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In my previous project I have used spidev in order to work with ADC, and in python script I could have:

spi = spidev.SpiDev()
spi.open(0,0)
...
adc = spi.xfer2([1,(8+channel)<<4,0])

Now I'm trying to work with pigpio library (to avoid the permission demands) but I'm not really sure how to use pigpio's spi_open and spi_xfer functions. Looks like they take more input arguments than spi.open and spi.xfer2. Can someone explain to me what these arguments are - in some analogy with my previous approach with spidev? Thanks a lot.

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spi_open

You only need to specify the channel and bit rate. The flags should normally be left as 0. The call returns a handle (a small number >=0) which is passed to the other SPI functions.

h = spi_open(0, 1000000) # get handle for SPI channel 0 at 1000000 bits per second.

spi_xfer

Ypu specify the handle (returned by spi_open) and the data to send. The number of bytes received and the bytes themselves are returned.

adc_channel = 0

count, data = spi_xfer(h, [1,(8+adc_channel)<<4,0])

Send three bytes to the SPI device defined by handle h. The individual bytes are 1, (8+adc_channel)<<4, and 0.

count will be 3 (the number of bytes received is always the same as the number of bytes send except for errors) and data will be a list of three bytes (data[0], data[1], and data[2]).

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