Various Projects for STM32F4 testing out ideas

• assembly: low level code,arm assembly to blink led
• blinky: simple project to get a led to blink on the board
• blinky_interupt: use systick(interupt) to blink led
  • GBD session: monitor arm semihosting enable
  • telnet session: arm semihosting enable
• led_switch: use switch on board to turn led on/off
• ext_led_switch: external push button connect on the GPIO to turn led on/off
• ext_interupt: using interrupts to light led on off using push button
• usart: use "polling" usart technique to print to serial console
• basic_timer: use general purpose timer to toggle led on pin PD15 via alternate function
• timer_interrupt_arr: use general purpose timer and ARR to generate interrupt