@ COMMAND_HANDLER(handle_cortex_m3_vector_catch_command)
}
}
write:
/* For now, armv7m->demcr only stores vector catch flags. */
armv7m->demcr = catch;

demcr &= ~0xffff;
demcr |= catch;

/* write, but don't assume it stuck */
/* write, but don't assume it stuck (why not??) */
mem_ap_write_u32(swjdp, DCB_DEMCR, demcr);
mem_ap_read_atomic_u32(swjdp, DCB_DEMCR, &demcr);

/* FIXME be sure to clear DEMCR on clean server shutdown.
* Otherwise the vector catch hardware could fire when there's
* no debugger hooked up, causing much confusion...
*/
}

for (unsigned i = 0; i < ARRAY_SIZE(vec_ids); i++)


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