If you like my project vote for "A Smarter Tricopter - Yuri Tikhonov"


Good day comrades!

As I promised, today we talk about the communication of PSoC 4 with standard MultiWii PC Software. Today the following modules are 90% ready:

  1. UpTime system.
  2. System of communication with the receiver (this week I'll fix some bugs).
  3. UART module for configuration and telemetry.


"PSoC schematics" looks like this:



The testing station has not changed and it has the view as follows:



Expectedly, I want to talk about the UART module.

Green: UART communication module works using interrupts. I use two interrupts in a single handler (UART_INTR_TX_EMPTY and UART_INTR_RX_NOT_EMPTY).

Now I only modify MultiWii to work correctly with the PSoC, later I'll make it's optimization.


CY_ISR(serialInterruptHandler) // interrupt
    if ( (UART_GetTxInterruptMode() & UART_INTR_TX_EMPTY) != 0 ) // RX interrupt
        UART_ClearTxInterruptSource(UART_INTR_TX_EMPTY); // clear interrupt
        if( headTX != tailTX )
            UART_UartPutChar(bufTX[tailTX++]); // Transmit next byte in the ring
        if ( tailTX == headTX )                // Check if all data is transmitted
            serialIntOff;                      // Disable transmitter interrupt

    if ( (UART_GetRxInterruptMode() & UART_INTR_RX_NOT_EMPTY) != 0 ) // RX interrupt
        UART_ClearRxInterruptSource(UART_INTR_RX_NOT_EMPTY);  // clear interrupt
        if ( UART_SpiUartGetRxBufferSize() < 1) return;
        uint8_t d = UART_UartGetChar();
        uint8_t i = serialHeadRX[0] + 1;
        if (i != serialTailRX[0])
            serialBufferRX[serialHeadRX[0]][0] = d;
            serialHeadRX[0] = i;


To better understand how the code works, here are some explanations:

  • as buffers Rx/Tx we use bufTX[] and serialBufferRX[][0] arrays;
  • tail and head of this buffers are stored, respectively, in tailTX, serialHeadRX[0], headTX and serialTailRX[0];
  • serialIntOff = UART_SetTxInterruptMode(0x00 - disable Tx interrupts);
  • serialIntOn = UART_SetTxInterruptMode(UART_INTR_TX_EMPTY) - turn on Tx interrupts (all data was transmitted and hardware Tx buffer is empty);
  • UART_INTR_RX_NOT_EMPTY - this interrupt occurs if the input UART read some data.


I would also speak about other functions adapted for the correct work with MultiWii GUI:


1. Adding two byte word in the Tx buffer (unsigned int16):

void serialize16(int16_t a)
  bufTX[headTX++]  = a;
  bufTX[headTX++]  = a>>8&0xff;


2. Adding one byte word in the Tx buffer (unsigned int8):

void serialize8(uint8_t a)
  bufTX[headTX++]  = a;


3. Turn on UART transmitting (realy - turn on Tx interrupts):

void UartSendData(void)
{                      // Data transmission acivated when the ring is not empty
  serialIntOn;          // Enable transmitter interrupt



4. Activate the data transmission on the UART. In my project I use only one module UART, and only one fixed speed 115200 baud, so variables port and baud temporarily left only for compatibility with MultiWii:

void SerialOpen(uint8_t port, uint32_t baud)


5. Turn off UART transmitting (variable port is only for  compatibility with MultiWii):

void SerialEnd(uint8_t port)


6. Reading data via UART. Realy - buffer reading (variable port is only for compatibility with MultiWii):

uint8_t SerialRead(uint8_t port)
    uint8_t c = serialBufferRX[serialTailRX[port]][port];
    if ((serialHeadRX[port] != serialTailRX[port])) serialTailRX[port] = serialTailRX[port] + 1;
    return c;


7. Checking Rx data availability (variable port is only for compatibility with MultiWii):

uint8_t SerialAvailable(uint8_t port)
  return serialHeadRX[port] - serialTailRX[port];


8. Transfer one byte via UART (variable port is only for compatibility with MultiWii):

void SerialWrite(uint8_t port,uint8_t c)
  UartSendData(); // Serial TX is driven via a buffer and a background intterupt


The function of ensuring communication with MultiWii GUI has a name serialCom(), It is currently undergoing a "permanent modifications," because yet I have not IMU, EEPROM, and some other functions.


So, the moment of truth, start of MultiWii GUI:



As you can see, telemetry data is successfully transferred! Reaction to the sticks of radio equipment, fast and accurate, in general I am happy!

Next week I plan to do another small but necessary system: EEPROM. Because without it, store settings and calibration unit is not yet possible.

See you next week!



1PSoC 4 Tricopter Part #1Introduction
2PSoC 4 Tricopter Part #2Purchase of components from Farnell and HobbyKing
3PSoC 4 Tricopter Part #3PSoC firmware: upTime & Rx
4PSoC 4 Tricopter Part #4PSoC firmware: UART & MultiWii GUI
5PSoC 4 Tricopter Part #5PSoC firmware: EEPROM emulation
6PSoC 4 Tricopter Part #6PSoC firmware: Servo & ESC control
7PSoC 4 Tricopter Part #7PSoC firmware: IMU, LED's & PID
8PSoC 4 Tricopter Part #8Hardware: PCB
9PSoC 4 Tricopter Part #9Hardware: tricopter's frame
10PSoC 4 Tricopter Part #10Hardware: YAW mechanics & motors
11PSoC 4 Tricopter Part #11Hardware: ESC's, wires & misc
12PSoC 4 Tricopter Part #12Final: The first fly


If you like my project vote for "A Smarter Tricopter - Yuri Tikhonov"