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TM4C123G cheat sheet

Introduction

This page contains snippets of code used to initialize specific functions of the Texas Instruments TM4C123GH6PM microcontroller. It assumes the presence of the tm4c123gh6pm.h header file for the definition of the constants.

Open-source toolchain

On-board debugging

You need a .AXF with debugging information in it (build sources with -g).

  1. Step 1: start OpenOCD:
    /Applications/GNU\ ARM\ Eclipse/OpenOCD/0.10.0-201601101000-dev/bin/openocd -f /Applications/GNU\ ARM\ Eclipse/OpenOCD/0.10.0-201601101000-dev/scripts/board/ek-tm4c123gxl.cfg
  2. Step 2: start GDB:
    arm-none-eabi-gdb bin/netradio.axf
    where bin/netradio.axf is the .AXF that you want to debug on the board.
  3. Step 3: connect to the board:
    (gdb) target extended-remote :3333
  4. Step 4: download the program to the board:
    (gdb) load
  5. Step 5: set a breakpoint at main:
    (gdb> break main
  6. Step 6: start the program:
    (gdb) c

GPIO port initialization: digital output

  volatile unsigned long delay;
  SYSCTL_RCGC2_R |= SYSCTL_RCGC2_GPIOx;    // activate port x  (x = A...F)
  delay = SYSCTL_RCGC2_R;      // allow time for clock to stabilize
  GPIO_PORTx_DIR_R |= ... ;    // set pins as output
  GPIO_PORTx_AMSEL_R &= ~...;  // disable analog functions 
  GPIO_PORTx_AFSEL_R &= ~...;  // disable alternative functions 
  GPIO_PORTx_DEN_R |= ... ;    // enable digital I/O on selected ports

GPIO port initialization: digital input

  volatile unsigned long delay;
  SYSCTL_RCGC2_R |= SYSCTL_RCGC2_GPIOx;    // activate port x  (x = A...F)
  delay = SYSCTL_RCGC2_R;      // allow time for clock to stabilize
  GPIO_PORTx_DIR_R &= ~... ;   // set pins as input
  GPIO_PORTx_AMSEL_R &= ~...;  // disable analog functions 
  GPIO_PORTx_AFSEL_R &= ~...;  // disable alternative functions 
  GPIO_PORTx_PUR_R |= ...;     // enable pull-up resistors for input pins (PDR for pull down)
  GPIO_PORTx_DEN_R |= ... ;    // enable digital I/O on selected ports

GPIO port initialization: analog input (ADC)

The ADC description starts on page 799 of the TM4C123GH6PM datasheet.

Initialization:

  volatile unsigned long delay;
  // Configure PE2 as Ain1
  SYSCTL_RCGC2_R |= 0x10;
  delay = SYSCTL_RCGC2_R;
  GPIO_PORTE_DIR_R &= ~0x04;   // PE2 (Ain1) = input
  GPIO_PORTE_AFSEL_R |= 0x04;  // alt. function for PE2
  GPIO_PORTE_DEN_R &= ~0x04;  // disable digital I/O on PE2
  GPIO_PORTE_AMSEL_R |= 0x04;  // analog function for PE2
  // Activate & configure ADC0 with Ain1
  SYSCTL_RCGC0_R |= 0x00010000;  // activate ADC0
  SYSCTL_RCGC0_R &= ~0x0300;  // configure for 125K
  ADC0_SSPRI_R = 0x0123;     // sequencer 3 is highest priority
  ADC0_ACTSS_R &= ~0x08;     // disable SS3 for config
  ADC0_EMUX_R &= ~0xF000;    // config SS3 as software trigger
  ADC0_SSMUX3_R = (ADC0_SSMUX3_R & 0xFFFFFFF0) + 1;  // use channel Ain1 (PE2)
  ADC0_SSCTL3_R = 0x06;
  ADC0_ACTSS_R |= 0x08;  // enable SS3

Active wait:

  unsigned long result;
  ADC0_PSSI_R = 0x08;   // start SS3
  while ((ADC0_RIS_R & 0x08) == 0);  // wait until sampling done
  result = (ADC0_SSFIFO3_R & 0x0FFF);  // read result

SysTick initialization and use

With interrupt

Initialization:

  NVIC_ST_CTRL_R = 0;
  NVIC_ST_RELOAD_R = x;   // x = reload value
  NVIC_ST_CURRENT_R = 0;
  NVIC_SYS_PRI3_R = NVIC_SYS_PRI3_R & 0X00FFFFFF;  // priority 0
  NVIC_ST_CTRL_R = 0x07;  // enable with core clock and interrupts

Interrupt handler:

void SysTick_Handler(void) {
  ...
}

With active wait

Initialization:

  NVIC_ST_CTRL_R = 0;
  NVIC_ST_CTRL_R = 0x05;

Wait:

  NVIC_ST_RELOAD_R = x-1;  // x = countdown value
  NVIC_ST_CURRENT_R = 0;
  while ((NVIC_ST_CTRL_R & 0x00010000) == 0);