This is a SocketCAN driver for MCP2515 with a new SPI system that
streamlines the select->write->read->deselect process and so exposes the
need to guarantee hold time between read and deselect and disable time
between deselect and next select
Looking at David's code, it seems the loop is the right answer. The DWT
cannot be used for a portable solution but maybe an inline function. Thanks
for the idea
I believe NOPs are optimized away but it seems asm("") or something close
to that is not
It would be nice to incorporate a general solution for this problem to the
Nuttx toolbox
El mié, 24 mar 2021 a las 11:24, David Sidrane (<david.sidr...@nscdg.com>)
escribió:
> What HW is this on?
>
> -----Original Message-----
> From: Grr [mailto:gebbe...@gmail.com]
> Sent: Wednesday, March 24, 2021 10:09 AM
> To: dev@nuttx.apache.org
> Subject: Re: Sleep Resolution
>
> Thank you very much for your response
>
> What I'm trying to do is to generate hold and disable times for SPI CS,
> which should be about 50 ns
>
> I started by an empty for loop but it seems optimization gets rid of it (I
> haven't researched the issue properly). Then I thought a proper function
> would be better but got stuck in that expression "sleep resolution"
>
> For that scale (10 SYSCLK cycles), a loop is probably OK but I wanted to
> make sure there's not a more appropriate system tool
>
> El mié, 24 mar 2021 a las 10:46, Sara da Cunha Monteiro de Souza (<
> saramonteirosouz...@gmail.com>) escribió:
>
> > Hi Grr,
> >
> > I have never needed to use this function neither this range (ns).
> > But I used the usleep function which resolution is defined as
> > CONFIG_USEC_PER_TICK.
> > But maybe, in your case, for such range, you should consider using a
> > hardware timer or a Timer Hook.
> > Take a look at this wiki:
> > https://cwiki.apache.org/confluence/display/NUTTX/Short+Time+Delays
> >
> > Sara
> >
> > Em qua., 24 de mar. de 2021 às 13:37, Grr <gebbe...@gmail.com> escreveu:
> >
> > > Hello to all.
> > >
> > > Looking for the right way to create a _very_ short delay (10-100 ns), I
> > > found clock_nanosleep, whose description says:
> > >
> > > "The suspension time caused by this function may be longer than
> > > requested
> > > because the argument value is rounded up to an integer multiple of the
> > > sleep resolution"
> > >
> > > What is the sleep resolution and where/how is defined?
> > >
> > > TIA
> > > Grr
> > >
> >
>
