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MicroBitSerial.cpp if(newHead != rxBuffTail) This may result in loss of received data. #460

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zfm076 opened this issue Mar 11, 2020 · 7 comments
Open

MicroBitSerial.cpp if(newHead != rxBuffTail) This may result in loss of received data. #460

zfm076 opened this issue Mar 11, 2020 · 7 comments

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@zfm076
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zfm076 commented Mar 11, 2020 •
edited
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void MicroBitSerial::dataReceived()
{
    //get the received character
    //Note: always read from the serial to clear the RX interrupt
    char c = getc();

    if(!(status & MICROBIT_SERIAL_RX_BUFF_INIT))
        return;

    int delimeterOffset = 0;
    int delimLength = this->delimeters.length();

    //iterate through our delimeters (if any) to see if there is a match
    while(delimeterOffset < delimLength)
    {
        //fire an event if there is to block any waiting fibers
        if(this->delimeters.charAt(delimeterOffset) == c)
            MicroBitEvent(MICROBIT_ID_SERIAL, MICROBIT_SERIAL_EVT_DELIM_MATCH);

        delimeterOffset++;
    }

    uint16_t newHead = (rxBuffHead + 1) % rxBuffSize;

    //look ahead to our newHead value to see if we are about to collide with the tail
    if(newHead != rxBuffTail)
    {
        //if we are not, store the character, and update our actual head.
        this->rxBuff[rxBuffHead] = c;
        rxBuffHead = newHead;

        //if we have any fibers waiting for a specific number of characters, unblock them
        if(rxBuffHeadMatch >= 0)
            if(rxBuffHead == rxBuffHeadMatch)
            {
                rxBuffHeadMatch = -1;
                MicroBitEvent(MICROBIT_ID_SERIAL, MICROBIT_SERIAL_EVT_HEAD_MATCH);
            }
    }
    else
        //otherwise, our buffer is full, send an event to the user...
        MicroBitEvent(MICROBIT_ID_SERIAL, MICROBIT_SERIAL_EVT_RX_FULL);
}

I found a problem during the serial communication test: My computer sends data continuously through the serial port ( baud(57600) ) and no delay. and then my microbit just do one thing:The data is read and sent to the computer:

        while(uBit.serial.isReadable())
        {
            data = uBit.serial.read(ASYNC);
            uBit.serial.send( &data ,1, ASYNC);
            uBit.sleep(0.05); //I deliberately increase the delay to let the serial port receive queue fill up, 
                                         in order to see what happens
        }

Then,I found that a lot of the data sent to the computer had been lost. I see the source inside this sentence : if(newHead != rxBuffTail). that will cause my data to be lost. After I mask this code (if(newHead != rxBuffTail)), the data will still be lost, but much less.Is there any way to ensure the integrity of my data?Even if it overwrites the original data.
@martinwork
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Related? #441

@zfm076
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zfm076 commented Mar 12, 2020 •
edited
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Related? #441

This problem occurs when the queue is full.My computer has been sending this sentence(0xFF 0x01 0x02 0x03 0x04 0x05 0x06 0xAA) very quickly.Then microbit prints the received data as follows:
FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 02 FF 01 FF 01 02 FF 01 02 FF 01 FF 01 02 FF 01 03 FF 01 FF 01 FF 01 02 05 FF 03 FF 01 FF 01 02 FF 01 FF 01 02 06 FF FF 01 02 FF 01 02 FF 01 FF 01 02 FF 01 02 FF 01 05 FF 01 AA FF 01 FF 01 03 FF 02 FF 01 FF 01 02 FF 01 FF 01 02 FF 01 02 FF 01 FF 01 02 FF 01 FF 01 02 05 FF 01 02 FF 01 FF 01 FF 01 FF 01 02 FF 01 02 03 FF 01 FF 01 02 FF FF 01 02 05 FF 01 FF 01 FF 01 02 FF 01 02 FF 01 05 FF 01 FF 01 FF 01 02 FF 01 AA FF 01 02 FF 01 FF 01 AA FF 01 FF 01 02 FF 01 06 FF 01 FF 01 AA FF 01 05 FF 01 FF 01 03 FF 01 FF 01 06 FF 01 FF 01 02 FF 01 05 FF 01 FF 01 02 FF 01 FF 01 FF 01 02 03 FF 01 FF 01 04 FF 01 FF 01 06 FF 01 FF 01 02 06 FF 04 FF 01 FF 01 02 FF 01 02 FF 01 FF 01 FF 01 02 05 FF 01 FF 01 05 FF 01 FF 01 05 FF 01 FF 01 AA FF 01 FF 01 02 AA FF 01 FF 01 FF 01 02 FF 01 AA FF 01 02 FF 04 FF 01 FF 01 FF 01 02 AA FF 01 02 FF AA FF 01 FF 01 FF 01 02 06 FF 01 FF 01 05 FF 01 FF 01 02 FF 01 FF 01 02 FF 01 02 FF 01 02 FF 02 FF 01 02 FF 02 FF 01 AA FF 02 FF 01 02 FF 01 02 FF 01 FF 01 05 FF 01 FF 01 02 FF 01 06 FF 01 FF 01 02 FF 01 FF 01 02 FF 01 FF 01 02 FF 01 AA FF 01 FF 01 AA FF 01 02 FF 01 FF 01 03 FF 01 FF 01 04 FF 01 FF 01 02 06 FF 01 FF 01 02 FF 05 FF
You can see that the data is normal when the queue is not full.When the queue is full, the Data frame is cut off.I know the data will be lost, But data frames should not be cut off in large Numbers.

And then I did some code masking (in void MicroBitSerial::dataReceived() function ):

    //look ahead to our newHead value to see if we are about to collide with the tail
    //if(newHead != rxBuffTail) //Shielding here!!!!!!!!!!!!!!!!!!!!!<<<<<<<<<<<<<
    {
        //if we are not, store the character, and update our actual head.
        this->rxBuff[rxBuffHead] = c;
        rxBuffHead = newHead;

        //if we have any fibers waiting for a specific number of characters, unblock them
        if(rxBuffHeadMatch >= 0)
            if(rxBuffHead == rxBuffHeadMatch)
            {
                rxBuffHeadMatch = -1;
                MicroBitEvent(MICROBIT_ID_SERIAL, MICROBIT_SERIAL_EVT_HEAD_MATCH);
            }
    }
    //else   //Shielding here!!!!!!!!!!!!!!!!!!!!!<<<<<<<<<<<<<
        //otherwise, our buffer is full, send an event to the user...
       // MicroBitEvent(MICROBIT_ID_SERIAL, MICROBIT_SERIAL_EVT_RX_FULL); //Shielding here!!!!!!!!!!!!!!!!!!!!!<<<<<<<<<<<<<

Then the computer sends the same data(0xFF 0x01 0x02 0x03 0x04 0x05 0x06 0xAA),Then microbit prints the received data as follows:
FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA FF 01 02 03 04 05 06 AA

You can see that when the queue is full you lose data, but many frames of data are not cut off.The queue is full but the data is relatively complete. So Does this code( if(newHead != rxBuffTail) )in void MicroBitSerial::dataReceived() function cause the data to be cut off?

@martinwork
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When the buffer is full, incoming bytes are dropped. When read() removes one byte, the next incoming byte will be added.

By commenting out the buffer full check, incoming bytes are overwriting old data. Data is still being lost. Reading will potentially get recent bytes followed by older ones.

Try sending frames with a counter, then see how the data looks:
0xFF 0x01 0x02 0x03 0x04 0x05 0x06 0xAA,
0xFF 0x02 0x02 0x03 0x04 0x05 0x06 0xAA,
0xFF 0x03 0x02 0x03 0x04 0x05 0x06 0xAA,
etc.

Serial works one byte at a time. Maybe set the buffer size to be a multiple of 8, check the size of the data available and read in multiples of 8.

@zfm076
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zfm076 commented Mar 13, 2020 •
edited
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When the buffer is full, incoming bytes are dropped. When read() removes one byte, the next incoming byte will be added.

By commenting out the buffer full check, incoming bytes are overwriting old data. Data is still being lost. Reading will potentially get recent bytes followed by older ones.

Try sending frames with a counter, then see how the data looks:
0xFF 0x01 0x02 0x03 0x04 0x05 0x06 0xAA,
0xFF 0x02 0x02 0x03 0x04 0x05 0x06 0xAA,
0xFF 0x03 0x02 0x03 0x04 0x05 0x06 0xAA,
etc.

Serial works one byte at a time. Maybe set the buffer size to be a multiple of 8, check the size of the data available and read in multiples of 8.

My microbit code:

#include "MicroBit.h"
MicroBit uBit;
int main()
{
    uBit.init();
    uBit.serial.baud(57600);
    uBit.serial.setRxBufferSize(200);
    uBit.serial.setTxBufferSize(200);
   
    while(1)
   {
        while(uBit.serial.isReadable())
        {
            uBit.serial.read( &data ,1, ASYNC);
            uBit.serial.send( &data ,1, ASYNC);
            uBit.sleep(0.05);//I deliberately increase the delay to let the serial port receive queue fill up, 
                                         in order to see what happens
        }
    }
    release_fiber();
}

I take your advice,sending frames with a counter,My computer sent 255 frames of data,Then microbit prints the received data as follows:
AA 01 02 03 04 05 06 FF AA 02 02 03 04 05 06 FF AA 03 02 03 04 05 06 FF AA 04 02 03 04 05 06 FF AA 05 02 03 04 05 06 FF AA 06 02 03 04 05 06 FF AA 07 02 03 04 05 06 FF AA 08 02 03 04 05 06 FF AA 09 02 03 04 05 06 FF AA 0A 02 03 04 05 06 FF AA 0B 02 03 04 05 06 FF AA 0C 02 03 04 05 06 FF AA 0D 02 03 04 05 06 FF AA 0E 02 03 04 05 06 FF AA 0F 02 03 04 05 06 FF AA 10 02 03 04 05 06 FF AA 11 02 03 04 05 06 FF AA 12 02 03 04 05 06 FF AA 13 02 03 04 05 06 FF AA 14 02 03 04 05 06 FF AA 15 02 03 04 05 06 FF AA 16 02 03 04 05 06 FF AA 17 02 03 04 05 06 FF AA 18 02 03 04 05 06 FF AA 19 02 03 04 05 06 FF AA 1A 02 03 04 05 06 FF AA 1B 02 03 04 05 06 FF AA 1C 02 03 04 05 06 FF AA 1D 02 03 04 05 06 FF AA 1E 02 03 04 05 06 FF AA 1F 02 03 04 05 06 FF AA 20 02 03 04 05 06 FF AA 21 02 03 04 05 06 FF AA 22 02 03 04 05 06 FF AA 23 02 03 04 05 06 FF AA 24 02 03 04 05 06 FF AA 25 02 03 04 05 06 FF AA 26 02 03 04 05 06 FF AA 27 02 03 04 05 06 FF AA 28 02 03 04 05 06 FF AA 29 02 03 04 05 06 FF AA 2A 02 03 04 05 06 FF AA 2B 02 03 04 05 06 FF AA 2C 02 03 04 05 06 FF AA 2D 02 03 04 05 06 FF AA 2E 02 03 04 05 06 FF AA 2F 02 03 04 05 06 FF AA 30 02 03 04 05 06 FF AA 31 02 03 04 05 06 FF AA 32 02 03 04 05 06 FF AA 33 02 03 04 05 06 FF AA 34 02 03 04 05 06 FF AA 35 02 03 04 05 06 FF AA 36 02 03 04 05 06 FF AA 37 02 03 04 05 06 FF AA 38 02 03 04 05 06 FF AA 39 02 03 04 05 06 FF AA 3A 02 03 04 05 06 FF AA 3B 02 03 04 05 06 FF AA 3C 02 03 04 05 06 FF AA 3D 02 03 04 05 06 FF AA 3E 02 03 04 05 06 FF AA 3F 02 03 04 05 06 FF AA 40 02 03 04 05 06 FF AA 41 02 03 04 05 06 FF AA 42 02 03 04 05 AA 43 02 03 04 AA 44 02 03 04 AA 45 02 03 04 AA 46 02 03 04 AA 47 02 03 04 AA 48 02 03 04 AA 49 02 03 04 AA 4A 02 03 04 AA 4B 02 03 04 AA 4C 02 03 04 AA 4D 02 03 04 AA 4E 02 03 04 AA 4F 02 03 04 AA 50 02 03 04 AA 51 02 03 04 AA 52 02 03 04 AA 53 02 03 04 AA 54 02 03 04 AA 55 02 03 04 AA 56 02 03 04 AA 57 02 03 04 AA 58 02 03 04 AA 59 02 03 04 AA 5A 02 03 04 AA 5B 02 03 04 AA 5C 02 03 04 AA 5D 02 03 04 AA 5E 02 03 04 AA 5F 02 03 04 AA 60 02 03 04 AA 61 02 03 04 AA 62 02 03 04 AA 63 02 03 04 AA 64 02 03 04 AA 65 02 03 04 AA 66 02 03 04 AA 67 02 03 04 AA 68 02 03 04 AA 69 02 03 04 AA 6A 02 03 04 AA 6B 02 03 04 AA 6C 02 03 04 AA 6D 02 03 04 AA 6E 02 03 04 AA 6F 02 03 04 AA 70 02 03 04 AA 71 02 03 04 AA 72 02 03 04 AA 73 02 03 04 AA 74 02 03 04 AA 75 02 03 04 AA 76 02 03 04 AA 77 02 03 04 AA 78 02 03 04 AA 79 02 03 04 AA 7A 02 03 04 AA 7B 02 03 04 AA 7C 02 03 04 AA 7D 02 03 04 AA 7E 02 03 04 AA 7F 02 03 04 AA 80 02 03 04 AA 81 02 03 04 AA 82 02 03 04 AA 83 02 03 04 AA 84 02 03 04 AA 85 02 03 04 AA 86 02 03 04 AA 87 02 03 04 AA 88 02 03 04 AA 89 02 03 04 AA 8A 02 03 04 AA 8B 02 03 04 AA 8C 02 03 04 AA 8D 02 03 04 AA 8E 02 03 04 AA 8F 02 03 04 AA 90 02 03 04 AA 91 02 03 04 AA 92 02 03 04 AA 93 02 03 04 AA 94 02 03 04 AA 95 02 03 04 AA 96 02 03 04 AA 97 02 03 04 AA 98 02 03 04 AA 99 02 03 04 AA 9A 02 03 04 AA 9B 02 03 04 AA 9C 02 03 04 AA 9D 02 03 04 AA 9E 02 03 04 AA 9F 02 03 04 AA A0 02 03 04 AA A1 02 03 04 AA A2 02 03 04 AA A3 02 03 04 AA A4 02 03 04 AA A5 02 03 04 AA A6 02 03 04 AA A7 02 03 04 AA A8 02 03 04 AA A9 02 03 04 AA AA 02 03 04 AA AB 02 03 04 AA AC 02 03 04 AA AD 02 03 04 AA AE 02 03 04 AA AF 02 03 04 AA B0 02 03 04 AA B1 02 03 04 AA B2 02 03 04 AA B3 02 03 04 AA B4 02 03 04 AA B5 02 03 04 AA B6 02 03 04 AA B7 02 03 04 AA B8 02 03 04 AA B9 02 03 04 AA BA 02 03 04 AA BB 02 03 04 AA BC 02 03 04 AA BD 02 03 04 AA BE 02 03 04 AA BF 02 03 04 AA C0 02 03 04 AA C1 02 03 04 AA C2 02 03 04 AA C3 02 03 04 AA C4 02 03 04 AA C5 02 03 04 AA C6 02 03 04 AA C7 02 03 04 AA C8 02 03 04 AA C9 02 03 04 AA CA 02 03 04 AA CB 02 03 04 AA CC 02 03 04 AA CD 02 03 04 AA CE 02 03 04 AA CF 02 03 04 AA D0 02 03 04 AA D1 02 03 04 AA D2 02 03 04 AA D3 02 03 04 AA D4 02 03 04 AA D5 02 03 04 AA D6 02 03 04 AA D7 02 03 04 AA D8 02 03 04 AA D9 02 03 04 AA DA 02 03 04 AA DB 02 03 04 AA DC 02 03 04 AA DD 02 03 04 AA DE 02 03 04 AA DF 02 03 04 AA E0 02 03 04 AA E1 02 03 04 AA E2 02 03 04 AA E3 02 03 04 AA E4 02 03 04 AA E5 02 03 04 AA E6 02 03 04 AA E7 02 03 04 AA E8 02 03 04 AA E9 02 03 04 AA EA 02 03 04 AA EB 02 03 04 AA EC 02 03 04 AA ED 02 03 04 AA EE 02 03 04 AA EF 02 03 04 AA F0 02 03 04 AA F1 02 03 04 AA F2 02 03 04 AA F3 02 03 04 AA F4 02 03 04 AA F5 02 03 04 AA F6 02 03 04 AA F7 02 03 04 AA F8 02 03 04 AA F9 02 03 04 AA FA 02 03 04 AA FB 02 03 04 AA FC 02 03 04 AA FD 02 03 04 AA FE 02 03 04 AA FF 02 03 04

Then By commenting out the buffer full check,The microbit prints the received data as follows:
AA 01 02 03 04 05 06 FF AA 02 02 03 04 05 06 FF AA 03 02 03 04 05 06 FF AA 04 02 03 04 05 06 FF AA 05 02 03 04 05 06 FF AA 06 02 03 04 05 06 FF AA 07 02 03 04 05 06 FF AA 08 02 03 04 05 06 FF AA 09 02 03 04 05 06 FF AA 0A 02 03 04 05 06 FF AA 0B 02 03 04 05 06 FF AA 0C 02 03 04 05 06 FF AA 0D 02 03 04 05 06 FF AA 0E 02 03 04 05 06 FF AA 0F 02 03 04 05 06 FF AA 10 02 03 04 05 06 FF AA 11 02 03 04 05 06 FF AA 12 02 03 04 05 06 FF AA 13 02 03 04 05 06 FF AA 14 02 03 04 05 06 FF AA 15 02 03 04 05 06 FF AA 16 02 03 04 05 06 FF AA 17 02 03 04 05 06 FF AA 18 02 03 04 05 06 FF AA 19 02 03 04 05 06 FF AA 1A 02 03 04 05 06 FF AA 1B 02 03 04 05 06 FF AA 1C 02 03 04 05 06 FF AA 1D 02 03 04 05 06 FF AA 1E 02 03 04 05 06 FF AA 1F 02 03 04 05 06 FF AA 20 02 03 04 05 06 FF AA 21 02 03 04 05 06 FF AA 22 02 03 04 05 06 FF AA 23 02 03 04 05 06 FF AA 24 02 03 04 05 06 FF AA 25 02 03 04 05 06 FF AA 26 02 03 04 05 06 FF AA 27 02 03 04 05 06 FF AA 28 02 03 04 05 06 FF AA 29 02 03 04 05 FF AA 43 02 03 04 05 06 FF AA 44 02 03 04 05 06 FF AA 45 02 03 04 05 06 FF AA 46 02 03 04 05 06 FF AA 47 02 03 04 05 06 FF AA 48 02 03 04 05 06 FF AA 49 02 03 04 05 06 FF AA 4A 02 03 04 05 06 FF AA 4B 02 03 04 05 06 FF AA 4C 02 03 04 05 06 FF AA 4D 02 03 04 05 06 FF AA 4E 02 03 04 05 06 FF AA 4F 02 03 04 05 06 FF AA 50 02 03 04 05 06 FF AA 51 02 03 04 05 06 FF AA 52 02 03 04 05 06 FF AA 53 02 03 04 05 06 FF AA 54 02 03 04 05 06 FF AA 55 02 03 04 05 06 FF AA 56 02 03 04 05 06 FF AA 57 02 03 04 05 06 FF AA 58 02 03 04 05 06 FF AA 59 02 03 04 05 06 FF AA 5A 02 03 04 05 06 FF AA 5B 02 03 04 05 06 FF AA 5C 02 03 04 05 06 FF AA 5D 02 03 04 05 06 FF AA 5E 02 03 04 05 06 FF AA 5F 02 03 04 05 06 FF AA 60 02 03 04 05 06 FF AA 61 02 03 04 05 06 FF AA 62 02 03 04 05 06 FF AA 63 02 03 04 05 06 FF AA 64 02 03 04 05 06 FF AA 65 02 03 04 05 06 FF AA 66 02 03 04 05 06 FF AA 67 02 03 04 05 06 FF AA 68 02 03 04 05 06 FF AA 69 02 03 04 05 06 FF AA 6A 02 03 04 05 06 FF AA 6B 02 03 04 05 FF AA 85 02 03 04 05 06 FF AA 86 02 03 04 05 06 FF AA 87 02 03 04 05 06 FF AA 88 02 03 04 05 06 FF AA 89 02 03 04 05 06 FF AA 8A 02 03 04 05 06 FF AA 8B 02 03 04 05 06 FF AA 8C 02 03 04 05 06 FF AA 8D 02 03 04 05 06 FF AA 8E 02 03 04 05 06 FF AA 8F 02 03 04 05 06 FF AA 90 02 03 04 05 06 FF AA 91 02 03 04 05 06 FF AA 92 02 03 04 05 06 FF AA 93 02 03 04 05 06 FF AA 94 02 03 04 05 06 FF AA 95 02 03 04 05 06 FF AA 96 02 03 04 05 06 FF AA 97 02 03 04 05 06 FF AA 98 02 03 04 05 06 FF AA 99 02 03 04 05 06 FF AA 9A 02 03 04 05 06 FF AA 9B 02 03 04 05 06 FF AA 9C 02 03 04 05 06 FF AA 9D 02 03 04 05 06 FF AA 9E 02 03 04 05 06 FF AA 9F 02 03 04 05 06 FF AA A0 02 03 04 05 06 FF AA A1 02 03 04 05 06 FF AA A2 02 03 04 05 06 FF AA A3 02 03 04 05 06 FF AA A4 02 03 04 05 06 FF AA A5 02 03 04 05 06 FF AA A6 02 03 04 05 06 FF AA A7 02 03 04 05 06 FF AA A8 02 03 04 05 06 FF AA A9 02 03 04 05 06 FF AA AA 02 03 04 05 06 FF AA AB 02 03 04 05 06 FF AA AC 02 03 04 05 06 FF AA AD 02 03 04 05 FF AA C7 02 03 04 05 06 FF AA C8 02 03 04 05 06 FF AA C9 02 03 04 05 06 FF AA CA 02 03 04 05 06 FF AA CB 02 03 04 05 06 FF AA CC 02 03 04 05 06 FF AA CD 02 03 04 05 06 FF AA CE 02 03 04 05 06 FF AA CF 02 03 04 05 06 FF AA D0 02 03 04 05 06 FF AA D1 02 03 04 05 06 FF AA D2 02 03 04 05 06 FF AA D3 02 03 04 05 06 FF AA D4 02 03 04 05 06 FF AA D5 02 03 04 05 06 FF AA D6 02 03 04 05 06 FF AA D7 02 03 04 05 06 FF AA D8 02 03 04 05 06 FF AA D9 02 03 04 05 06 FF AA DA 02 03 04 05 06 FF AA DB 02 03 04 05 06 FF AA DC 02 03 04 05 06 FF AA DD 02 03 04 05 06 FF AA DE 02 03 04 05 06 FF AA DF 02 03 04 05 06 FF AA E0 02 03 04 05 06 FF AA E1 02 03 04 05 06 FF AA E2 02 03 04 05 06 FF AA E3 02 03 04 05 06 FF AA E4 02 03 04 05 06 FF AA E5 02 03 04 05 06 FF AA E6 02 03 04 05 06 FF AA E7 02 03 04 05 06 FF AA E8 02 03 04 05 06 FF AA E9 02 03 04 05 06 FF AA EA 02 03 04 05 06 FF AA EB 02 03 04 05 06 FF AA EC 02 03 04 05 06 FF AA ED 02 03 04 05 06 FF AA EE 02 03 04 05 06 FF AA EF 02 03 04 05 06 FF AA F0 02 03 04 05 06 FF AA F1 02 03 04 05 06 FF AA F2 02 03 04 05 06 FF AA F3 02 03 04 05 06 FF AA F4 02 03 04 05 06 FF AA F5 02 03 04 05 06 FF AA F6 02 03 04 05 06 FF AA F7 02 03 04 05 06 FF AA F8 02 03 04 05 06 FF AA F9 02 03 04 05 06 FF AA FA 02 03 04 05 06 FF AA FB 02 03 04 05 06 FF AA FC 02 03 04 05 06 FF AA FD 02 03 04 05 06 FF AA FE 02 03 04 05 06 FF AA FF 02 03 04 05 06 FF

By comparison, I prefer choice commenting out the buffer full check.Because even if the data is lost, the data frame is more complete.But I don't know what happens to the other code if I commenting out the buffer full check.
By the way, uBit.serial.read( &data ,1, ASYNC) function, I have changed it according to the bug you submitted: while(bufferIndex < bufferLen && (temp = getChar(mode)) != MICROBIT_NO_DATA)

@zfm076
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zfm076 commented Mar 16, 2020

When the buffer is full, incoming bytes are dropped. When read() removes one byte, the next incoming byte will be added.

By commenting out the buffer full check, incoming bytes are overwriting old data. Data is still being lost. Reading will potentially get recent bytes followed by older ones.

Try sending frames with a counter, then see how the data looks:
0xFF 0x01 0x02 0x03 0x04 0x05 0x06 0xAA,
0xFF 0x02 0x02 0x03 0x04 0x05 0x06 0xAA,
0xFF 0x03 0x02 0x03 0x04 0x05 0x06 0xAA,
etc.

Serial works one byte at a time. Maybe set the buffer size to be a multiple of 8, check the size of the data available and read in multiples of 8.

Hi, martinwork. what happens to the other code if I commenting out the buffer full check？

@martinwork
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I'm sorry, I don't understand what you're asking. Did you reading 8 bytes at a time?

@zfm076
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zfm076 commented Mar 17, 2020

I'm sorry, I don't understand what you're asking. Did you reading 8 bytes at a time?

I reading 1 bytes at a time (uBit.serial.read( &data ,1, ASYNC);). Because it was the computer communicating with microbit, When my microbit handle serial port data, I judge the header bytes(0xAA) first. then The data is read until the end of the byte(0xFF) is read , Read through one frame and then process one frame of data. If a byte is lost in transit，I might not be able to read the correct data frame by reading 8 bytes. So I can't read 8 bytes at a time.

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