Hi everyone, I built a project that demonstrates how to use the front-panel GPIO pins of the USRP X310 to emulate an SPI interface. The SPI communication leverages UHD timed commands and RFNoC blocks to drive GPIO signals at precise intervals. But there is a slow performance when I read GPIO values. If I comment the blue part, the code can generate SCK and SDO up to 2MHz. But if I add the function of reading gpio, the output clock is slowed down to 100Hz.
This is weird. Anyone know why? The code is open source at https://github.com/cjhonlyone/uhd_gpio_spi. int UhdGpioSpi::write_and_read(uint8_t* write_buffer, uint8_t* read_buffer, uint32_t length) { double spi_period = 1.0 / spi_frequency; radio_ctrl->clear_command_time(0); uhd::time_spec_t time = radio_ctrl->get_time_now() + uhd::time_spec_t(0.05); time = time + uhd::time_spec_t(spi_period); radio_ctrl->set_command_time(time, 0); radio_ctrl->set_gpio_attr("FP0", "OUT", (~SDO_MASK) & (~SCS_MASK) & (cpol ? 0xffffffff : (~SCK_MASK))); for (uint32_t i = 0; i < length; i++) { for (uint32_t j = 0; j < 8; j++) { time = time + uhd::time_spec_t(0.5 * spi_period); radio_ctrl->set_command_time(time, 0); if ((cpha & cpol) || ((!cpha) & (!cpol))) { // SCK = 0, SCS = 0 radio_ctrl->set_gpio_attr("FP0", "OUT", (write_buffer[i] & (1 << (7 - j))) ? (~SCS_MASK) & (~SCK_MASK) : ((~SCS_MASK) & (~SCK_MASK) & (~SDO_MASK))); } else { // SCK = 1, SCS = 0 radio_ctrl->set_gpio_attr("FP0", "OUT", (write_buffer[i] & (1 << (7 - j))) ? (~SCS_MASK) : (~SCS_MASK) & (~SDO_MASK)); } time = time + uhd::time_spec_t(0.5 * spi_period); radio_ctrl->set_command_time(time, 0); if ((cpha & cpol) || ((!cpha) & (!cpol))) { // SCK = 1, SCS = 0 radio_ctrl->set_gpio_attr("FP0", "OUT", (write_buffer[i] & (1 << (7 - j))) ? (~SCS_MASK) : (~SCS_MASK) & (~SDO_MASK)); } else { // SCK = 0, SCS = 0 radio_ctrl->set_gpio_attr("FP0", "OUT", (write_buffer[i] & (1 << (7 - j))) ? (~SCS_MASK) & (~SCK_MASK) : ((~SCS_MASK) & (~SCK_MASK) & (~SDO_MASK))); } // radio_ctrl->set_command_time(time, 0); // if (radio_ctrl->get_gpio_attr("FP0", "READBACK") & SDI_MASK) // read_buffer[i] |= (1 << (7 - j)); // if (j < 7) read_buffer[i] <<= 1; } // nop time = time + uhd::time_spec_t(0.5*spi_period); radio_ctrl->set_command_time(time, 0); radio_ctrl->set_gpio_attr("FP0", "OUT", (~SDO_MASK) & (~SCS_MASK) & (cpol ? 0xffffffff : (~SCK_MASK))); } time = time + uhd::time_spec_t(spi_period); radio_ctrl->set_command_time(time, 0); radio_ctrl->set_gpio_attr("FP0", "OUT", SCS_MASK | (cpol ? SCK_MASK : 0x00000000)); return 0; }
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