ibus is a Flysky RC receiver protocol

KEYWORD - i-bus, FLYSKY, UART, STM32 HAL DMA

• Receive stick data using DMA mode
  • 1000 - 2000
• Software fail-safe

• STM32CubeIDE
• STM32 HAL driver
• STM32F411
• FLYSKY Transmitter & Receiver
  • FS-i6, FS-A8S (fail-safe X)

• The ibus protocol is one of RX protocols developed by Flysky
• half-duplex
• Control multiple servos and motors using a single digital line.
• Support 14 channels
• New value can be read every 7ms
• The values received for each channel are between 1000 and 2000
• The ibus library requires a dedicated hardware serial (UART) port on microcontroller
  • UART RX required
  • 115200 baud
  • 8N1
• Data frame
  • 32 bytes
  • Structure
    • Example set of 32 bytes

      20 40 DB 5 DC 5 54 5 DC 5 E8 3 D0 7 D2 5 E8 3 DC 5 DC 5 DC 5 DC 5 DC 5 DC 5 DA F3
      

    • Section

      Protocol length	Command code	CH1	CH2	CH3	...	CH14	Checksum
      0x20	0x40	0xDB 0x05	0xDC 0x05	0x54 0x05	...	0xDC 0x05	0xDA 0xF3

  • Little Endian

    ibus data	HEX	DEC
    CH1	0x05DB	1499
    CH2	0x05DC	1500
    CH3	0x0554	1364
    ...	...	...
    CH14	0x05DC	1500
    Checksum	0xF3DA

  • Checksum calculation
    • 0xFFFF - (sum of previous 30 bytes)

• UART
• DMA

• UART1, 6 Channels

/* User configuration */
#define IBUS_UART				(&huart1)
#define IBUS_USER_CHANNELS		6		// Use 6 channels

• Only contain ibus things

#include "ibus.h"

// variables to store ibus data
uint16_t ibus_data[IBUS_USER_CHANNELS];

// for software fail-safe
void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart);

int main(void)
{
    ibus_init();

    while(1)
    {
        ibus_read(ibus_data);
	    ibus_soft_failsafe(ibus_data, 10); // if ibus is not updated, clear ibus data.
	    HAL_Delay(10);
    }
}

void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart)
{
	if(huart == IBUS_UART)
		ibus_reset_failsafe();
}