Add tiny_relay variant files

- platformio.ini: Build configuration for tiny relay variant
- target.cpp/h: Hardware-specific implementation
- variant.h: Variant identification header

variants/tiny_relay/target.cpp

@@ -0,0 +1,82 @@
+#include "target.h"
+#include <Arduino.h>
+#include <helpers/ArduinoHelpers.h>
+
+TinyRelayBoard board;
+
+RADIO_CLASS radio = new STM32WLx_Module();
+
+WRAPPER_CLASS radio_driver(radio, board);
+
+static const uint32_t rfswitch_pins[] = {LORAWAN_RFSWITCH_PINS, RADIOLIB_NC, RADIOLIB_NC, RADIOLIB_NC};
+static const Module::RfSwitchMode_t rfswitch_table[] = {
+    {STM32WLx::MODE_IDLE, {LOW, LOW}},
+    {STM32WLx::MODE_RX, {HIGH, LOW}},
+    {STM32WLx::MODE_TX_LP, {LOW, HIGH}},
+    {STM32WLx::MODE_TX_HP, {LOW, HIGH}},
+    END_OF_MODE_TABLE,
+};
+
+VolatileRTCClock rtc_clock;
+SensorManager sensors;
+
+#ifndef LORA_CR
+#define LORA_CR 5
+#endif
+
+#ifndef STM32WL_TCXO_VOLTAGE
+// TCXO set to 0 for RAK3172
+#define STM32WL_TCXO_VOLTAGE 0
+#endif
+
+#ifndef LORA_TX_POWER
+#define LORA_TX_POWER 22
+#endif
+
+bool radio_init()
+{
+    //  rtc_clock.begin(Wire);
+
+    radio.setRfSwitchTable(rfswitch_pins, rfswitch_table);
+
+    int status = radio.begin(LORA_FREQ, LORA_BW, LORA_SF, LORA_CR, RADIOLIB_SX126X_SYNC_WORD_PRIVATE, LORA_TX_POWER, 16,
+                             STM32WL_TCXO_VOLTAGE, 0);
+
+    if (status != RADIOLIB_ERR_NONE) {
+        Serial.print("ERROR: radio init failed: ");
+        Serial.println(status);
+        return false; // fail
+    }
+
+#ifdef RX_BOOSTED_GAIN
+    radio.setRxBoostedGainMode(RX_BOOSTED_GAIN);
+#endif
+
+    radio.setCRC(1);
+
+    return true; // success
+}
+
+uint32_t radio_get_rng_seed()
+{
+    return radio.random(0x7FFFFFFF);
+}
+
+void radio_set_params(float freq, float bw, uint8_t sf, uint8_t cr)
+{
+    radio.setFrequency(freq);
+    radio.setSpreadingFactor(sf);
+    radio.setBandwidth(bw);
+    radio.setCodingRate(cr);
+}
+
+void radio_set_tx_power(uint8_t dbm)
+{
+    radio.setOutputPower(dbm);
+}
+
+mesh::LocalIdentity radio_new_identity()
+{
+    RadioNoiseListener rng(radio);
+    return mesh::LocalIdentity(&rng); // create new random identity
+}