Introduction

Teensy-utils is a collection of useful modules for writing AVR applications in C, and on the Teensy microcontroller in particular. All of this code has been developed against an ATmega32U4, patches are welcome to generalize the code for other Atmel chips.

Using Modules

To use a module in your code, simply checkout teesny-utils into a subdirectory of your project (e.g. teensy_utils/), and include the corresponding .c file for each module you use in the SRC variable of your make file. For example:

SRC = $(TARGET).c \
      teensy_utils/timer.c \
      teensy_utils/lock.c

Demo Code

To build demo apps for each module, simply run the associated makefile:

make -f timer.mk

See corresponding demo file for explanation of the demo program.

Modules

Timer

The timer module provides a real-time counter with 100µs resolution using Timer 3. Applications may use it from within an event loop to execute code on a periodic basis. Applications may poll to determine if their timer has fired and perform an associated action. For example,

int main(void)
{
  timer_t timer1, timer2, timer3;

  sei();
  setup_timer(); //Real-time clock

  init_timer(&timer1, 5000);  //5000 'ticks' == 500ms
  init_timer(&timer2, 10000); 
  init_timer(&timer3, 8000);

  while(1) {
    if(timer_fired(&timer1)) {
      LED_TOGGLE; //Toggles every 500ms
    }

    if(timer_fired(&timer2)) {
      printf("Fizz"); //Is printed every 1 second
    }
    if(timer_fired(&timer3)) {
      printf("Buzz"); //Is printed every 800ms
    }
  }
}

The timer has 16-bit precision and thus "rolls over" every 6.55 seconds. timer_fired() must be called every ~3.27 seconds for each timer or firings will be lost.

Lock

This module allows different modules to share access to a single resource, e.g. the SPI or USB interface. Modules may then start a long running operation on the interface and release the lock once it is completed.

API TBD

SPI

SPI is a module for using the SPI interface in master mode to transmit data. It allows code to send a complete buffer and poll for the completion. The code handles the assertion of the SS pin for the peripheral you wish to communicate with, lowering it at the start of transfer and raising it at the end. Configuration of the SS-pin and (in the future) SPI parameters is done via a special struct in program memory.

static const spi_peripheral_cfg spi_cfg PROGMEM = {
    .port_register = &PORTB,
		.pin_mask      = 0b00000001 //SS is B0
	};

int main(void) {
  uint8_t buf[] = "HELLO WORLD";
  setup_spi(); //Initialize the SPI module

  //Writes 12 bytes out the SPI interface, buf is overwritten with the data read
  async_rw_spi(&spi_cfg, buf, 12); 
  
  while(has_spi(&spi_cfg)); //Spin until this transfer is done
}