Radio Driver Operation

The LMIC radio driver operates asynchronously. Operations are started by calling the os_radio() function with a parameter describing the operation to be performed.

Various parameters in the LMIC structure are as input to control the operation; others are updated to return results.

os_radio(RADIO_RST)

The radio is reset, and put to sleep. This operation is synchronous.

os_radio(RADIO_TX)

A frame is transmitted. The parameters are given in "Common parameters" and "Transmit parameters" below.

When the operation completes, LMIC.osjob is scheduled.

os_radio(RADIO_RX)

A single frame is received at the specified time, and the radio is put back to sleep if no frame is found.

When the operation completes, LMIC.osjob is scheduled.

os_radio(RADIO_RXON)

The radio is placed in continuous receive mode. If a frame is received, LMIC.osjob is scheduled. Continuous receive is explicitly canceled by calling os_radio(RADIO_RST) or implicitly by calling any other radio function.

This operation is not supported in FSK mode.

os_radio(RADIO_RXON_C)

This operation is identical to os_radio(RADIO_RXON), but redundant calls are suppressed. That is, if the radio is already in receive mode, the radio stays in receive mode without any change in state. In contrast, RADIO_RXON expects the radio to be idle, and will issue an assertion failure if the radio is in any other state.

os_radio(RADIO_TX_AT)

This is like os_radio(RADIO_TX), but the transmission is scheduled at LMIC.txend.

Common parameters

LMIC.radio.rps (IN)

This is the "radio parameter setting", and it encodes several radio settings.

Spreading factor: FSK or SF7..12
Bandwidth: 125, 250 or 500 kHz
Coding Rate: 4/5, 4/6, 4/7 or 4/8.
CRC enabled/disabled
Implicit header mode on/off. (If on, receive length must be known in advance.)

LMIC.radio.freq (IN)

This specifies the frequency, in Hertz.

LMIC.saveIrqFlags (OUT)

Updated for LoRa operations only; the IRQ flags at the time of interrupt.

LMIC.radio.pRadioDoneJob (IN/OUT)

When asynchronous operations complete, LMIC.radio.pRadioDoneJob->func is used as the callback function, and LMIC.radio.pRadioDoneJob is used to schedule the work.

Transmit parameters

LMIC.radio.txpow (IN)

This specifies the transmit power in dBm.

LMIC.radio.pFrame[] (IN)

The array of data to be sent.

LMIC.radio.datalen (IN)

The length of the array to be sent.

LMIC.txend (IN, OUT)

For RADIO_TX_AT, an input parameter, for the scheduled TX time.

For all transmissions, updated to the OS time at which the TX end interrupt was recognized.

LMIC.lbt_ticks (IN)

How long to monitor for LBT, in OS ticks.

LMIC.lbt_dbmax (IN)

Maximum RSSI on channel before transmit.

Receive parameters

LMIC.radio.pFrame[] (OUT)

Filled with data received.

LMIC.radio.dataLen (OUT)

Set to number of bytes received in total.

LMIC.radio.rxtime (IN/OUT)

Input: When to start receiving, in OS tick time. Only used for os_radio(RADIO_RX); not used for continuous receive.

Output: time of RXDONE interrupt. (Note: FSK timeout doesn't currently set this cell on RX timeout.)

LMIC.radio.rxsyms (IN)

The timeout in symbols. Only used for os_radio(RADIO_RX); not used for continuous receive.

LMIC.radio.flags (IN)

If the bit LMIC_RADIO_FLAGS_NO_RX_IQ_INVERSION is set, disable IQ inversion during receive.

LMIC.snr (OUT)

Set to SNR * 4 after LoRa receive. (Set to 0 for FSK receive.)

LMIC.rssi (OUT)

Set to RSSI + RSSI_OFF after LoRa receive. (Set to 0 for FSK receive; RSSI_OFF is 64.) You must subtract RSSI_OFF from LMIC.rssi to get the RSSI in dB.