Re: [Openocd-development] Getting rid of default jtag clock rate

[Karl K. <kku...@gm...>]

On Mon, Dec 6, 2010 at 12:33 PM, Øyvind Harboe <oyv...@zy...> wrote:
> I believe that there might exist a safe default or autodetection
> scheme for a specific family of parts.
>
> Such parts could use a common configuration file which
> did the autodetect/set the robust default frequency.
>
> The responsibility for deciding how to deal with JTAG clk
> is still firmly in the board configuration file though. The
> board config file might ultimately decide directly or
> indirectly to use a family-default or autodetect scheme,
> that was a decision made by the board config file.
>
> --
> Øyvind Harboe
>
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>
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All device vendors should provide BSDL files for their devices which
specify the maximum TCK speed the device can support.  This can be
used to create an auto-configuration that is fairly easy to use and
robust.

An example of this is the Xilinx programming tools.  They do an
initial shift at a low speed to find the JTAG ID's of each device.
Once the device IDs are found a search is done against the BSDL files
to find a matching description.  Once that is complete the lowest
maximum JTAG speed is used as an initial configuration based on the
BSDL information.  As an added benefit the JTAG instruction lengths
are also defined in the BSDL so it does not need to be configured
manually.

If you see failures then you have the option of manually lowering the
maximum JTAG frequency which overrides the BSDL files.

-Karl