ADS1256 - too fast for Linux ?

ADS1256 - too fast for Linux ?

[Flávio Alberto Lopes Soares]

Hello all,
I need to communicate with a Texas Instruments ADS1256 SPI 24 bits ADC (
http://focus.ti.com/docs/prod/folders/print/ads1256.html) from a 2.6.32
kernel Linux running on a ARM Samsung S3C2440 microcontroller using spidev
module, to do this I need to pass a command on MOSI channel and after read
the result on MISO, but I can't read the correct data from this ADC, the
data is always corrupted, I believe (but I can't prove this) this occurs
because the very short time between the command and response, according with
the component datasheet this time is 50x the clock period, for my circuit
this is approximately 8us and I believe that there's no time to Linux get
the interrupt from SPI process this and read the SPI data, my suspicion can
be correct ? The DMA cannot solve this problem and if true how to know if it
is activated ? Only Real Time Linux can solve this ?

Thanks for all help

Flavio Alberto Lopes Soares
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Re: ADS1256 - too fast for Linux ?

[Kenneth Heitke]

On 01/14/2011 05:02 AM, Flávio Alberto Lopes Soares wrote:
> Hello all,
> I need to communicate with a Texas Instruments ADS1256 SPI 24 bits ADC (
> http://focus.ti.com/docs/prod/folders/print/ads1256.html) from a 2.6.32
> kernel Linux running on a ARM Samsung S3C2440 microcontroller using spidev
> module, to do this I need to pass a command on MOSI channel and after read
> the result on MISO, but I can't read the correct data from this ADC, the
> data is always corrupted, I believe (but I can't prove this) this occurs
> because the very short time between the command and response, according with
> the component datasheet this time is 50x the clock period, for my circuit
> this is approximately 8us and I believe that there's no time to Linux get
> the interrupt from SPI process this and read the SPI data, my suspicion can
> be correct ? The DMA cannot solve this problem and if true how to know if it
> is activated ? Only Real Time Linux can solve this ?
>
> Thanks for all help
>
> Flavio Alberto Lopes Soares
> ------------------------------------------------------------------------------
> Protect Your Site and Customers from Malware Attacks
> Learn about various malware tactics and how to avoid them. Understand
> malware threats, the impact they can have on your business, and how you
> can protect your company and customers by using code signing.
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> _______________________________________________
> spi-devel-general mailing list
> spi-devel-general-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
> https://lists.sourceforge.net/lists/listinfo/spi-devel-general
>

Curious if the SPI mode (clock polarity and phase) are set correctly for 
the device that you are communicating with.

Ken

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

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Re: ADS1256 - too fast for Linux ?

[Flávio Alberto Lopes Soares]

According with the chip datasheet the SPI must be set to mode 1 (clock start
in 0 and SPI data sample on leading edge) but it doesn't works for any spi
mode that I set, because this behavior I thought on short time to O.S. deal
with the interrupt.

How to know if DMA is activated ? DMA can solve this problem (if turned on
realy this is not the solution...)

Thanks for all help

Flavio Alberto

2011/1/14 Kenneth Heitke <kheitke-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>

> On 01/14/2011 05:02 AM, Flávio Alberto Lopes Soares wrote:
>
>> Hello all,
>> I need to communicate with a Texas Instruments ADS1256 SPI 24 bits ADC (
>> http://focus.ti.com/docs/prod/folders/print/ads1256.html) from a 2.6.32
>> kernel Linux running on a ARM Samsung S3C2440 microcontroller using spidev
>> module, to do this I need to pass a command on MOSI channel and after read
>> the result on MISO, but I can't read the correct data from this ADC, the
>> data is always corrupted, I believe (but I can't prove this) this occurs
>> because the very short time between the command and response, according
>> with
>> the component datasheet this time is 50x the clock period, for my circuit
>> this is approximately 8us and I believe that there's no time to Linux get
>> the interrupt from SPI process this and read the SPI data, my suspicion
>> can
>> be correct ? The DMA cannot solve this problem and if true how to know if
>> it
>> is activated ? Only Real Time Linux can solve this ?
>>
>> Thanks for all help
>>
>> Flavio Alberto Lopes Soares
>>
>> ------------------------------------------------------------------------------
>> Protect Your Site and Customers from Malware Attacks
>> Learn about various malware tactics and how to avoid them. Understand
>> malware threats, the impact they can have on your business, and how you
>> can protect your company and customers by using code signing.
>> http://p.sf.net/sfu/oracle-sfdevnl
>> _______________________________________________
>> spi-devel-general mailing list
>> spi-devel-general-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
>> https://lists.sourceforge.net/lists/listinfo/spi-devel-general
>>
>>
> Curious if the SPI mode (clock polarity and phase) are set correctly for
> the device that you are communicating with.
>
> Ken
>
> --
> Sent by an employee of the Qualcomm Innovation Center, Inc.
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
>
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