[rtl872x] Implement WiFi.selectAntenna

[scott-brust]

Problem

WiFi.selectAntenna() is not implemented for P2

Solution

On P2, BLE and WiFi share the same physical antenna, so use selectAntenna() from radio_common.cpp

Steps to Test

Use test app below to verify antenna switches

Example App

#include "Particle.h"

SYSTEM_MODE(AUTOMATIC);
SYSTEM_THREAD(ENABLED);

SerialLogHandler logHandler(LOG_LEVEL_ERROR,
{
    { "app", LOG_LEVEL_ALL },
});

String anntena_names[] = {"Internal", "External", "", "Automatic"};

void setup() {
    
}
 
void loop() {
    if (!Serial.available()) {
        return;
    }

    while (Serial.available()) {
        char c = Serial.read();
        Log.info("Got %c", c);
        int result = 0;
        if (c == 'i') {
            result = WiFi.selectAntenna(ANT_INTERNAL);
        }
        else if (c == 'e') {
            result = WiFi.selectAntenna(ANT_EXTERNAL);
        }
        else if (c == 'a') {
            result = WiFi.selectAntenna(ANT_AUTO);
        }
        else if (c == 'n') {
            result = WiFi.selectAntenna(ANT_NONE);
        }

        String antenna_name = "";
        WLanSelectAntenna_TypeDef antenna = WiFi.getAntenna();
        if (antenna <= ANT_AUTO) {
            antenna_name = anntena_names[(int)antenna];
        }

        Log.info("WiFi.selectAntenna result: %d now using %s antenna", result, antenna_name.c_str());

        if (result == SYSTEM_ERROR_NONE) {
            WiFiAccessPoint aps[20];
            int found = WiFi.scan(aps, 20);
            for (int i=0; i<found; i++) {
                WiFiAccessPoint& ap = aps[i];
                Log.info("ssid=%s security=%d channel=%d rssi=%d", ap.ssid, (int)ap.security, (int)ap.channel, ap.rssi);
            }    
        }
    }
}

Test output with no external antenna

0000012710 [app] INFO: Got n
0000012717 [app] INFO: WiFi.selectAntenna result: -120 now using Automatic antenna
0000017798 [app] INFO: Got i
0000017968 [app] INFO: WiFi.selectAntenna result: 0 now using Internal antenna
0000022089 [app] INFO: ssid=derp security=3 channel=9 rssi=-47
0000022105 [app] INFO: ssid=derp5 security=3 channel=153 rssi=-55
0000025071 [app] INFO: Got e
0000025238 [app] INFO: WiFi.selectAntenna result: 0 now using External antenna
0000029357 [app] INFO: ssid=derp5 security=3 channel=153 rssi=-70
0000029374 [app] INFO: ssid=derp security=3 channel=9 rssi=-88
0000033136 [app] INFO: Got a
0000033307 [app] INFO: WiFi.selectAntenna result: 0 now using Automatic antenna
0000037429 [app] INFO: ssid=derp security=3 channel=9 rssi=-47
0000037444 [app] INFO: ssid=derp5 security=3 channel=153 rssi=-55

Switching from Auto / Internal to external shows a drop in RSSI

---

Completeness

• User is totes amazing for contributing!
• Contributor has signed CLA (Info here)
• Problem and Solution clearly stated
• Run unit/integration/application tests on device
• Added documentation
• Added to CHANGELOG.md after merging (add links to docs and issues)

[avtolstoy]

The setting is already saved in DCT (DCT_RADIO_ANTENNA_OFFSET). Just needs to be exposed in radio_common stuff.

[scott-brust]

Should we validate the DCT data or just return it if its present?

[avtolstoy]

Nit/style: radio_antenna_type* antenna, same above

[avtolstoy]

I'd do exactly the same thing as currently done in initRadioAntenna() and return default normally unless dct read value is exactly INTERNAL or EXTERNAL and replace that block with getRadioAntenna() so that we don't have duplicate logic.