Update pico_sdk.md to reflect changes to SPI with user-specified pins

[matt-walker0]

Hi,

Updated some of my code that uses the RF24 library, guess there's been some changes in the meantime as the previous code no longer compiles. Quick look suggests now the SPI needs be declared seperately and cannot be reference just by importing RF24 and using spi.begin

Previous code:

    spi.begin(spi_bus, sck_pin, tx_pin, rx_pin);

    if(radio.begin(&spi, ce_pin, csn_pin) == false) {     // Setup and configure rf radio
        return(false);
    }

Seems to be fixed by declaring a SPI object outside the function that initialises the radio. (could be a better way to do this?)

SPI spi;

Hence have suggested a change to documentation to reflect this.

[2bndy5]

Please use latest commit on master. I fixed this problem in 557d165

[2bndy5]

Oh, I see what you mean now.

Yes, to change the pin numbers from their defaults, you need to declare an SPI object and pass it to RF24::begin().

Before, this wasn't needed because the wrapping SPI class had only static functions. I never liked this approach because it hides the declaration from the user. The way it is now should be clearer to C++ learners.

[matt-walker0]

Cheers, it was more a case of it fixed things on my end, but indeed does make it clearer for those not using default pins.