diff options
Diffstat (limited to 'doc')
| -rw-r--r-- | doc/openocd.texi | 36 |
1 files changed, 36 insertions, 0 deletions
diff --git a/doc/openocd.texi b/doc/openocd.texi index 475482df..8547fda4 100644 --- a/doc/openocd.texi +++ b/doc/openocd.texi @@ -1975,6 +1975,42 @@ When using PPDEV to access the parallel port, use the number of the parallel por you may encounter a problem. @end deffn +@deffn Command {parport_toggling_time} [nanoseconds] +Displays how many nanoseconds the hardware needs to toggle TCK; +the parport driver uses this value to obey the +@command{jtag_khz} configuration. +When the optional @var{nanoseconds} parameter is given, +that setting is changed before displaying the current value. + +The default setting should work reasonably well on commodity PC hardware. +However, you may want to calibrate for your specific hardware. +@quotation Tip +To measure the toggling time with a logic analyzer or a digital storage +oscilloscope, follow the procedure below: +@example +> parport_toggling_time 1000 +> jtag_khz 500 +@end example +This sets the maximum JTAG clock speed of the hardware, but +the actual speed probably deviates from the requested 500 kHz. +Now, measure the time between the two closest spaced TCK transitions. +You can use @command{runtest 1000} or something similar to generate a +large set of samples. +Update the setting to match your measurement: +@example +> parport_toggling_time <measured nanoseconds> +@end example +Now the clock speed will be a better match for @command{jtag_khz rate} +commands given in OpenOCD scripts and event handlers. + +You can do something similar with many digital multimeters, but note +that you'll probably need to run the clock continuously for several +seconds before it decides what clock rate to show. Adjust the +toggling time up or down until the measured clock rate is a good +match for the jtag_khz rate you specified; be conservative. +@end quotation +@end deffn + @deffn {Config Command} {parport_write_on_exit} (on|off) This will configure the parallel driver to write a known cable-specific value to the parallel interface on exiting OpenOCD |