本篇主要介绍RC信号的传输流程。主要包括遥控器信号的接收，解码，发送至FMU，处理，发送至IO，映射至通道。本文以SBUS协议的遥控器为例，其他协议的RC信号除接收与解码步骤外其余均相同。

遥控器信号接收与解码：

遥控器信号接收的代码在 Firmware\src\lib\rc目录下sbus.cpp其中的sbus_input函数中。sbus_input中调用了read(sbus_fd, &buf[0], SBUS_FRAME_SIZE); 函数用来获取SBUS的信号帧，并在结尾调用了sbus_parse 函数对数据帧进行解码将其转化为PWM值。

bool
sbus_input(int sbus_fd, uint16_t *values, uint16_t *num_values, bool *sbus_failsafe, bool *sbus_frame_drop,uint16_t max_channels)
{int        ret = 1;hrt_abstime    now;/** The S.BUS protocol doesn't provide reliable framing,* so we detect frame boundaries by the inter-frame delay.** The minimum frame spacing is 7ms; with 25 bytes at 100000bps* frame transmission time is ~2ms.** We expect to only be called when bytes arrive for processing,* and if an interval of more than 3ms passes between calls,* the first byte we read will be the first byte of a frame.** In the case where byte(s) are dropped from a frame, this also* provides a degree of protection. Of course, it would be better* if we didn't drop bytes...*/now = hrt_absolute_time();/** Fetch bytes, but no more than we would need to complete* a complete frame.*/uint8_t buf[SBUS_FRAME_SIZE * 2];bool sbus_decoded = false;ret = read(sbus_fd, &buf[0], SBUS_FRAME_SIZE);/* if the read failed for any reason, just give up here */if (ret < 1) {return false;}/** Try to decode something with what we got*/if (sbus_parse(now, &buf[0], ret, values, num_values, sbus_failsafe,sbus_frame_drop, &sbus_frame_drops, max_channels)) {sbus_decoded = true;}return sbus_decoded;
}

我们进一步搜索发现sbus_input()函数在px4io.c的controls_tick()函数中被调用了。由此可以定位到px4io.c中。

遥控器信号传递至FMU并处理：

在px4io.c中我们发现这段代码原来是IO芯片中最重要的代码，其主要实现的功能有基础环境的初始化,包括PWM,串口,ADC 等资源的初始化,最后运行一个死循环,用于处理遥控器输入以及与PX4FMU 通信的内容即controls_tick()函数。

int
user_start(int argc, char *argv[])
{/* configure the first 8 PWM outputs (i.e. all of them) */up_pwm_servo_init(0xff);#if defined(CONFIG_HAVE_CXX) && defined(CONFIG_HAVE_CXXINITIALIZE)/* run C++ ctors before we go any further */up_cxxinitialize();# if defined(CONFIG_EXAMPLES_NSH_CXXINITIALIZE)
#       error CONFIG_EXAMPLES_NSH_CXXINITIALIZE Must not be defined! Use CONFIG_HAVE_CXX and CONFIG_HAVE_CXXINITIALIZE.
#   endif#else
#  error platform is dependent on c++ both CONFIG_HAVE_CXX and CONFIG_HAVE_CXXINITIALIZE must be defined.
#endif/* reset all to zero */memset(&system_state, 0, sizeof(system_state));/* configure the high-resolution time/callout interface */hrt_init();/* calculate our fw CRC so FMU can decide if we need to update */calculate_fw_crc();/** Poll at 1ms intervals for received bytes that have not triggered* a DMA event.*/
#ifdef CONFIG_ARCH_DMAhrt_call_every(&serial_dma_call, 1000, 1000, (hrt_callout)stm32_serial_dma_poll, NULL);
#endif/* print some startup info */syslog(LOG_INFO, "\nPX4IO: starting\n");/* default all the LEDs to off while we start */LED_AMBER(false);LED_BLUE(false);LED_SAFETY(false);
#ifdef GPIO_LED4LED_RING(false);
#endif/* turn on servo power (if supported) */
#ifdef POWER_SERVOPOWER_SERVO(true);
#endif/* turn off S.Bus out (if supported) */
#ifdef ENABLE_SBUS_OUTENABLE_SBUS_OUT(false);
#endif/* start the safety switch handler */safety_init();/* initialise the control inputs */controls_init();/* set up the ADC */adc_init();/* start the FMU interface */interface_init();/* add a performance counter for mixing */perf_counter_t mixer_perf = perf_alloc(PC_ELAPSED, "mix");/* add a performance counter for controls */perf_counter_t controls_perf = perf_alloc(PC_ELAPSED, "controls");/* and one for measuring the loop rate */perf_counter_t loop_perf = perf_alloc(PC_INTERVAL, "loop");struct mallinfo minfo = mallinfo();r_page_status[PX4IO_P_STATUS_FREEMEM] = minfo.mxordblk;syslog(LOG_INFO, "MEM: free %u, largest %u\n", minfo.mxordblk, minfo.fordblks);/* initialize PWM limit lib */pwm_limit_init(&pwm_limit);/**    P O L I C E    L I G H T S** Not enough memory, lock down.** We might need to allocate mixers later, and this will* ensure that a developer doing a change will notice* that he just burned the remaining RAM with static* allocations. We don't want him to be able to* get past that point. This needs to be clearly* documented in the dev guide.**/if (minfo.mxordblk < 600) {syslog(LOG_ERR, "ERR: not enough MEM");bool phase = false;while (true) {if (phase) {LED_AMBER(true);LED_BLUE(false);} else {LED_AMBER(false);LED_BLUE(true);}up_udelay(250000);phase = !phase;}}/* Start the failsafe led init */failsafe_led_init();/** Run everything in a tight loop.*/uint64_t last_debug_time = 0;uint64_t last_heartbeat_time = 0;uint64_t last_loop_time = 0;for (;;) {dt = (hrt_absolute_time() - last_loop_time) / 1000000.0f;last_loop_time = hrt_absolute_time();if (dt < 0.0001f) {dt = 0.0001f;} else if (dt > 0.02f) {dt = 0.02f;}/* track the rate at which the loop is running */perf_count(loop_perf);/* kick the mixer */perf_begin(mixer_perf);mixer_tick();perf_end(mixer_perf);/* kick the control inputs */perf_begin(controls_perf);controls_tick();perf_end(controls_perf);/* some boards such as Pixhawk 2.1 madethe unfortunate choice to combine the blue led channel withthe IMU heater. We need a software hack to fix the hardware hackby allowing to disable the LED / heater.*/if (r_page_setup[PX4IO_P_SETUP_THERMAL] == PX4IO_THERMAL_IGNORE) {/*blink blue LED at 4Hz in normal operation. When inoverride blink 4x faster so the user can clearly seethat override is happening. This helps whenpre-flight testing the override system*/uint32_t heartbeat_period_us = 250 * 1000UL;if (r_status_flags & PX4IO_P_STATUS_FLAGS_OVERRIDE) {heartbeat_period_us /= 4;}if ((hrt_absolute_time() - last_heartbeat_time) > heartbeat_period_us) {last_heartbeat_time = hrt_absolute_time();heartbeat_blink();}} else if (r_page_setup[PX4IO_P_SETUP_THERMAL] < PX4IO_THERMAL_FULL) {/* switch resistive heater off */LED_BLUE(false);} else {/* switch resistive heater hard on */LED_BLUE(true);}update_mem_usage();ring_blink();check_reboot();/* check for debug activity (default: none) */show_debug_messages();/* post debug state at ~1Hz - this is via an auxiliary serial port* DEFAULTS TO OFF!*/if (hrt_absolute_time() - last_debug_time > (1000 * 1000)) {isr_debug(1, "d:%u s=0x%x a=0x%x f=0x%x m=%u",(unsigned)r_page_setup[PX4IO_P_SETUP_SET_DEBUG],(unsigned)r_status_flags,(unsigned)r_setup_arming,(unsigned)r_setup_features,(unsigned)mallinfo().mxordblk);last_debug_time = hrt_absolute_time();}}
}

在pixhawk中IO芯片与fmu芯片是利用高速串口进行通讯。在px4io.c中这段代码中找到了一个中断初始化函数interface_init(); 在中断初始化函数中找到了中断服务函数，serial_interrupt()；这个中断服务函数便是fmu与io通讯的地方。进入中断服务函数我们发现IO侧向fmu侧发送数据属于被动发送，只有接收到fmu向io发送的数据，io才会向fmu返回数据。

static int
serial_interrupt(int irq, void *context, FAR void *arg)
{static bool abort_on_idle = false;uint32_t sr = rSR; /* get UART status register */(void)rDR;        /* required to clear any of the interrupt status that brought us here */if (sr & (USART_SR_ORE |    /* overrun error - packet was too big for DMA or DMA was too slow */USART_SR_NE |       /* noise error - we have lost a byte due to noise */USART_SR_FE)) {     /* framing error - start/stop bit lost or line break */perf_count(pc_errors);if (sr & USART_SR_ORE) {perf_count(pc_ore);}if (sr & USART_SR_NE) {perf_count(pc_ne);}if (sr & USART_SR_FE) {perf_count(pc_fe);}/* send a line break - this will abort transmission/reception on the other end */rCR1 |= USART_CR1_SBK;/* when the line goes idle, abort rather than look at the packet */abort_on_idle = true;}if (sr & USART_SR_IDLE) {/** If we saw an error, don't bother looking at the packet - it should have* been aborted by the sender and will definitely be bad. Get the DMA reconfigured* ready for their retry.*/if (abort_on_idle) {abort_on_idle = false;dma_reset();return 0;}/** The sender has stopped sending - this is probably the end of a packet.* Check the received length against the length in the header to see if* we have something that looks like a packet.*/unsigned length = sizeof(dma_packet) - stm32_dmaresidual(rx_dma);if ((length < 1) || (length < PKT_SIZE(dma_packet))) {/* it was too short - possibly truncated */perf_count(pc_badidle);dma_reset();return 0;}/** Looks like we received a packet. Stop the DMA and go process the* packet.*/perf_count(pc_idle);stm32_dmastop(rx_dma);rx_dma_callback(rx_dma, DMA_STATUS_TCIF, NULL);}return 0;
}

serial_interrupt()接收数据、清除中断后，再调用rx_dma_callback()进行DMA数据的处理和发送IO侧的数据至fmu。

static void
rx_dma_callback(DMA_HANDLE handle, uint8_t status, void *arg)
{/** We are here because DMA completed, or UART reception stopped and* we think we have a packet in the buffer.*/perf_begin(pc_txns);/* disable UART DMA */rCR3 &= ~(USART_CR3_DMAT | USART_CR3_DMAR);/* handle the received packet */rx_handle_packet();/* re-set DMA for reception first, so we are ready to receive before we start sending */dma_reset();/* send the reply to the just-processed request */dma_packet.crc = 0;dma_packet.crc = crc_packet(&dma_packet);stm32_dmasetup(tx_dma,(uint32_t)&rDR,(uint32_t)&dma_packet,PKT_SIZE(dma_packet),DMA_CCR_DIR       |DMA_CCR_MINC       |DMA_CCR_PSIZE_8BITS    |DMA_CCR_MSIZE_8BITS);stm32_dmastart(tx_dma, NULL, NULL, false); //发送io侧数据至fmurCR3 |= USART_CR3_DMAT;perf_end(pc_txns);
}

在fmu侧px4io.cpp文件中io_get_raw_rc_input()函数完成了遥控信号的获取并将其通过orb广播出去，fmu的其他文件便可通过orb对数据进行处理。

发送处理后的数据至IO并将其映射至通道中：

其他文件将rc信号处理完成后通过ORB ORB_ID(actuator_controls_0) 广播之， px4io.cpp通过io_set_control_state()函数将广播的数据进行订阅复制，并通过不断调用最终在px4io.cpp的task_main函数中将其送回fmu中。IO测的中断处理函数接收到数据后将其解码为PWM值,然后调用mixer_tick();函数对其进行通道映射输出真正的PWM值。

本文大部分均为博主原创且讲的相对比较浅显，更详细深层次的内容请参考下面的博客。本人才识浅薄，并且刚接触pixhawk不久，大部分为博主自己推测和百度的结果，有错误之处还请指出，博主将进行更正。谢谢

参考文章：

https://blog.csdn.net/SIR_wkp/article/details/80548262

https://blog.csdn.net/czyv587/article/details/51445308

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pixhawk RC信号传输流程代码版本pixhawk1.5.5

遥控器信号接收与解码：

遥控器信号传递至FMU并处理：

发送处理后的数据至IO并将其映射至通道中：

pixhawk RC信号传输流程代码版本pixhawk1.5.5相关推荐

最新文章

热门文章

pixhawk RC信号传输流程 代码版本pixhawk1.5.5

遥控器信号接收与解码：

遥控器信号传递至FMU并处理：

发送处理后的数据至IO并将其映射至通道中：

pixhawk RC信号传输流程 代码版本pixhawk1.5.5相关推荐

最新文章

热门文章

pixhawk RC信号传输流程代码版本pixhawk1.5.5

pixhawk RC信号传输流程代码版本pixhawk1.5.5相关推荐