JTAG: fix autoprobe failure.

Fix bug noted by Øyvind: terminate the IR length autoscan when
the IR is too long, or otherwise broken.

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

1 files changed, 10 insertions, 2 deletions

diff --git a/src/jtag/core.c b/src/jtag/core.c
index da745d09..211b9d5a 100644
--- a/src/jtag/core.c
+++ b/src/jtag/core.c
@@ -1224,7 +1224,14 @@ static int jtag_validate_ircapture(void)
 		/* If we're autoprobing, guess IR lengths.  They must be at
 		 * least two bits.  Guessing will fail if (a) any TAP does
 		 * not conform to the JTAG spec; or (b) when the upper bits
-		 * captured from some conforming TAP are nonzero.
+		 * captured from some conforming TAP are nonzero.  Or if
+		 * (c) an IR length is longer than 32 bits -- which is only
+		 * an implementation limit, which could someday be raised.
+		 *
+		 * REVISIT optimization:  if there's a *single* TAP we can
+		 * lift restrictions (a) and (b) by scanning a recognizable
+		 * pattern before the all-ones BYPASS.  Check for where the
+		 * pattern starts in the result, instead of an 0...01 value.
 		 *
 		 * REVISIT alternative approach: escape to some tcl code
 		 * which could provide more knowledge, based on IDCODE; and
@@ -1233,7 +1240,8 @@ static int jtag_validate_ircapture(void)
 		if (tap->ir_length == 0) {
 			tap->ir_length = 2;
 			while ((val = buf_get_u32(ir_test, chain_pos,
-						tap->ir_length + 1)) == 1) {
+						tap->ir_length + 1)) == 1
+					&& tap->ir_length <= 32) {
 				tap->ir_length++;
 			}
 			LOG_WARNING("AUTO %s - use \"... -irlen %d\"",