Basic implementation of an escaping mechanism.

gistfile1.c

#define ESCAPE_CHAR 242
#define START_CHAR  0x7E
#define END_CHAR    0x0D

void usb_putc(uint8_t c);
uint8_t usb_getc();

void usb_escaped_putc(uint8_t c)
{
        switch(c) {
                case START_CHAR:
                case END_CHAR:
                case ESCAPE_CHAR:
                        usb_putc(ESCAPE_CHAR);
                        usb_putc(ESCAPE_CHAR^c);
                        break;
                default:
                        usb_putc(c);
        }
}

void usb_escaped_puts(uint8_t *b, unsigned int n)
{
        for(unsigned int = 0 ; i < n ; i++)
                usb_escaped_putc(b[i]);
}

void usb_get(uint8_t *buf)
{
        int i = 0;
        do{
                uint8_t c = usb_getc();
                switch(c) {
                        case ESCAPE_CHAR:
                                buf[i] = c;
                                buf[i++] ^= usb_getc();
                                break;
                        default:
                                buf[i++] = c;
                                break;
                }
        } while(buf[i-1]);
}