I’m currently trying to make a NRF24L01 module work by using Java. I found this library that makes use of the JNI, but I can’t get it to work.

When I try to run the provided example code the Raspberry Pi just hangs and the CPU rises to 100% after (or rather while) running rf24.begin().

I digged a little bit into the code and found out that the reason it hangs is due to an endless while loop inside the bcm2835_spi_transfernb() function of this file.

The function is the following:

void bcm2835_spi_transfernb(char* tbuf, char* rbuf, uint32_t len)
{
    volatile uint32_t* paddr = bcm2835_spi0 + BCM2835_SPI0_CS/4;
    volatile uint32_t* fifo = bcm2835_spi0 + BCM2835_SPI0_FIFO/4;
    uint32_t TXCnt=0;
    uint32_t RXCnt=0;

    // This is Polled transfer as per section 10.6.1
    // BUG ALERT: what happens if we get interupted in this section, and someone else
    // accesses a different peripheral?

    // Clear TX and RX fifos
    bcm2835_peri_set_bits(paddr, BCM2835_SPI0_CS_CLEAR, BCM2835_SPI0_CS_CLEAR);

    // Set TA = 1
    bcm2835_peri_set_bits(paddr, BCM2835_SPI0_CS_TA, BCM2835_SPI0_CS_TA);

    // Use the FIFO's to reduce the interbyte times
    while((TXCnt < len)||(RXCnt < len))
    {
        // TX fifo not full, so add some more bytes
        while( (bcm2835_peri_read(paddr) & BCM2835_SPI0_CS_TXD )  && (TXCnt < len )  && !(bcm2835_peri_read(paddr) & BCM2835_SPI0_CS_RXR) )
        {
           bcm2835_peri_write_nb(fifo, tbuf[TXCnt]);
           TXCnt++;

        }   
        //Rx fifo not empty, so get the next received bytes     
        while(((bcm2835_peri_read(paddr) & BCM2835_SPI0_CS_RXD))&&( RXCnt < len )){        
           rbuf[RXCnt] = bcm2835_peri_read_nb(fifo);
           RXCnt++;    
        }
    }
    while(! (bcm2835_peri_read(paddr) & BCM2835_SPI0_CS_DONE) ){}
    if(TXCnt == len){ bcm2835_peri_set_bits(paddr, 0, BCM2835_SPI0_CS_TA);}
}

The problem is that the two while loops inside the outer while loop are never entered and therefore the exit-condition cannot occur turning this into an endless while loop.

Unfortunately I have no idea why that happens. Is it possible that this is due to a SPI related problem, like me forgetting to setup something? I did enable the SPI interface and validated it multiple times and also tested it. It seems to be working correctly. I also checked my wiring multiple times and I’m confident that its correct.

I would appreciate a little input, since I am really lost regarding this right now.