[ECOS] hal_delay_us() patch to at91_misc + multithreading

[Øyvind Harboe]

> I would like to see the macro
> definition upgraded to make it compulsory rather than optional, and
> require the macro to be thread-safe. 

Makes sense. I2C seems to be based upon these assumptions. 

> I am happy to do a synthetic
> target implementation, but that still leaves other architectures where
> the macro would need to be added or fixed.

How about calibrating a CPU counter loop implementaiton upon startup
using the default hardware timer in the HAL?

- a couple of ms to the startup time is a small price to pay for
  a default implementation of a HAL_DELAY_US()
- The HAL_DELAY_US() definition should state that the the accuracy
  is not very good, but that it is guaranteed to wait at least
  n us.


Is there a fundamental reason why HAL_DELAY_US() needs to be very
accurate(i.e. say <20-30%)

> 
> Bart
> 


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