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card10
openocd
Commits
fb06f353
Commit
fb06f353
authored
Jan 08, 2009
by
ntfreak
Browse files
- a few more docs tweaks
git-svn-id:
svn://svn.berlios.de/openocd/trunk@1306
b42882b7-edfa-0310-969c-e2dbd0fdcd60
parent
8e88e8f3
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1
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doc/openocd.texi
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fb06f353
...
...
@@ -3184,24 +3184,29 @@ halt
@*
In digital circuit design it is often refered to as ``clock
syncroni
z
ation'' the JTAG interface uses one clock (TCK or TCLK)
sync
h
roni
s
ation'' the JTAG interface uses one clock (TCK or TCLK)
operating at some speed, your target is operating at another. The two
clocks are not syncroni
z
ed, they are ``asynchronous''
clocks are not sync
h
roni
s
ed, they are ``asynchronous''
In order for the two to work together they must syncroni
ze
. Otherwise
In order for the two to work together they must
be
sync
h
roni
sed
. Otherwise
the two systems will get out of sync with each other and nothing will
work. There are 2 basic options. @b
{
1.
}
use a special circuit or
@b
{
2.
}
one clock must be some multile slower the the other.
work. There are 2 basic options.
@enumerate
@item
Use a special circuit.
@item
One clock must be some multiple slower the the other.
@end enumerate
@b
{
Does this really matter?
}
For some chips and some situations, this
is a non-issue (ie: A 500
mh
z ARM926) but for others - for example some
ATMEL SAM7 and SAM9 chips start operation from reset at 32k
h
z -
is a non-issue (ie: A 500
MH
z ARM926) but for others - for example some
ATMEL SAM7 and SAM9 chips start operation from reset at 32k
H
z -
program/enable the oscillators and eventually the main clock. It is in
those critical times you must slow the jtag clock to sometimes 1 to
4k
h
z.
4k
H
z.
Imagine debugging that 500
mhz arm
926 hand held battery powered device
that ``deep sleeps'' at 32k
h
z between every keystroke. It can be
Imagine debugging that 500
MHz ARM
926 hand held battery powered device
that ``deep sleeps'' at 32k
H
z between every keystroke. It can be
painful.
@b
{
Solution #1 - A special circuit
}
...
...
@@ -3213,14 +3218,14 @@ The RTCK signal often found in some ARM chips is used to help with
this problem. ARM has a good description of the problem described at
this link: @url
{
http://www.arm.com/support/faqdev/4170.html
}
[checked
28/nov/2008]. Link title: ``How does the jtag synchronisation logic
work? / how does adaptive clocking work
ing
?''.
work? / how does adaptive clocking work?''.
The nice thing about adaptive clocking is that ``battery powered hand
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.
@b
{
Solution #2 - Always works - but
is
slower
}
@b
{
Solution #2 - Always works - but
may be
slower
}
Often this is a perfectly acceptable solution.
...
...
@@ -3230,7 +3235,7 @@ depending upon the chips on your board. @b{ARM Rule of thumb} Most ARM
based systems require an 8:1 division. @b
{
Xilinx Rule of thumb
}
is
1/12 the clock speed.
Note: Many FTDI2232C based JTAG dongles are limited to 6
mh
z.
Note: Many FTDI2232C based JTAG dongles are limited to 6
MH
z.
You can still debug the 'lower power' situations - you just need to
manually adjust the clock speed at every step. While painful and
...
...
@@ -3244,7 +3249,7 @@ this way.
To set the JTAG frequency use the command:
@example
# Example: 1.234
mh
z
# Example: 1.234
MH
z
jtag
_
khz 1234
@end example
...
...
@@ -3390,7 +3395,7 @@ You can use the ``scan_chain'' command to verify and display the tap order.
Many newer devices have multiple JTAG taps. For example: ST
Microsystems STM32 chips have two taps, a ``boundary scan tap'' and
``
c
ortexM3'' tap. Example: The STM32 reference manual, Document ID:
``
C
ortexM3'' tap. Example: The STM32 reference manual, Document ID:
RM0008, Section 26.5, Figure 259, page 651/681, the ``TDI'' pin is
connected to the Boundary Scan Tap, which then connects to the
CortexM3 Tap, which then connects to the TDO pin.
...
...
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