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MPC5744P LinFlex UART is very slow & possible fix

Question asked by Markus Ransberger on Oct 23, 2017
Latest reply on Oct 31, 2017 by Constantin Razvan Chivu



I just want to tell you that the LinFlex UART implementation is almost unusable slow. It takes around 250ms to transmit a hard-coded string of just 16 characters. That's 15.625ms per character. Can somebody please look into it for the next version?


So I went ahead and implemented the code of one of your C examples and voilà it actually takes around 2.2ms now to transmit about 20 characters.


In linflexd_pnt_library.c I replaced the "void linflexd_pnt_TxMsg(...)" function with the following:

void linflexd_pnt_TxMsg(uint8_t linflexd_unit, uint8_t *u8TxData,
        uint32_t u32Size) {
    uint8_t    j = 0; // Dummy variable


    for( j=0; j < u32Size; j++ )

        // Loop for character string  
        LINFlexD[linflexd_unit]->BDRL.B.DATA0 = *(u8TxData+j);
        //write character to transmit buffer
        while (1 != LINFlexD[linflexd_unit]->UARTSR.B.DTFTFF) {}
        // Wait for data transmission completed flag
        LINFlexD[linflexd_unit]->UARTSR.R = 0x0002;
        // clear the DTF flag and not the other flags


Since in the old function there is this code in it:

//       u32Cnt = 100000;
//       while ((UART_TX_FLAG == 0) && (u32Cnt > 0))/* Wait for Data to get transmitted */
//        { u32Cnt--; }

And this takes ages to complete.


Also in the "mbdtargetmainlibpnt.tlc" file, in the "void linflex_init_fnc(void)" function I commented out all of the timeout counter and output compare writes to the registers, but I did not test if this is necessary. (Now it's almost identical to the UART C example.)


Thank you again.


Best regards,

Markus Ransberger