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I am trying to read MCP3201 with 44100 samples per second. The chip has top clock frequency of 1Mhz, which should be sufficient for 62500 two-byte samples per second.

sampnumb = 44100

spi = spidev.SpiDev()
spi.open(0,0)
spi.max_speed_hz = 125000000

for i in range(sampnumb):
    dat = spi.xfer2([0x00, 0x00])

It actually takes almost 2s to read as many samples. Using 976000 for max_speed_hz makes it even slower.

Are there any ways to make sampling faster in Python? If not, is this possible to achieve fast sampling any other way?

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1 Answer 1

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You need to write your software in another language to achieve the speed you are after.

The obvious choice is C.

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  • integrate top level python calls into low level c calls with cython. don't do a big for loop in python- instead loop in c but tell c the number to loop via python.
    – Abel
    Commented Jan 31, 2022 at 12:39
  • @Abel I intend to use ctypes since I already have experience with that.
    – Pygmalion
    Commented Jan 31, 2022 at 13:34
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    With a simple C script (ioctl(fd_spi, SPI_IOC_MESSAGE(1), &spi); spi.rx_buf = spi.rx_buf + 2;) I could get about 15k sampling. Unfortunately sampling is not very consistent, which means that FFT of the sound is rather noisy. Any ideas for improvement?
    – Pygmalion
    Commented Jan 31, 2022 at 16:15
  • Use pigpio. Use a faster Pi (you appear to be using an old one).
    – joan
    Commented Jan 31, 2022 at 16:33
  • You are doing something wrong if you are getting slower rates in C compared to Python. Have you set the SPI bit rate in your C code?
    – joan
    Commented Jan 31, 2022 at 16:49

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