GPIO¶
The USRP E320 implements an 8-bit GPIO port. Each bit is routed to a dedicated pin in the Zynq PL. The GPIO port uses a mini-HDMI (HDMI Type C) jack on the E320 back panel.
The 802.11 MAC/PHY design uses the GPIO port for debug I/O. The GPIO pins are connected to the wlan_userio core which implements the necessary logic to use each GPIO pin as an input or output. The wlan_userio core supports reading GPIO inputs from software or hardware, and supports setting GPIO outputs from software or hardware. By default the 8 GPIO pins are configured as software-controlled outputs.
Pinout¶
The USRP E320 hardware connects the 19 pins of the mini-HDMI jack to the 8 GPIO signals plus ground and power. The table below lists the E320 nets connected to each mini-HDMI pin, and the corresponding pin number when a mini-HDMI (Type C) to HDMI (Type A) adapter is used.
The GPIO_n signals are 3.3v I/O. The direction (input/output) is configured per-pin in the 802.11 MAC software.
| E320 Net | mini-HDMI Pin (Type C) | HDMI Pin (Type A) |
|---|---|---|
| GPIO_0 | 8 | 7 |
| GPIO_1 | 9 | 9 |
| GPIO_2 | 11 | 10 |
| GPIO_3 | 12 | 12 |
| GPIO_4 | 14 | 13 |
| GPIO_5 | 15 | 15 |
| GPIO_6 | 16 | 16 |
| GPIO_7 | 17 | 14 |
| GND | 1 | 2 |
| GND | 3 | 3 |
| GND | 4 | 5 |
| GND | 6 | 6 |
| GND | 7 | 8 |
| GND | 10 | 11 |
| GND | 13 | 17 |
| GND | 19 | 19 |
| +3.3v | 18 | 18 |
| – | 2 | 1 |
| – | 5 | 4 |
802.11 Debug Outputs¶
The 802.11 MAC/PHY design drives real-time MAC and PHY status signals to debug outputs. On hardware platforms with debug headers these status outputs can be probed with an oscillosope to observe MAC/PHY state in real-time.
The reference 802.11 FPGA design for the USRP E320 connects the 8 LSB of the MAC/PHY debug bus to the E320 GPIO port. Observing these signals with a scope requires external equipment to access the GPIO pins.
Cable Recommendations¶
To observe MAC/PHY debug signals we recommend using a cable and breakout board to access the GPIO signals:
- A mini-HDMI (Type C) to HDMI (Type A) cable (https://www.adafruit.com/product/2775)
- HDMI socket breakout board (https://www.adafruit.com/product/3121)
Other combinations should work, like a mini-HDMI to HDMI adapter and an HDMI plug breakout (https://www.adafruit.com/product/3119).
In both cases the HDMI breakout boards enumerate pins using the Type A connector pin numbers. Refer to the table above for the mapping of Type A pins to USRP E320 GPIO signals.
An oscilloscope probe ground lead can use the HDMI pins tied to ground (GND in the table above) on the E320 board.