From 6996e628f826d9a5c2c23ffe307fc3d7486aa15f Mon Sep 17 00:00:00 2001 From: oharboe Date: Sun, 12 Jul 2009 14:08:16 +0000 Subject: [PATCH] David Brownell Mention how parallel clock voting implementations of RTCK work, and reference TI's free VHDL code. git-svn-id: svn://svn.berlios.de/openocd/trunk@2508 b42882b7-edfa-0310-969c-e2dbd0fdcd60 --- doc/openocd.texi | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/doc/openocd.texi b/doc/openocd.texi index 5537ba809..3a7538ee4 100644 --- a/doc/openocd.texi +++ b/doc/openocd.texi @@ -5661,6 +5661,18 @@ held device example'' - the adaptiveness works perfectly all the time. One can set a break point or halt the system in the deep power down code, slow step out until the system speeds up. +Note that adaptive clocking may also need to work at the board level, +when a board-level scan chain has multiple chips. +Parallel clock voting schemes are good way to implement this, +both within and between chips, and can easily be implemented +with a CPLD. +It's not difficult to have logic fan a module's input TCK signal out +to each TAP in the scan chain, and then wait until each TAP's RTCK comes +back with the right polarity before changing the output RTCK signal. +Texas Instruments makes some clock voting logic available +for free (with no support) in VHDL form; see +@url{http://tiexpressdsp.com/index.php/Adaptive_Clocking} + @b{Solution #2 - Always works - but may be slower} Often this is a perfectly acceptable solution.