Stop ignoring most scan chain validation errors

Among other things this causes startup errors to kick in the
fallback "reset harder" logic during server startup.  Comments
are also updated a bit, explaining what the various error paths
signify (in at least my observation).

There's one class of validation error that we can still plausibly
ignore:  when wrong IDCODE values are observed.

This change seems to have helped make an OMAP5912 behave much
more reliably.  There's still some post-reset flakiness, but
it's unrelated to scan verification.

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

diff --git a/src/jtag/core.c b/src/jtag/core.c
index f7d55b79301624e889e909d41537593c6b5e66d2..b8235eb1e969358f4992368a4e7fd2cbc5df9e98 100644 (file)
--- a/src/jtag/core.c
+++ b/src/jtag/core.c
@@ -892,7 +892,15 @@ static bool jtag_examine_chain_check(uint8_t *idcodes, unsigned count)
        }
 
        /* if there wasn't a single non-zero bit or if all bits were one,
-        * the scan is not valid */
+        * the scan is not valid.  We wrote a mix of both values; either
+        *
+        *  - There's a hardware issue (almost certainly):
+        *     + all-zeroes can mean a target stuck in JTAG reset
+        *     + all-ones tends to mean no target
+        *  - The scan chain is WAY longer than we can handle, *AND* either
+        *     + there are several hundreds of TAPs in bypass, or
+        *     + at least a few dozen TAPs all have an all-ones IDCODE
+        */
        if (zero_check == 0x00 || one_check == 0xff)
        {
                LOG_ERROR("JTAG scan chain interrogation failed: all %s",
@@ -988,11 +996,14 @@ static int jtag_examine_chain(void)
 {
        uint8_t idcode_buffer[JTAG_MAX_CHAIN_SIZE * 4];
        unsigned bit_count;
+       int retval;
 
        /* DR scan to collect BYPASS or IDCODE register contents.
         * Then make sure the scan data has both ones and zeroes.
         */
-       jtag_examine_chain_execute(idcode_buffer, JTAG_MAX_CHAIN_SIZE);
+       retval = jtag_examine_chain_execute(idcode_buffer, JTAG_MAX_CHAIN_SIZE);
+       if (retval != ERROR_OK)
+               return retval;
        if (!jtag_examine_chain_check(idcode_buffer, JTAG_MAX_CHAIN_SIZE))
                return ERROR_JTAG_INIT_FAILED;
 
@@ -1012,7 +1023,7 @@ static int jtag_examine_chain(void)
 
                if ((idcode & 1) == 0)
                {
-                       /* LSB must not be 0, this indicates a device in bypass */
+                       /* Zero for LSB indicates a device in bypass */
                        LOG_WARNING("TAP %s does not have IDCODE",
                                        tap->dotted_name);
                        idcode = 0;
@@ -1024,7 +1035,8 @@ static int jtag_examine_chain(void)
                {
                        /* Friendly devices support IDCODE */
                        tap->hasidcode = true;
-                       jtag_examine_chain_display(LOG_LVL_INFO, "tap/device found",
+                       jtag_examine_chain_display(LOG_LVL_INFO,
+                                       "tap/device found",
                                        tap->dotted_name, idcode);
 
                        bit_count += 32;
@@ -1033,7 +1045,7 @@ static int jtag_examine_chain(void)
 
                /* ensure the TAP ID matches what was expected */
                if (!jtag_examine_chain_match_tap(tap))
-                       return ERROR_JTAG_INIT_FAILED;
+                       retval = ERROR_JTAG_INIT_SOFT_FAIL;
        }
 
        /* Fail if too many TAPs were enabled for us to verify them all. */
@@ -1049,11 +1061,14 @@ static int jtag_examine_chain(void)
        if (jtag_examine_chain_end(idcode_buffer, bit_count,
                        8 * sizeof(idcode_buffer))) {
                LOG_ERROR("double-check your JTAG setup (interface, "
-                               "speed, TAPs, ...)");
+                               "speed, missing TAPs, ...)");
                return ERROR_JTAG_INIT_FAILED;
        }
 
-       return ERROR_OK;
+       /* Return success or, for backwards compatibility if only
+        * some IDCODE values mismatched, a soft/continuable fault.
+        */
+       return retval;
 }
 
 /*
@@ -1255,18 +1270,37 @@ int jtag_init_inner(struct command_context_s *cmd_ctx)
        if ((retval = jtag_execute_queue()) != ERROR_OK)
                return retval;
 
-       /* examine chain first, as this could discover the real chain layout */
-       if (jtag_examine_chain() != ERROR_OK)
-       {
+       /* Examine DR values first.  This discovers problems which will
+        * prevent communication ... hardware issues like TDO stuck, or
+        * configuring the wrong number of (enabled) TAPs.
+        */
+       retval = jtag_examine_chain();
+       switch (retval) {
+       case ERROR_OK:
+               /* complete success */
+               break;
+       case ERROR_JTAG_INIT_SOFT_FAIL:
+               /* For backward compatibility reasons, try coping with
+                * configuration errors involving only ID mismatches.
+                * We might be able to talk to the devices.
+                */
                LOG_ERROR("Trying to use configured scan chain anyway...");
                issue_setup = false;
+               break;
+       default:
+               /* some hard error; already issued diagnostics */
+               return retval;
        }
 
-       if (jtag_validate_ircapture() != ERROR_OK)
-       {
-               LOG_WARNING("Errors during IR capture, continuing anyway...");
-               issue_setup = false;
-       }
+       /* Now look at IR values.  Problems here will prevent real
+        * communication.  They mostly mean that the IR length is
+        * wrong ... or that the IR capture value is wrong.  (The
+        * latter is uncommon, but easily worked around:  provide
+        * ircapture/irmask values during TAP setup.)
+        */
+       retval = jtag_validate_ircapture();
+       if (retval != ERROR_OK)
+               return retval;
 
        if (issue_setup)
                jtag_notify_event(JTAG_TAP_EVENT_SETUP);

diff --git a/src/jtag/jtag.h b/src/jtag/jtag.h
index 35635cd88553bc258548e8d5f2871429be1c6d35..0126b3310294d1d0c1280af1f8e122828e5da94a 100644 (file)
--- a/src/jtag/jtag.h
+++ b/src/jtag/jtag.h
@@ -689,6 +689,7 @@ extern void jtag_sleep(uint32_t us);
 #define ERROR_JTAG_DEVICE_ERROR      (-107)
 #define ERROR_JTAG_STATE_INVALID     (-108)
 #define ERROR_JTAG_TRANSITION_INVALID (-109)
+#define ERROR_JTAG_INIT_SOFT_FAIL    (-110)
 
 /**
  * jtag_add_dr_out() is a version of jtag_add_dr_scan() which