jtag: Add an option to ignore the bypass bit

Some CPU wrongly indicate the bypas bit in the codeid.
It's the case of the NanoXplore NG-ULTRA chip that export a
configurable (and potentially invalid) ID for one of
its component.
Add an option to ignore it.

Signed-off-by: Adrien Grassein <adrien.grassein@gmail.com>
Change-Id: Ic59743f23bfc4d4e23da0e8535fec8ca9e87ff1a
Reviewed-on: https://review.openocd.org/c/openocd/+/6802
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-by: Oleksij Rempel <linux@rempel-privat.de>

doc/openocd.texi

@@ -4153,6 +4153,10 @@ option. When vendors put out multiple versions of a chip, or use the same
 JTAG-level ID for several largely-compatible chips, it may be more practical
 to ignore the version field than to update config files to handle all of
 the various chip IDs. The version field is defined as bit 28-31 of the IDCODE.
+@item @code{-ignore-bypass}
+@*Specify this to ignore the 'bypass' bit of the idcode. Some vendor put
+an invalid idcode regarding this bit. Specify this to ignore this bit and
+to not consider this tap in bypass mode.
 @item @code{-ircapture} @var{NUMBER}
 @*The bit pattern loaded by the TAP into the JTAG shift register
 on entry to the @sc{ircapture} state, such as 0x01.

src/jtag/core.c

@@ -1273,7 +1273,7 @@ static int jtag_examine_chain(void)
 			jtag_tap_init(tap);
 		}
 
-		if ((idcode & 1) == 0) {
+		if ((idcode & 1) == 0 && !tap->ignore_bypass) {
 			/* Zero for LSB indicates a device in bypass */
 			LOG_INFO("TAP %s does not have valid IDCODE (idcode=0x%" PRIx32 ")",
 					tap->dotted_name, idcode);

src/jtag/hla/hla_tcl.c

@@ -59,6 +59,7 @@ static int jim_newtap_expected_id(struct jim_nvp *n, struct jim_getopt_info *goi
 #define NTAP_OPT_DISABLED  4
 #define NTAP_OPT_EXPECTED_ID 5
 #define NTAP_OPT_VERSION   6
+#define NTAP_OPT_BYPASS    7
 
 static int jim_hl_newtap_cmd(struct jim_getopt_info *goi)
 {
@@ -75,6 +76,7 @@ static int jim_hl_newtap_cmd(struct jim_getopt_info *goi)
 		{ .name = "-disable",       .value = NTAP_OPT_DISABLED },
 		{ .name = "-expected-id",       .value = NTAP_OPT_EXPECTED_ID },
 		{ .name = "-ignore-version",       .value = NTAP_OPT_VERSION },
+		{ .name = "-ignore-bypass",       .value = NTAP_OPT_BYPASS },
 		{ .name = NULL, .value = -1},
 	};
 

src/jtag/jtag.h

@@ -135,6 +135,9 @@ struct jtag_tap {
 	/** Flag saying whether to ignore version field in expected_ids[] */
 	bool ignore_version;
 
+	/** Flag saying whether to ignore the bypass bit in the code */
+	bool ignore_bypass;
+
 	/** current instruction */
 	uint8_t *cur_instr;
 	/** Bypass register selected */

src/jtag/tcl.c

@@ -470,6 +470,7 @@ static int jim_newtap_expected_id(struct jim_nvp *n, struct jim_getopt_info *goi
 #define NTAP_OPT_DISABLED  4
 #define NTAP_OPT_EXPECTED_ID 5
 #define NTAP_OPT_VERSION   6
+#define NTAP_OPT_BYPASS    7
 
 static int jim_newtap_ir_param(struct jim_nvp *n, struct jim_getopt_info *goi,
 	struct jtag_tap *tap)
@@ -532,6 +533,7 @@ static int jim_newtap_cmd(struct jim_getopt_info *goi)
 		{ .name = "-disable",       .value = NTAP_OPT_DISABLED },
 		{ .name = "-expected-id",       .value = NTAP_OPT_EXPECTED_ID },
 		{ .name = "-ignore-version",       .value = NTAP_OPT_VERSION },
+		{ .name = "-ignore-bypass",       .value = NTAP_OPT_BYPASS },
 		{ .name = NULL,       .value = -1 },
 	};
 
@@ -617,6 +619,9 @@ static int jim_newtap_cmd(struct jim_getopt_info *goi)
 		    case NTAP_OPT_VERSION:
 			    tap->ignore_version = true;
 			    break;
+		    case NTAP_OPT_BYPASS:
+			    tap->ignore_bypass = true;
+			    break;
 		}	/* switch (n->value) */
 	}	/* while (goi->argc) */
 
@@ -887,6 +892,7 @@ static const struct command_registration jtag_subcommand_handlers[] = {
 			"['-enable'|'-disable'] "
 			"['-expected_id' number] "
 			"['-ignore-version'] "
+			"['-ignore-bypass'] "
 			"['-ircapture' number] "
 			"['-mask' number]",
 	},