This is an old revision of the document!
While this was requested to better understand how to control external power amplifiers for various software to implement push to talk (PTT), and ensure the PA was off during the Rx portion, this is good practice for any application which is just doing Rx or just doing Tx for best performance. Even you you are not concerned about controlling external devices, this may be a good read for some (just skip the GPO discussions).
There are two ways to implement General Purpose Output (GPO), Automatically (the easy way), or Software Controlled (which is handled later).
The AD9363 transceiver inside the ADALM-PLUTO includes an Enable State Machine (ENSM) that allows real time control over the current state of the device. The device can be placed in several different states during normal operation, including:
In this document, we will mainly focus on the Frequency Division Duplex (FDD) mode and the Time Division Duplex (TDD) Tx & Rx modes.
While the default settings are FDD mode (where Tx and Rx signal chains are always enabled), there are many use cases where TDD (Time Division Duplex) mode is beneficial. The ENSM has two control modes (1) SPI control and (2) pin control. If the TDD is a slotted system, where μsecond timing requirements must be met, pin control from a FPGA based state machine is normally used. When the TDD system is random, or push to talk, SPI control is possible. In SPI control mode, the ENSM is controlled asynchronously by writing to SPI registers to advance the current state to the next state. SPI control is considered asynchronous to the device or sample clock because the SPI clock can be derived from a different clock reference and can still function properly. The SPI control ENSM mode is recommended when real-time control of the synthesizers is not necessary.
The AD9363 also include 4
GPO_[0:3] General-Purpose Output pins. These are general-purpose logic output pins. These pins are designed to control other peripheral devices such as regulatorsswitches via the SPI bus, or they function as slaves for the internal AD9363 state machine. They can be configured to assert when the the Rx or Tx is active.
More information about the AD9363 can be found on the product page.
The power connected to the
VDD_GPO pin is 1.3 V The output voltage on the
GPO_[0:3] pins is expected to be
VDD_GPO × 0.8 (1.04 V) and
VDD_GPO (1.30 V). With an output current of 10 mA (typical). The off resistance of the GPO pins is 15 Ω. The on resistance of the GPO pins is 32 Ω. If you connect regulators or switches, it may need to be level shifted/have the drive strength increased to achieve the proper voltage control thresholds.
With the 1.3 V
VDD_GPO net, it is known/understood that the AUX_ADC and AUX_DAC will not be functional.
The schematic connects the
GPO_[0:3] pins to
GPO[0:3] nets and test points.
Just connect these
GPO[0:3] pins to whatever you need to control.
0is TDD mode,
1is FDD mode):
iio_attr -a -D ad9361-phy adi,frequency-division-duplex-mode-enable 0
GPO_0to assert when in Tx mode
iio_attr -a -D ad9361-phy adi,gpo0-slave-tx-enable 1
iio_attr -a -D ad9361-phy initialize 1
Verify the setup is in TDD mode, by checking the
ensm_mode_available attribute, and making sure it includes
tx and not
iio_attr -a -d ad9361-phy ensm_mode_available dev 'ad9361-phy', attr 'ensm_mode_available', value :'sleep wait alert rx tx pinctrl'
Then there is a run time configuration that is needed.
iio_attr -a -d ad9361-phy ensm_mode rx
iio_attr -a -d ad9361-phy ensm_mode tx
When you change from Rx mode to Tx mode, any of the four pins will assert/de-assert.
It should be noted that trying to capture a buffer (ie Rx) while in Tx mode will pause/hang until timed out. And sending a buffer (Tx) while in Rx mode will also pause/hang. Cancelling things will return.
There is a short bash script that shows how to use pin control from userspace: on GitHub
A small script on the Pluto SDR (or host) will demonstrate:
#!/bin/sh # Setup : Put into TDD mode, and setup GPO0 and GPO1 iio_attr -q -a -D ad9361-phy adi,frequency-division-duplex-mode-enable 0 iio_attr -q -a -D ad9361-phy adi,gpo0-slave-rx-enable 1 iio_attr -q -a -D ad9361-phy adi,gpo1-slave-tx-enable 1 iio_attr -q -a -D ad9361-phy initialize 1 while [ 1 ] ; do iio_attr -q -a -d ad9361-phy ensm_mode rx # capture buffer iio_attr -q -a -d ad9361-phy ensm_mode tx # transmit buffer done
by placing a scope on the GPO0 and GPO1 pins, you can see the levels switch, as the Pluto transitions between Receive and Transmit.
The Advanced Tab indicates how to control these in the IIO oscilloscope.
nμs, that can be done with the
gpo0-tx-delay-usattributes (which we don't cover here