JTAG: fix autoprobe failure.

[openocd.git] / src / jtag / core.c

diff --git a/src/jtag/core.c b/src/jtag/core.c
index da745d09a22535fb0c688dbf76718e230d52937c..211b9d5ad9e70ff1d41fa05a1259cc52f76d8e47 100644 (file)
--- 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\"",