Better Debugging of Embedded via a Debug Port ECE152

Overview  Why have a Debug Port?  What is a UART?  How does the Wunderboard UART work?  #DEFINE

What is a Debug Port?  JTAG  Digital Satellite, Later ECE courses  I2C  Proprietary  AVR serial ISP  Serial (UART)

Understanding Asynchronous Serial (UART)  Agreed on message format  Start and Stop Bits  Parity  Agreed on speed

AVR Hardware UART Peripheral

Handling a UART in software  Important Registers  USART I/O Data Register n– UDRn  USART Control and Status Register n A – UCSRnA  USART Control and Status Register n B – UCSRnB  USART Control and Status Register n C – UCSRnC  USART Baud Rate Registers – UBRRnL and UBRRnH

Baud Rate  Speed of transmission  Units of bits per second (bps or baud)

Start and Stop Bits  1 start bit, 1 or 2 stop bits USBSn bit in UCSRnC

FTDI UART to USB chip  Modern computers do not have RS232  USB to UART converters maintain a simple interface  FTDI Chip works on Windows, Mac and Linux  Often driverless installation  Can be disabled to allow for Wunderboard to Wunderboard serial communication

Voltages  Wunderboard  3.3V  FTDI  3.3 to 5V  Old School RS232  ±12V

Enabling and disabling Debug ports  Why Enable and Disable Debug?  Code Size  Code Speed  Security

#ifdef and Preprocessor Statements  Preprocessor statements happen BEFORE compilation #define DEBUG #ifdef DEBUG Serial code goes here... #ifdef

Things to Remember  Watch your flags to avoid buffer over run  Use #define to remove code before compilation