E3x0/X3x0 GPIO API

Table of Contents

• The E3x0/X3x0 Front Panel GPIO
  • X3x0 Front Panel GPIO
    • Connector
    • Pin Mapping
  • E3x0 Internal GPIO
    • Connector
  • Explaining ATR
  • An Example

The E3x0/X3x0 Front Panel GPIO

The E3x0/X3x0 are the first USRP devices to offer an auxiliary GPIO connection on the motherboard itself (independent of the daughterboards). These GPIO pins are controlled directly by the FPGA, where they are controlled by an ATR (Automatic Transmit / Receive). This allows them to be toggled simultaneously with other radio-level changes (e.g., enabling or disabling a TX or RX mixer).

X3x0 Front Panel GPIO

The GPIO port is not meant to drive big loads. You should not try to source more than 5mA per pin.

The +3.3V is for ESD clamping purposes only and not designed to deliver high currents.

Connector

X3x0 GPIO Connectors

Pin Mapping

• Pin 1: +3.3V
• Pin 2: Data[0]
• Pin 3: Data[1]
• Pin 4: Data[2]
• Pin 5: Data[3]
• Pin 6: Data[4]
• Pin 7: Data[5]
• Pin 8: Data[6]
• Pin 9: Data[7]
• Pin 10: Data[8]
• Pin 11: Data[9]
• Pin 12: Data[10]
• Pin 13: Data[11]
• Pin 14: 0V
• Pin 15: 0V

E3x0 Internal GPIO

Connector

E3x0 GPIO Connector

Pin Mapping

• Pin 1: +3.3V
• Pin 2: Reserved
• Pin 3: Data[5]
• Pin 4: Reserved
• Pin 5: Data[4]
• Pin 6: Data[0]
• Pin 7: Data[3]
• Pin 8: Data[1]
• Pin 9: 0V
• Pin 10: Data[2]

Explaining ATR

ATR works by defining the value of the GPIO pins for certain states of the radio. This is the "automatic" part of it. For example, you can tell UHD that when the radio is transmitting and receiving (full duplex), GPIO6 should be high, but when it is only transmitting, GPI06 should be low. This state machine is set up using a series of GPIO attributes, with paired values and a mask, which you will want to define for the GPIO pins you intend to use. To set up the ATR, you use uhd::usrp::multi_usrp::set_gpio_attr().

• CTRL: Is this pin controlled by ATR (automatic), or by manual control only?
• DDR: "Data Direction Register" - defines whether or not a GPIO is an output or an input.
• OUT: Manually set the value of a pin (only to be used in non-ATR mode).
• ATR_0X: The status of the pins when the radio is idle.
• ATR_RX: The status of the pins when the radio is only receiving**.
• ATR_TX: The status of the pins when the radio is only transmitting**.
• ATR_XX: The status of the pins when the radio is in full-duplex** mode.

The counterpart to setting the ATR (the "getter"), is called uhd::usrp::multi_usrp::get_gpio_attr(). t has the exact same attributes as above, and has one more:

• READBACK: Readback the GPIOs marked as inputs.

An Example

The front panel X3x0 GPIO bank is enumerated in the motherboard property tree (<mb_path>/gpio/FP0/\*), the E3x0 internal GPIO bank as (<mb_path>/gpio/INT0/\) and so are easily accessible through the standard uhd::usrp::multi_usrp UHD interface.

You can discover this using the uhd::usrp::multi_usrp::get_gpio_banks() function. This will tell you that there is a GPIO bank on your X3x0 called "FP0" (for E3x0 this will be called "INT0"). This is the bank we want to set-up.

Let's say we want to use GPIO6 for an external amp. We want it to be automatically controlled by ATR as an output, and we want it to be high when we are transmitting, and low in all other cases. We are also using GPIO4, which we want to control manually, as an output. We can set this up with the following code:

// set up our masks, defining the pin numbers
#define AMP_GPIO_MASK   (1 << 6)
#define MAN_GPIO_MASK   (1 << 4)

#define ATR_MASKS       (AMP_GPIO_MASK | MAN_GPIO_MASK)

// set up our values for ATR control: 1 for ATR, 0 for manual
#define ATR_CONTROL     (AMP_GPIO_MASK & ~MAN_GPIO_MASK)

// set up the GPIO directions: 1 for output, 0 for input
#define GPIO_DDR        (AMP_GPIO_MASK & ~MAN_GPIO_MASK)

// assume an existing USRP device handle, called "usrp_x300"

// now, let's do the basic ATR setup
usrp_x300->set_gpio_attr("FP0", "CTRL", ATR_CONTROL, ATR_MASKS);
usrp_x300->set_gpio_attr("FP0", "DDR", GPIO_DDR, ATR_MASKS);

// let's manually set GPIO4 high
usrp_x300->set_gpio_attr("FP0", "OUT", 1, MAN_GPIO_MASK);

// finally, let's set up GPIO6 as we described above
usrp_x300->set_gpio_attr("FP0", "ATR_0X", 0, AMP_GPIO_MASK);
usrp_x300->set_gpio_attr("FP0", "ATR_RX", 0, AMP_GPIO_MASK);
usrp_x300->set_gpio_attr("FP0", "ATR_TX", 0, AMP_GPIO_MASK);
usrp_x300->set_gpio_attr("FP0", "ATR_XX", 0, AMP_GPIO_MASK);

After the above code is run, the ATR in the FPGA will automatically control GPIO6, as we have described, based on the radio state, and we have direct manual control over GPIO4.

The following example has been modified to work with he E3x0's internal GPIO bank, where the controlled GPIO is now GPIO3 instead of GPIO6.

// set up our masks, defining the pin numbers
#define AMP_GPIO_MASK   (1 << 3)
#define MAN_GPIO_MASK   (1 << 4)

#define ATR_MASKS       (AMP_GPIO_MASK | MAN_GPIO_MASK)

// set up our values for ATR control: 1 for ATR, 0 for manual
#define ATR_CONTROL     (AMP_GPIO_MASK & ~MAN_GPIO_MASK)

// set up the GPIO directions: 1 for output, 0 for input
#define GPIO_DDR        (AMP_GPIO_MASK & ~MAN_GPIO_MASK)

// assume an existing USRP device handle, called "usrp_e300"

// now, let's do the basic ATR setup
usrp_e300->set_gpio_attr("INT0", "CTRL", ATR_CONTROL, ATR_MASKS);
usrp_e300->set_gpio_attr("INT0", "DDR", GPIO_DDR, ATR_MASKS);

// let's manually set GPIO4 high
usrp_e300->set_gpio_attr("INT0", "OUT", (1 << 4), MAN_GPIO_MASK);

// finally, let's set up GPIO6 as we described above
usrp_e300->set_gpio_attr("INT0", "ATR_0X", 0, AMP_GPIO_MASK);
usrp_e300->set_gpio_attr("INT0", "ATR_RX", 0, AMP_GPIO_MASK);
usrp_e300->set_gpio_attr("INT0", "ATR_TX", 0, AMP_GPIO_MASK);
usrp_e300->set_gpio_attr("INT0", "ATR_XX", 0, AMP_GPIO_MASK);

After the above code is run, the ATR in the FPGA will automatically control GPIO3, as we have described, based on the radio state, and we have direct manual control over GPIO4.