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

[Laurent G. <lau...@am...>]

>
> 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
>   
BSDL give some informations as max JTAG frequency. The bad things are :
- not all devices come with BSDL (in general the device not supporting 
the boundary scan, do not provide BSDL files -> low cost LPC parts ...)
- Amontec has found that the frequency notified in the BSDL file is not 
really the maximum frequency but sometimes absolute max frequency - 50%!

The BSDL are not really a good thing for the major work of openocd user 
doing on-chip debug -> and not on-board debug (boundary scan)

Regards,
Laurent