On Fri, 11 Jun 1999, Peter Wurmsdobler wrote:
> However, I am not entirely satisfied with my architecture:
> a kernel module having registered an RTirq puts captured
> data into shared memory at a given frequency as unsigned
> short int. From user space, these values are converted
> into Volts and later on in other units. What bothers me
> is that the conversion depends on DAQ board settings. I
> would prefer a clearer interface between the DAQ board
> specific functions and the rt-module such that they
> already deliver floats representing Volts into shared
> memory.
>
You might want to reconsider this. It may be better to keep your
short (only 2 bytes, 12 or 16 bits usually) bitcounts from the DAQ board
and retain a conversion factor to covert them to proper floating point
voltages. The conversion doubles (for 4 byte floats) the storage
of the data and does not improve the information in the data (you still
have quantized voltages). You can simply spit back the conversion
factor or card parameters from the RT-Task and allow the user-space
code to calculate the floating point values as needed.
This avoids the use of the FPU in the ISR where it is not actually
needed to complete the task.
-Don
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