Introduction

LOS Link is the interface that provides RC channel data which is how we figure out the stick inputs from the RC controller. Traditionally, PPM (Pulse Position Modulation) is used to but there are other methods of communicating this data such as TBS CROSSFIRE or SBUS that we are looking into.

Data

The data coming through LOS Link is quite trivial, all one would want to know is the percentage of each RC channel and a signal strength. As of Nov 24, 2022, the data structure returned by LOS Link looks like the following:

typedef struct LosLinkRx_t{
  uint8_t rssi;
  uint8_t rx_channels[NUM_RX_CHANNELS];
};

Where the rssi represents the signal strength and the rx_channels array holds the position of each input from the RC controller, both represented as a percentage form 0-100%. NUM_RX_CHANNELS is a const that holds the number of active channels.

Using the Interface

LOS Link is not too complex as it essentially directly calls the appropriate RcReceiver driver on each of the active channels, based on what was configured in the config.h files.

LOS Link, along with all the other LOS interfaces, is implemented as a singleton, meaning the only way to use the interface is to call the getInstance() function to retrieve the singleton instance then make the appropriate calls.

Currently, the only public function exposed from LOS Link is LosLinkRx_t getRx(uint8_t instance) where instance is the index of the RcReceiver in the array holding all RcReceiver instances in the config.h and it returns the data structure defined above. instance is an optional parameter as is defaulted to index 0 because for a long time, there was only ever 1 instance of the PPM driver, but that may change in the future when we want multiple stream of RC channel data from different sources.

Related Drivers

LOS Link only uses 1 set of drivers, RcReceiver.

RcReceiver is the base class that encompasses the related derived classes, currently only PPMChannel but possibly a CROSSFIRE and SBUS class in the future. The main virtual function that is to be implemented by all RcReceiver derived classes/drivers is the uint8_t GetResult(uint8_t channel) which should return the percentage of the RC channel index passed in.