ardupilot/libraries/AP_HAL/UARTDriver.h

#pragma once

#include <stdint.h>

#include "AP_HAL_Namespace.h"
#include "utility/BetterStream.h"

#ifndef HAL_UART_STATS_ENABLED
#define HAL_UART_STATS_ENABLED !defined(HAL_NO_UARTDRIVER)

#endif

class ExpandingString;

/* Pure virtual UARTDriver class */
class AP_HAL::UARTDriver : public AP_HAL::BetterStream {
private:
    // option bits for port
    uint16_t _last_options;

public:
    UARTDriver() {}
    /* Do not allow copies */
    UARTDriver(const UARTDriver &other) = delete;
    UARTDriver &operator=(const UARTDriver&) = delete;

    // begin() implicitly clears rx/tx buffers, even if the port was already open (unless the UART is the console UART)
    virtual void begin(uint32_t baud) = 0;
    virtual void begin_locked(uint32_t baud, uint32_t key) { begin(baud); }

	/// Extended port open method
	///
	/// Allows for both opening with specified buffer sizes, and re-opening
	/// to adjust a subset of the port's settings.
	///
	/// @note	Buffer sizes greater than ::_max_buffer_size will be rounded
	///			down.
	///
	/// @param	baud		Selects the speed that the port will be
	///						configured to.  If zero, the port speed is left
	///						unchanged.
	/// @param rxSpace		Sets the receive buffer size for the port.  If zero
	///						then the buffer size is left unchanged if the port
	///						is open, or set to ::_default_rx_buffer_size if it is
	///						currently closed.
	/// @param txSpace		Sets the transmit buffer size for the port.  If zero
	///						then the buffer size is left unchanged if the port
	///						is open, or set to ::_default_tx_buffer_size if it
	///						is currently closed.
	///
    virtual void begin(uint32_t baud, uint16_t rxSpace, uint16_t txSpace) = 0;
    virtual void end() = 0;
    virtual void flush() = 0;
    virtual bool is_initialized() = 0;
    virtual void set_blocking_writes(bool blocking) = 0;
    virtual bool tx_pending() = 0;

    // lock a port for exclusive use. Use a key of 0 to unlock
    virtual bool lock_port(uint32_t write_key, uint32_t read_key) { return false; }

    // check data available on a locked port. If port is locked and key is not correct then 
    // 0 is returned
    virtual uint32_t available_locked(uint32_t key) { return 0; }

    // write to a locked port. If port is locked and key is not correct then 0 is returned
    // and write is discarded
    virtual size_t write_locked(const uint8_t *buffer, size_t size, uint32_t key) { return 0; }

    // read from a locked port. If port is locked and key is not correct then 0 is returned
    virtual int16_t read_locked(uint32_t key) { return -1; }
    
    // control optional features
    virtual bool set_options(uint16_t options) { _last_options = options; return options==0; }
    virtual uint16_t get_options(void) const { return _last_options; }

    enum {
        OPTION_RXINV              = (1U<<0),  // invert RX line
        OPTION_TXINV              = (1U<<1),  // invert TX line
        OPTION_HDPLEX             = (1U<<2), // half-duplex (one-wire) mode
        OPTION_SWAP               = (1U<<3), // swap RX and TX pins
        OPTION_PULLDOWN_RX        = (1U<<4), // apply pulldown to RX
        OPTION_PULLUP_RX          = (1U<<5), // apply pullup to RX
        OPTION_PULLDOWN_TX        = (1U<<6), // apply pulldown to TX
        OPTION_PULLUP_TX          = (1U<<7), // apply pullup to TX
        OPTION_NODMA_RX           = (1U<<8), // don't use DMA for RX
        OPTION_NODMA_TX           = (1U<<9), // don't use DMA for TX
        OPTION_MAVLINK_NO_FORWARD = (1U<<10), // don't forward MAVLink data to or from this device
        OPTION_NOFIFO             = (1U<<11), // disable hardware FIFO
        OPTION_NOSTREAMOVERRIDE   = (1U<<12), // don't allow GCS to override streamrates
    };

    enum flow_control {
        FLOW_CONTROL_DISABLE=0, FLOW_CONTROL_ENABLE=1, FLOW_CONTROL_AUTO=2
    };
    virtual void set_flow_control(enum flow_control flow_control_setting) {};
    virtual enum flow_control get_flow_control(void) { return FLOW_CONTROL_DISABLE; }

    virtual void configure_parity(uint8_t v){};
    virtual void set_stop_bits(int n){};

    /* unbuffered writes bypass the ringbuffer and go straight to the
     * file descriptor
     */
    virtual bool set_unbuffered_writes(bool on){ return false; };

    /*
      wait for at least n bytes of incoming data, with timeout in
      milliseconds. Return true if n bytes are available, false if
      timeout
     */
    virtual bool wait_timeout(uint16_t n, uint32_t timeout_ms) { return false; }

    /*
     * Optional method to control the update of the motors. Derived classes
     * can implement it if their HAL layer requires.
     */
    virtual void _timer_tick(void) { }

    /*
      return timestamp estimate in microseconds for when the start of
      a nbytes packet arrived on the uart. This should be treated as a
      time constraint, not an exact time. It is guaranteed that the
      packet did not start being received after this time, but it
      could have been in a system buffer before the returned time.

      This takes account of the baudrate of the link. For transports
      that have no baudrate (such as USB) the time estimate may be
      less accurate.

      A return value of zero means the HAL does not support this API
     */
    virtual uint64_t receive_time_constraint_us(uint16_t nbytes) { return 0; }

    virtual uint32_t bw_in_kilobytes_per_second() const {
        return 57;
    }

    /*
      return true if this UART has DMA enabled on both RX and TX
     */
    virtual bool is_dma_enabled() const { return false; }

#if HAL_UART_STATS_ENABLED
    // request information on uart I/O for this uart, for @SYS/uarts.txt
    virtual void uart_info(ExpandingString &str) {}
#endif

    /*
      software control of the CTS/RTS pins if available. Return false if
      not available
     */
    virtual bool set_RTS_pin(bool high) { return false; };
    virtual bool set_CTS_pin(bool high) { return false; };

    // return true requested baud on USB port
    virtual uint32_t get_usb_baud(void) const { return 0; }

    // disable TX/RX pins for unusued uart
    virtual void disable_rxtx(void) const {}
};