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hello.ftdi.44.echo.c

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  • hello.ftdi.44.echo.c 4.73 KiB
    //
    //
    // hello.ftdi.44.echo.c
    //
    // 115200 baud FTDI character echo
    //
    // set lfuse to 0x5E for 20 MHz xtal
    //
    // Neil Gershenfeld
    // 12/8/10
    //
    // (c) Massachusetts Institute of Technology 2010
    // This work may be reproduced, modified, distributed,
    // performed, and displayed for any purpose. Copyright is
    // retained and must be preserved. The work is provided
    // as is; no warranty is provided, and users accept all 
    // liability.
    //
    
    #include <avr/io.h>
    #include <util/delay.h>
    #include <avr/pgmspace.h>
    
    #define output(directions,pin) (directions |= pin) // set port direction for output
    #define set(port,pin) (port |= pin) // set port pin
    #define clear(port,pin) (port &= (~pin)) // clear port pin
    #define pin_test(pins,pin) (pins & pin) // test for port pin
    #define bit_test(byte,bit) (byte & (1 << bit)) // test for bit set
    #define bit_delay_time 8.5 // bit delay for 115200 with overhead
    #define bit_delay() _delay_us(bit_delay_time) // RS232 bit delay
    #define half_bit_delay() _delay_us(bit_delay_time/2) // RS232 half bit delay
    #define char_delay() _delay_ms(10) // char delay
    
    #define serial_port PORTA
    #define serial_direction DDRA
    #define serial_pins PINA
    #define serial_pin_in (1 << PA0)
    #define serial_pin_out (1 << PA1)
    
    #define max_buffer 25
    
    void get_char(volatile unsigned char *pins, unsigned char pin, char *rxbyte) {
       //
       // read character into rxbyte on pins pin
       //    assumes line driver (inverts bits)
       //
       *rxbyte = 0;
       while (pin_test(*pins,pin))
          //
          // wait for start bit
          //
          ;
       //
       // delay to middle of first data bit
       //
       half_bit_delay();
       bit_delay();
       //
       // unrolled loop to read data bits
       //
       if pin_test(*pins,pin)
          *rxbyte |= (1 << 0);
       else
          *rxbyte |= (0 << 0);
       bit_delay();
       if pin_test(*pins,pin)
          *rxbyte |= (1 << 1);
       else
          *rxbyte |= (0 << 1);
       bit_delay();
       if pin_test(*pins,pin)
          *rxbyte |= (1 << 2);
       else
          *rxbyte |= (0 << 2);
       bit_delay();
       if pin_test(*pins,pin)
          *rxbyte |= (1 << 3);
       else
          *rxbyte |= (0 << 3);
       bit_delay();
       if pin_test(*pins,pin)
          *rxbyte |= (1 << 4);
       else
          *rxbyte |= (0 << 4);
       bit_delay();
       if pin_test(*pins,pin)
          *rxbyte |= (1 << 5);
       else
          *rxbyte |= (0 << 5);
       bit_delay();
       if pin_test(*pins,pin)
          *rxbyte |= (1 << 6);
       else
          *rxbyte |= (0 << 6);
       bit_delay();
       if pin_test(*pins,pin)
          *rxbyte |= (1 << 7);
       else
          *rxbyte |= (0 << 7);
       //
       // wait for stop bit
       //
       bit_delay();
       half_bit_delay();
       }
    
    void put_char(volatile unsigned char *port, unsigned char pin, char txchar) {
       //
       // send character in txchar on port pin
       //    assumes line driver (inverts bits)
       //
       // start bit
       //
       clear(*port,pin);
       bit_delay();
       //
       // unrolled loop to write data bits
       //
       if bit_test(txchar,0)
          set(*port,pin);
       else
          clear(*port,pin);
       bit_delay();
       if bit_test(txchar,1)
          set(*port,pin);
       else
          clear(*port,pin);
       bit_delay();
       if bit_test(txchar,2)
          set(*port,pin);
       else
          clear(*port,pin);
       bit_delay();
       if bit_test(txchar,3)
          set(*port,pin);
       else
          clear(*port,pin);
       bit_delay();
       if bit_test(txchar,4)
          set(*port,pin);
       else
          clear(*port,pin);
       bit_delay();
       if bit_test(txchar,5)
          set(*port,pin);
       else
          clear(*port,pin);
       bit_delay();
       if bit_test(txchar,6)
          set(*port,pin);
       else
          clear(*port,pin);
       bit_delay();
       if bit_test(txchar,7)
          set(*port,pin);
       else
          clear(*port,pin);
       bit_delay();
       //
       // stop bit
       //
       set(*port,pin);
       bit_delay();
       //
       // char delay
       //
       bit_delay();
       }
    
    void put_string(volatile unsigned char *port, unsigned char pin, char *str) {
       //
       // print a null-terminated string
       //
       static int index;
       index = 0;
       do {
          put_char(port, pin, str[index]);
          ++index;
          } while (str[index] != 0);
       }
    
    int main(void) {
       //
       // main
       //
       static char chr;
       static char buffer[max_buffer] = {0};
       static int index;
       //
       // set clock divider to /1
       //
       CLKPR = (1 << CLKPCE);
       CLKPR = (0 << CLKPS3) | (0 << CLKPS2) | (0 << CLKPS1) | (0 << CLKPS0);
       //
       // initialize output pins
       //
       set(serial_port, serial_pin_out);
       output(serial_direction, serial_pin_out);
       //
       // main loop
       //
       index = 0;
       while (1) {
          get_char(&serial_pins, serial_pin_in, &chr);
          put_string(&serial_port, serial_pin_out, "hello.ftdi.44.echo.c: you typed \"");
          buffer[index++] = chr;
          if (index == (max_buffer-1))
             index = 0;
          put_string(&serial_port, serial_pin_out, buffer);
          put_char(&serial_port, serial_pin_out, '\"');
          put_char(&serial_port, serial_pin_out, 10); // new line
          }
       }