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

[Michael S. <rin...@di...>]

On 12/06/2010 10:53 AM, Laurent Gauch wrote:
>
>
> Øyvind Harboe wrote:
>> I don't subscribe to the idea that there is a safe, correct and robust
>> default setting for JTAG clock, better to make the user get a
>> good error message that points him in the right direction.
>>
>> 1MHz will fail on plenty of cards (with RC oscilators typically).
>>
>>   
> I do not say the 1MHz is safe correct and robust, but having a known
> 1MHZ JTAG at startup, is is a good way to let the user do something
> with openocd without having to obligatory set a specific frequency in
> the script. If the 1MHZ failed, it failed ... and something specific
> must be present in the script.
1MHz is just as bad as as default as 30MHz. It may work in more cases,
but it is still broken in some.

IMHO, there are two possibilities:
 - we find a method to auto-configure a default that works in *every* case
 - or we require a configuration value that works (that may be chip- or
board-specific).

Having a default that works most of the time, but causes strange effects
in some cases, is really bad useability.


> THE SAFE CORRECT ROBUST frequency can never be known as static ! A
> good JTAG software has to find this frequency by itself
> (auto-detecting the max safe JTAG frequency );-)
Then how do you propose to implement such an auto-detection?

> The default frequency could be 10KHz instead 1MHZ ...
Until some new really-low-power chip comes along that starts at an even
lower internal clock - this does not sound robust.

cu
Michael