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printf() with the FRDM-KL25Z Board and without Processor Expert

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printf() with the FRDM-KL25Z Board and without Processor Expert

· Performance Zone ·
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In this tutorial I explored how to use printf(), and this tutorial is so generic that it works for any processor/microcontroller. That flexibility is because I’m using Processor Expert. In case Processor Expert shall not be used, then some tweaks are needed. Here I show what is needed to have printf() working with the FRDM-KL25Z board. I use the UART0 connected to OpenSDA USB CDC for this.

Creating the Project

I create a new bareboard project. Nothing special here, except that ‘UART’ should be selected:

UART set for new project settings

UART set for new project settings

Low Level UART Support

As explained in this tutorial I, I need low-level UART support. CodeWarrior comes with the needed files for the TWR-KL25Z in “\MCU\ARM_GCC_Support\UART\TWR-KL25Z128″:

Low Level UART support files

Low Level UART support files

I copy these files into my project:

Copied Low Level UART Support Files

Copied Low Level UART Support Files

The TWR-KL25Z is using UART0 with PTA14/PTA15, while the FRDM-KL25Z is using UART0, but PTA1/PTA2. So I need to change the pin settings.

For this I disable in ConsoleIO.c, in ConsoleIO_Init() the settings for the Tower board, and add my change to use PTA1/PTA2:

void ConsoleIO_Init()
    /* SIM_SCGC4: UART0=1 */
#if 0 /* TWR version: PTA14, PTA15 */
    /* PORTA_PCR15: ISF=0,MUX=3 */
    PORTA_PCR15 = (uint32_t)((PORTA_PCR15 & (uint32_t)~(uint32_t)(
                 PORT_PCR_ISF_MASK |
                )) | (uint32_t)(
    /* PORTA_PCR14: ISF=0,MUX=3 */
    PORTA_PCR14 = (uint32_t)((PORTA_PCR14 & (uint32_t)~(uint32_t)(
                 PORT_PCR_ISF_MASK |
                )) | (uint32_t)(
#else /* FRDM-KL25Z: PTA1/PTA2 */
      /* PORTA_PCR1: ISF=0,MUX=2 */
      PORTA_PCR1 = (uint32_t)((PORTA_PCR1 & (uint32_t)~0x01000500UL) | (uint32_t)0x0200UL);
      /* PORTA_PCR2: ISF=0,MUX=2 */
      PORTA_PCR2 = (uint32_t)((PORTA_PCR2 & (uint32_t)~0x01000500UL) | (uint32_t)0x0200UL);
    UART0_PDD_EnableTransmitter(UART0_BASE_PTR, PDD_DISABLE); /* Disable transmitter. */
    UART0_PDD_EnableReceiver(UART0_BASE_PTR, PDD_DISABLE); /* Disable receiver. */
    /* UART0_C1: LOOPS=0,DOZEEN=0,RSRC=0,M=0,WAKE=0,ILT=0,PE=0,PT=0 */
    UART0_C1 = 0x00U;                    /*  Set the C1 register */
    /* UART0_C3: R8T9=0,R9T8=0,TXDIR=0,TXINV=0,ORIE=0,NEIE=0,FEIE=0,PEIE=0 */
    UART0_C3 = 0x00U;                    /*  Set the C3 register */
    UART0_S2 = 0x00U;                    /*  Set the S2 register */
    UART0_PDD_SetBaudRate(UART0_BASE_PTR, 313U); /* Set the baud rate register. */
    UART0_PDD_SetOversamplingRatio(UART0_BASE_PTR, 3U);
    UART0_PDD_EnableSamplingOnBothEdges(UART0_BASE_PTR, PDD_ENABLE);
    UART0_PDD_EnableTransmitter(UART0_BASE_PTR, PDD_ENABLE); /* Enable transmitter */
    UART0_PDD_EnableReceiver(UART0_BASE_PTR, PDD_ENABLE); /* Enable receiver */

:idea: To use different UART/port settings, the easiest way is to use a Processor Expert project as explained in this tutorial.

Example Code

For testing, I print a ‘hello world’ from the main() in main.c:

 * main implementation: use this 'C' sample to create your own application
#include "derivative.h" /* include peripheral declarations */
#include "ConsoleIO.h"
int main(void)
    int counter = 0;
    for(;;) {
        printf("Hello world!\r\n");
    return 0;

:!: Do not forget to include the correct header files, and to call ConsoleIO_Init()!

That’s it! Build, download and hopefully you see the messages printed to the console :-) .

Project on GitHub

For reference, I have committed the CodeWarrior project and sources on GitHub here.

Happy Printing :-)


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