Commit afed39c0 authored by David Brownell's avatar David Brownell
Browse files

User's Guide: TAP setup tweakage

Highlight that the "-expected-id" probably comes from vendor
documentation, and that it *should* be used where possible.

Don't use ircapture/irmask in examples, to help discourage
use of those params when they're not required.  Explain a
bit better about why/when those params get used.

Signed-off-by: default avatarDavid Brownell <>
parent 98788d7a
......@@ -1339,8 +1339,7 @@ The config file for the Atmel AT91SAM7X256
looks (in part) like this:
jtag newtap $_CHIPNAME cpu -irlen 4 -ircapture 0x1 -irmask 0xf \
-expected-id $_CPUTAPID
jtag newtap $_CHIPNAME cpu -irlen 4 -expected-id $_CPUTAPID
@end example
A board with two such at91sam7 chips would be able
......@@ -2496,7 +2495,7 @@ requires explicit configuration of all TAP devices using
A command like this would declare one tap and name it @code{chip1.cpu}:
jtag newtap chip1 cpu -irlen 7 -ircapture 0x01 -irmask 0x55
jtag newtap chip1 cpu -irlen 4 -expected-id 0x3ba00477
@end example
Each target configuration file lists the TAPs provided
......@@ -2641,13 +2640,21 @@ These codes are not required by all JTAG devices.
ID code could appear (for example, multiple versions).
Specify @var{number} as zero to suppress warnings about IDCODE
values that were found but not included in the list.
Provide this value if at all possible, since it lets OpenOCD
tell when the scan chain it sees isn't right. These values
are provided in vendors' chip documentation, usually a technical
reference manual. Sometimes you may need to probe the JTAG
hardware to find these values.
@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.
JTAG requires the two LSBs of this value to be 01.
By default, @code{-ircapture} and @code{-irmask} are set
up to verify that two-bit value; but you may provide
additional bits, if you know them.
up to verify that two-bit value. You may provide
additional bits, if you know them, or indicate that
a TAP doesn't conform to the JTAG specification.
@item @code{-irmask} @var{NUMBER}
@*A mask used with @code{-ircapture}
to verify that instruction scans work correctly.
......@@ -6149,12 +6156,13 @@ to execute before they take effect.
@end deffn
@c tms_sequence (short|long)
@c ... temporary, debug-only, probably gone before 0.2 ships
@c ... temporary, debug-only, other than USBprog bug workaround...
@deffn Command {verify_ircapture} (@option{enable}|@option{disable})
Verify values captured during @sc{ircapture} and returned
during IR scans. Default is enabled, but this can be
overridden by @command{verify_jtag}.
This flag is ignored when validating JTAG chain configuration.
@end deffn
@deffn Command {verify_jtag} (@option{enable}|@option{disable})
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