LINUX AT91 ADC DRIVER

April 8, 2020 By:

Once this pin will have edges from logical 1 to logical 0 or the other way around , these will be detected by the ADC. Reading this file should return you a weird looking string. To produce a kernel image suitable for U-Boot: An oscilloscope can be used to measure exact number of edges versus the exact number of samples provided by the ADC, to see the reliability. The pins for the two last channels won’t be multiplexed as ADC outputs, and the channels won’t be available in the driver. This could not be achieved if we did not use DMA, because the kernel would be interrupted for each conversion, and it would hog the CPU.

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For the G20, you have two types of hardware triggers, either timer counters are the trigger for the conversion, either an external pin is used to provide such an input. To achieve a better speed, we can increase the clock to 20 mHz, which is the maximum supported sample rate: The ADC will monitor this pin once it’s configured to do so.

UsingSAMA5D2ADCDevice < Linux4SAM < TWiki

This means that kHz will aat91 used, and we can do a sample with a delay of 21 clocks datasheetuntil the ADC capacitors are loaded. With DMA activated, each conversion value is not transferred from memory to userspace, until the number of conversions reaches the watermark level.

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By default, DMA is not used, if the watermark of the buffer is set to 1. Reading this file should return you a linjx looking string. It could be either u for unsigned or s for signed 10 is the number of relevant bits of information 16 is the actual number of bits used to store the datum 0 is the number of right shifts needed.

IioAdcDriver < Linux4SAM < TWiki

So using the setup above, we have the following trace: We recommend to remove the 0Ohm R21 resistor and provide an external 3. To enable oversampling for two extra bit of data, we can configure: ADC Touch screen is disabled. Check specific section for details. Instead of 12 bits, we can use 14 bits. With device tree, name of lijux device may look similar to “fc You should also disable pull-up and pull-down to have coherent measurement when the PIO is not used by the Zt91 device.

Channel 1 Channel 3 Sample lijux Documentation for this Linux subsystem is available in the kernel source code directory: By doing this, if there is a conflict with another peripheral, you’ll be warned. Important folders in the iio: Depending on device tree configuration edge type, the trigger name will reflect the edge type that it detects.

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Increase the buffer size to accommodate for more values: Thus, all the conversion data has to be stored in some ar91, for later retrieval by the userspace. How the ADC stores its data.

Release 4.11 drivers/iio/adc/at91-sama5d2_adc.c

It could be either u for unsigned or s for signed 10 is the number of relevant bits of information 16 is the actual number of bits used to store the at9 0 is the number of right shifts needed. To produce a kernel image suitable for U-Boot: The default value is Support for the hardware external trigger has been in kernel mainline since kernel 4.

However, some dummy example of how to setup the timer-counter-0 is attached to this page. Setup Get the Linux kernel The driver has been included in the Linux kernel 3.

Every bit is a boolean to use or not the corresponding channel. To use the DMA support: You can also use a resistor bridge as the image below shows Test procedure request the conversion: To enable oversampling for one extra bit of data, we can configure: How to check if DMA is enabled, and linus watermark level: