SPI-ADC

SPI-ADC

[arjun rath]

Hi Everybody,

I am using a SPI based 12 bit adc(max1241) from maxim.I am trying to read
the value from adc  using spi_read() in linux kernel.But every time i used
to read i am getting *0xff* only.(i have to read two consecutive bytes).To
the adc chip i am probing with CRO which always shows DOUT pin of ADC as
high provided the input to ADC is always 1.1 volt.
And the clock is also coming as seen in the CRO with Chip select line going
low.

Is it a delay problem since for adc's we have to wait for sometime for
conversion of data....????

Can anybody give some suggestion regarding this....

Thanks in advance
------------------------------------------------------------------------------

Re: SPI-ADC

[H Hartley Sweeten]

On Wednesday, April 21, 2010 11:20 PM, arjun rath wrote:
> Hi Everybody,
> 
> I am using a SPI based 12 bit adc(max1241) from maxim.I am trying to read
> the value from adc  using spi_read() in linux kernel.But every time i used
> to read i am getting *0xff* only.(i have to read two consecutive bytes).To
> the adc chip i am probing with CRO which always shows DOUT pin of ADC as
> high provided the input to ADC is always 1.1 volt.
> And the clock is also coming as seen in the CRO with Chip select line going
> low.
> 
> Is it a delay problem since for adc's we have to wait for sometime for
> conversion of data....????
> 
> Can anybody give some suggestion regarding this....

According to the datasheet, to start a conversion with the max124[0|1] you
need to pull the chip select low.  At the falling edge the T/H enters its
Hold mode and a conversion is initiated.  During this time the ADC will keep
the DOUT pin pulled low and the SCLK must be kept low during the conversion.
The end of conversion is signaled by DOUT going high.  At this point the
data can be shifted out with the SCLK signal.

It appears the SPI API is supposed to support this with the SPI_READY mode
flag.  But, the only SPI master driver in mainline that supports this flag
is the davinci_spi driver.

Regards,
Hartley
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Re: SPI-ADC

[H Hartley Sweeten]

On Thursday, April 22, 2010 10:09 PM, arjun rath wrote:
> Hi ,

Please do a reply-all to keep the thread on the lists.  Also, please
do not top-post.  I fixed both here...

> On Thu, Apr 22, 2010 at 9:53 PM, H Hartley Sweeten <hartleys-3FF4nKcrg1dE2c76skzGb0EOCMrvLtNR@public.gmane.org> wrote:
>> On Wednesday, April 21, 2010 11:20 PM, arjun rath wrote:
>>> Hi Everybody,
>>>
>>> I am using a SPI based 12 bit adc(max1241) from maxim.I am trying to read
>>> the value from adc  using spi_read() in linux kernel.But every time i used
>>> to read i am getting *0xff* only.(i have to read two consecutive bytes).To
>>> the adc chip i am probing with CRO which always shows DOUT pin of ADC as
>>> high provided the input to ADC is always 1.1 volt.
>>> And the clock is also coming as seen in the CRO with Chip select line going
>>> low.
>>>
>>> Is it a delay problem since for adc's we have to wait for sometime for
>>> conversion of data....????
>>>
>>> Can anybody give some suggestion regarding this....
>>	
>> According to the datasheet, to start a conversion with the max124[0|1] you
>> need to pull the chip select low.  At the falling edge the T/H enters its
>> Hold mode and a conversion is initiated.  During this time the ADC will keep
>> the DOUT pin pulled low and the SCLK must be kept low during the conversion.
>> The end of conversion is signaled by DOUT going high.  At this point the
>> data can be shifted out with the SCLK signal.
>>	
>> It appears the SPI API is supposed to support this with the SPI_READY mode
>> flag.  But, the only SPI master driver in mainline that supports this flag
>> is the davinci_spi driver.
	
> Thanks for the reply.
>
> You mean to say with atmel spi master it is not possible(at91sam9263)...
> and to start the conversation i am pulling the chip select line low...

Looking at the atmel_spi driver it appears that it currently does not
support the SPI_READY mode.  So yes, with the driver as it is now it will
not work correctly with the max124[0|1] parts.

> Is it possible that i can write the serial protocol procedure what ever
> given in the datasheet instead of spi.

The max124[0|1] is still a spi device so using the atmel_spi driver is
the correct route.  You just need to add the necessary support to the
driver to handle the SPI_READY mode.

I added the author, Haavard Skinnemoen, to the Cc list to see if he has any
ideas to help.

Regards,
Hartley



------------------------------------------------------------------------------

Re: SPI-ADC

[Haavard Skinnemoen]

H Hartley Sweeten <hartleys-3FF4nKcrg1dE2c76skzGb0EOCMrvLtNR@public.gmane.org> wrote:
> The max124[0|1] is still a spi device so using the atmel_spi driver is
> the correct route.  You just need to add the necessary support to the
> driver to handle the SPI_READY mode.

If there's only one master driver which supports this flag, it sounds
to me like it would be a _lot_ easier in the long run to instead teach
the device driver to deal with drivers which don't support this mode.

The atmel_spi hardware doesn't have any hardware support for this mode
as far as I know, so the implementation will be very CPU-intensive
either way.

But the best solution is probably to replace the ADC with one that
doesn't have a completely boneheaded interface.

Haavard

------------------------------------------------------------------------------

Re: SPI-ADC

[arjun rath]

>> The max124[0|1] is still a spi device so using the atmel_spi driver is
>> the correct route.  You just need to add the necessary support to the
>> driver to handle the SPI_READY mode.
>
> If there's only one master driver which supports this flag, it sounds
> to me like it would be a _lot_ easier in the long run to instead teach
> the device driver to deal with drivers which don't support this mode.
>
> The atmel_spi hardware doesn't have any hardware support for this mode
> as far as I know, so the implementation will be very CPU-intensive
> either way.
>
> But the best solution is probably to replace the ADC with one that
> doesn't have a completely boneheaded interface.
>
> Haavard


Now i written the program with simple IO port reading/writing since
those pins can be also configured as gpio pins.And when pulling the CS
line LOW and checking the probe DOUT data is showing in the CRO but
while reading the DOUT pin it always shows 1(high) only.

Really its getting tougher and tougher

On Mon, Apr 26, 2010 at 12:56 PM, Haavard Skinnemoen
<haavard.skinnemoen-AIFe0yeh4nAAvxtiuMwx3w@public.gmane.org> wrote:
> H Hartley Sweeten <hartleys-3FF4nKcrg1dE2c76skzGb0EOCMrvLtNR@public.gmane.org> wrote:
>> The max124[0|1] is still a spi device so using the atmel_spi driver is
>> the correct route.  You just need to add the necessary support to the
>> driver to handle the SPI_READY mode.
>
> If there's only one master driver which supports this flag, it sounds
> to me like it would be a _lot_ easier in the long run to instead teach
> the device driver to deal with drivers which don't support this mode.
>
> The atmel_spi hardware doesn't have any hardware support for this mode
> as far as I know, so the implementation will be very CPU-intensive
> either way.
>
> But the best solution is probably to replace the ADC with one that
> doesn't have a completely boneheaded interface.
>
> Haavard
>

------------------------------------------------------------------------------

Re: SPI-ADC

[Ben Gamari]

Excerpts from arjun rath's message of Sun Feb 14 23:29:18 -0500 2010:
> Let us try and see .If any body is having a reference driver for SPI based
> ADC,they can share.
> 
Have a look here[1]. The code certainly isn't finished (we're at a
similar stage of development as you, it seem), but you should get the
rough idea.

Cheers,

- Ben


[1] http://goldnerlab.physics.umass.edu/git?p=tracker.git;a=blob;f=max5134.h;h=4aa93485347b5fb9f595b75147aeff3579c04966;hb=HEAD

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Re: SPI-ADC

[jassi brar]

On Mon, Feb 15, 2010 at 1:29 PM, arjun rath <rath.arjun-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> Let us try and see .If any body is having a reference driver for SPI based
> ADC,they can share.
Don't think you need to anything 'ADC specific' all u need is to _use_
your SPI driver.
grep for spi_sync in linux/drivers/ and refer to any spi user driver.

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Re: SPI-ADC

[arjun rath]

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Hi all,

Thanks for the suggestions.

Actually i am new to SPI,and all related ADC drivers in the latest kernels
are through I2C.i am going to use an temperature module through this adc
connected through SPI.so i think i am going to read the data only,no data
writing is required.

Let us try and see .If any body is having a reference driver for SPI based
ADC,they can share.

Regards

Arjun

On Sun, Feb 14, 2010 at 2:50 AM, Linus Walleij
<linus.ml.walleij-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>wrote:

> 2010/2/13 Jonathan Cameron <kernel-tko9wxEg+fIOOJlXag/Snyp2UmYkHbXO@public.gmane.org>:
>
> >>> can anybody share how to start a spi based ADC linux driver.I am having
> a
> >>> MAXIM 1242 ADC chip.
> >>
> >> The ḱernel does not contain any generic ADC subsystem abstraction
> >> (...)
> >
> > That's not entirely true.  These are covered by the IIO subsystem which
> > is admittedly currently in staging as some elements still need cleaning
> up.
> > (...)
> > ADC drivers are under drivers/staging/iio/adc.
>
> Great stuff. I knew about IIO and then it fell out of my mind, how
> could I...
>
> What strikes me especially about IIO is the underlying assumption, which I
> think ought to be written in clear somewhere where I missed it, and that
> is that all IIO drivers are supposed to deliver values and be controller
> from
> userspace with this nice ABI, and nothing's wrong with that of course.
>
> But I'm hinting about a few in-kernel uses: for AB3100 we have a battery
> charging mechanism, which use a (calibrated) ADC value supporting the
> bulk of the driver in the power/ subsystem.
>
> As it looks today IIO is not intended for the case where another subsystem
> needs to grab and use and ADC for its own purposes. Is this correct or did
> I get it all wrong?
>
> Would you say it'd be a good idea to hack the IIO ADC interface (for
> example) to be used also internally in the kernel, or would that violate
> the idea behind IIO?
>
> If these are disparate categories it would warrant a separate adc/
> subsystem, see.
>
> > Currently all discussions take place on LKML, but we are working on a
> more
> > focused alternative list which I'll announce once it is sorted out.
>
> LKML is just fine with me, for one.
>
> Yours,
> Linus Walleij
>

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Re: SPI-ADC

[Ben Gamari]

Excerpts from arjun rath's message of Sat Feb 13 00:48:40 -0500 2010:
> Hi everybody,
> 
> can anybody share how to start a spi based ADC linux driver.I am having a
> MAXIM 1242 ADC chip.
> 
> Can anybody share some reference driver for the same chip
> 
I've recently been working on a design for a data acquisition
board to interface with the Beagle Board using the Maxim 5134 and 1270.
I'm using the spidev driver to interface with the devices from
user-space. Documentation on this driver can be found in the
Documentation/spi/spidev file of the Linux kernel tree. My code can be
found at [1]. Hope things are going well,

- Ben


[1] http://goldnerlab.physics.umass.edu/git?p=tracker.git;a=tree

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SPI-ADC

[arjun rath]

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Hi everybody,

can anybody share how to start a spi based ADC linux driver.I am having a
MAXIM 1242 ADC chip.

Can anybody share some reference driver for the same chip

Thanks in advance

Arjun

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