#include <avr/pgmspace.h>
#include <avr/io.h>
#include <stdbool.h>
#define F_CPU           8e6
#include <util/delay.h>

#define BAUD            9600
#define STOP_BITS       2
#define MARK            true                    // direct connection
//#define MARK            false                   // with Transceiver
#define STXD            SBIT( PORTB, 0 )
#define STXD_oe         SBIT( DDRB, 0 )

enum {TX_SRAM, TX_FLASH };

struct bits {
  uint8_t b0:1, b1:1, b2:1, b3:1, b4:1, b5:1, b6:1, b7:1;
} __attribute__((__packed__));
#define SBIT_(port,pin) ((*(volatile struct bits*)&port).b##pin)
#define SBIT(x,y)       SBIT_(x,y)

void sputchar(unsigned char c)
{
  c = ~c;                                       // complement to send 0 = stop bit(s)
  STXD_oe = 1;                                  // output
  STXD = MARK;                                  // start bit
  for (uint8_t i = 9 + STOP_BITS; i; i--)       // start + data + stop bits
  {
    _delay_us(1e6 / BAUD);                      // bit duration
    if (c & 1)
      STXD = MARK;
    else
      STXD = !MARK;                             // = Space
    c >>= 1;                                    // next bits or stop bit(s)
  }
}

void sputs(char *pt, uint8_t flag)
{
  uint8_t val;

  for (;;)
  {
    if (flag == TX_FLASH)
      val = pgm_read_byte(pt);
    else
      val = *pt;
    if (val == 0)
      return;
    sputchar(val);
    pt++;
  }
}

prog_char ftext[] = { "Text im Flash\n" };

int main(void)
{
  for (;;)
  {
    sputs(ftext, TX_FLASH);
    sputs("Text im SRAM\n", TX_SRAM);
    _delay_ms(1000);
  }
}