How to mesure current SPI transfer speed

How to mesure current SPI transfer speed

[Kevyn-Alexandre Paré]

Hi,

What's the best way to calculate the current SPI transfer speed?

Right now I use something like that and transfer one spi_message with 1
spi_transfer of 100000 bytes and I do the math... I know that this is
not accurate and was wondering if anyone have a better way?


struct timeval tv_before;
struct timeval tv_after;

do_gettimeofday(&tv_before);
    status = spi_sync(spike_dev.spi_device, &spike_ctl.msg);
do_gettimeofday(&tv_after);
    long elapsedTime = (tv_after.tv_usec - tv_before.tv_usec);


Thx

--
Kevyn-Alexandre Pare


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Re: How to mesure current SPI transfer speed

[Jassi Brar]

On Sat, Jan 8, 2011 at 3:51 AM, Kevyn-Alexandre Paré
<kapare@rogue-research.com> wrote:
> Hi,
>
> What's the best way to calculate the current SPI transfer speed?
>
> Right now I use something like that and transfer one spi_message with 1
> spi_transfer of 100000 bytes and I do the math... I know that this is
> not accurate and was wondering if anyone have a better way?
>
>
> struct timeval tv_before;
> struct timeval tv_after;
>
> do_gettimeofday(&tv_before);
>    status = spi_sync(spike_dev.spi_device, &spike_ctl.msg);
> do_gettimeofday(&tv_after);
>    long elapsedTime = (tv_after.tv_usec - tv_before.tv_usec);

Transfer speed is tightly linked to MOSI/MISO bit rates.
But the overall throughput would depend on the protocol that
you run over SPI.

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Re: How to mesure current SPI transfer speed

[Kevyn-Alexandre Paré]

On Sat, 2011-01-08 at 11:16 +0900, Jassi Brar wrote:
> On Sat, Jan 8, 2011 at 3:51 AM, Kevyn-Alexandre Paré
> <kapare@rogue-research.com> wrote:
> > Hi,
> >
> > What's the best way to calculate the current SPI transfer speed?
> >
> > Right now I use something like that and transfer one spi_message with 1
> > spi_transfer of 100000 bytes and I do the math... I know that this is
> > not accurate and was wondering if anyone have a better way?
> >
> >
> > struct timeval tv_before;
> > struct timeval tv_after;
> >
> > do_gettimeofday(&tv_before);
> >    status = spi_sync(spike_dev.spi_device, &spike_ctl.msg);
> > do_gettimeofday(&tv_after);
> >    long elapsedTime = (tv_after.tv_usec - tv_before.tv_usec);
> 
> Transfer speed is tightly linked to MOSI/MISO bit rates.
> But the overall throughput would depend on the protocol that
> you run over SPI.

Effectively, but how to monitor that I respect, for example, a
requirement of 5Mbps with a chip... I'm already sending data at

#define SPI_BUS_SPEED 5000000
spi_device->max_speed_hz = SPI_BUS_SPEED;

So does this settings ensure it to always be at 5Mhz?

I will try to test it by settings it to higher speed to see what happen
ex: 48000000 (48Mhz)

Regards,

--
Kevyn-Alexandre Pare





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Re: How to mesure current SPI transfer speed

[Jassi Brar]

On Tue, Jan 11, 2011 at 5:25 AM, Kevyn-Alexandre Paré
<kapare@rogue-research.com> wrote:
>> > What's the best way to calculate the current SPI transfer speed?
>> >
>> > Right now I use something like that and transfer one spi_message with 1
>> > spi_transfer of 100000 bytes and I do the math... I know that this is
>> > not accurate and was wondering if anyone have a better way?
>> >
>> >
>> > struct timeval tv_before;
>> > struct timeval tv_after;
>> >
>> > do_gettimeofday(&tv_before);
>> >    status = spi_sync(spike_dev.spi_device, &spike_ctl.msg);
>> > do_gettimeofday(&tv_after);
>> >    long elapsedTime = (tv_after.tv_usec - tv_before.tv_usec);
>>
>> Transfer speed is tightly linked to MOSI/MISO bit rates.
>> But the overall throughput would depend on the protocol that
>> you run over SPI.
>
> Effectively, but how to monitor that I respect, for example, a
> requirement of 5Mbps with a chip... I'm already sending data at
>
> #define SPI_BUS_SPEED 5000000
> spi_device->max_speed_hz = SPI_BUS_SPEED;
>
> So does this settings ensure it to always be at 5Mhz?

Not always.
Your protocol driver can theoretically set any rate from
[0, SPI_BUS_SPEED]. And bits would be shifted in/out
at that rate whenever the protocol driver has some data to recv/send.
Usually, streaming devices(like DMB) will have more or less the same
throughput equal to the clock rate, but bulk devices (like MMC) may not.

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