I need to write one byte to my SPI peripheral and then read 3 bytes back while keeping CS asserted. My code is given below. Though my peripheral is responding, i'm reading zeroes in my code.

        unsigned char writeBuff[1] = { 0x1F };
        unsigned char readBuff[3]{ 42, 42, 42 };

        spi_ioc_transfer xfer[2]{};

        xfer[0].len = sizeof(writeBuff);
        xfer[0].tx_buf = (unsigned long)(writeBuff);

        xfer[1].len = sizeof(readBuff);
        xfer[1].rx_buf = (unsigned long)(readBuff);

        int status = ioctl(spiFd, SPI_IOC_MESSAGE(2), &xfer);
        if (status < 0) {
                printf("ERR: Failed to read %d\n", errno);
                exit(1);
        }

        for (auto i : readBuff) {
                std::cout << +i << " ";
        }
        std::cout << "\n";
        return 0;

How does SPI flash driver affect watchdog?

Wonder how onion does uboot development. Do they directly access the NOR flash ?

I've got JTAG to work with the board, but i can only control the CPU but not the internal flash. I tried compiling a uboot image that can be run from RAM, but did not have much luck with that. Has anyone used JTAG with onion before?

@crispyoz said in Are MAC addresses unique?:

I would suggest that while you could use the MAC address as a serial number, it is not a good idea

Why not? whats wrong with it?

I was planning to use the MAC address as a serial number. Are they unique? say across 2000 onions.

I would like to replace the uboot with my own custom one. Before i start working on it, i want to know how to recover if in case i accidentally brick it. Is the internal flash accessible over the SPI pins?

When powered directly, without the dev board, power consumption is as expected 141mA@3V3 when idling with WiFi off.

Like i mentioned, I'm using a 2SP module on the development board with power being measured at the input USB cable.