bcm2835 library default SPI clock divider / Bosch BMP280 / Haskell HPi

Question

I'm currently trying to access a Bosch BMP280 pressure sensor from Haskell using the HPi wrapper for the bcm2835 library.

I have no experience in handling SPI at all and as documentation is extremely brief / sparse, I had no success trying to troubleshoot the problem on my own.

As far as I understand, to read from the chip's registers, I have to clock out the address of the register to be read (with the first bit of this being replaced by a '0' to enter read mode)and then clock in as many bits as I want to read (by clocking out the corresponding number of Bits / Word8's of zeros while returning the bits being clocked in at the same time). In code (following the spitest.hs from the HPi GitHub repo):

import System.RaspberryPi.GPIO
import Control.Concurrent
import Control.Monad
import Data.Bits
import qualified Data.ByteString as BS
import Data.Word

main = withGPIO . withSPI $ do
    chipSelectSPI CS0   --set the Chip select pin to the CS0 pin
    setChipSelectPolaritySPI CS0 False --The BMP chip needs CS to be pulled low
    setDataModeSPI (False,False)
    transferManySPI [244,47] -- write 0xF4 = 244 settings 00101111 = 47
    transferManySPI [245,160] -- write 0xF5 = 245 settings 10100000 = 160
    threadDelay 10000
    printReadout

printReadout :: IO()
printReadout = do
    transferManySPI [122,0] >>= (print) -- read 0xFA = 0x7A = 122

Is that correct? With this code I get nothing than [0,0] back from the sensor.

Starting to guess what the problem might be, as the bcm2835SPIClockDivider enumeration type from the library seems not to be handled in any way in HPi, I wonder about if there is a default clock divider / clock speed used by the library and if it possibly exceeds the maximum of 10 MHz mentioned in the sensor's manual. Is that the case?

bcm2835 library default SPI clock divider / Bosch BMP280 / Haskell HPi

0 Answers0