Issue with SPI (Serial Port Comm), stuck on ioctl()

I'm trying to access a SPI sensor using the SPIDEV driver but my code gets stuck on IOCTL. I'm running embedded Linux on the SAM9X5EK (mounting AT91SAM9G25). The device is connected to SPI0. I enabled CONFIG_SPI_SPIDEV and CONFIG_SPI_ATMEL in menuconfig and added the proper code to the BSP file: ``` static struct spi_board_info spidev_board_info[] { { .modalias = "spidev", .max_speed_hz = 1000000, .bus_num = 0, .chips_select = 0, .mode = SPI_MODE_3, }, ... }; spi_register_board_info(spidev_board_info, ARRAY_SIZE(spidev_board_info)); ``` 1MHz is the maximum accepted by the sensor, I tried 500kHz but I get an error during Linux boot (too slow apparently). .bus_num and .chips_select should correct (I also tried all other combinations). SPI_MODE_3 I checked the datasheet for it. I get no error while booting and devices appear correctly as /dev/spidevX.X. I manage to open the file and obtain a valid file descriptor. I'm now trying to access the device with the following code (inspired by examples I found online). ``` #define MY_SPIDEV_DELAY_USECS 100 // #define MY_SPIDEV_SPEED_HZ 1000000 #define MY_SPIDEV_BITS_PER_WORD 8 int spidevReadRegister(int fd, unsigned int num_out_bytes, unsigned char *out_buffer, unsigned int num_in_bytes, unsigned char *in_buffer) { struct spi_ioc_transfer mesg[2] = { {0}, }; uint8_t num_tr = 0; int ret; // Write data mesg[0].tx_buf = (unsigned long)out_buffer; mesg[0].rx_buf = (unsigned long)NULL; mesg[0].len = num_out_bytes; // mesg[0].delay_usecs = MY_SPIDEV_DELAY_USECS, // mesg[0].speed_hz = MY_SPIDEV_SPEED_HZ; mesg[0].bits_per_word = MY_SPIDEV_BITS_PER_WORD; mesg[0].cs_change = 0; num_tr++; // Read data mesg[1].tx_buf = (unsigned long)NULL; mesg[1].rx_buf = (unsigned long)in_buffer; mesg[1].len = num_in_bytes; // mesg[1].delay_usecs = MY_SPIDEV_DELAY_USECS, // mesg[1].speed_hz = MY_SPIDEV_SPEED_HZ; mesg[1].bits_per_word = MY_SPIDEV_BITS_PER_WORD; mesg[1].cs_change = 1; num_tr++; // Do the actual transmission if(num_tr > 0) { ret = ioctl(fd, SPI_IOC_MESSAGE(num_tr), mesg); if(ret == -1) { printf("Error: %d\n", errno); return -1; } } return 0; } ``` Then I'm using this function: ``` #define OPTICAL_SENSOR_ADDR "/dev/spidev0.0" ... int fd; fd = open(OPTICAL_SENSOR_ADDR, O_RDWR); if (fd<=0) { printf("Device not found\n"); exit(1); } uint8_t buffer1[1] = {0x3a}; uint8_t buffer2[1] = {0}; spidevReadRegister(fd, 1, buffer1, 1, buffer2); ``` When I run it, the code get stuck on IOCTL! I did this way because, in order to read a register on the sensor, I need to send a byte with its address in it and then get the answer back without changing CS (however, when I tried using write() and read() functions, while learning, I got the same result, stuck on them). I'm aware that specifying .speed_hz causes a ENOPROTOOPT error on Atmel (I checked spidev.c) so I commented that part. Why does it get stuck? I though it can be as the device is created but it actually doesn't "feel" any hardware. As I wasn't sure if hardware SPI0 corresponded to bus_num 0 or 1, I tried both, but still no success (btw, which one is it?). UPDATE: I managed to have the SPI working! Half of it.. MOSI is transmitting the right data, but CLK doesn't start... any idea?