nmea.h : NMEA parser
[/protocol : Collection of protocol related modules]

GPS NMEA protocol parser. More...

Data Structures
struct	nmea_data_t
	Parsed time, position, quality data. More...
Typedefs
typedef void(*	nmea_tx_byte_t )(u8_t data)
	Definition for a pointer to a function that will be called to send a character.
typedef void(*	nmea_on_valid_str_t )(const char *data)
	Definition for a pointer to a function that when a valid NMEA string is received.
typedef void(*	nmea_on_valid_gps_data_t )(void)
	Definition for a pointer to a function that will be called when GPS data is valid.
Functions
void	nmea_init (nmea_tx_byte_t tx_byte, nmea_on_valid_str_t on_valid_str, nmea_on_valid_gps_data_t on_valid_gps_data)
	Initialise NMEA parser module.
void	nmea_on_rx_byte (u8_t data)
	Function handler that is fed all raw received data.
void	nmea_tx_frame (char *frame)
	Function that is called to send an NMEA frame with the checksum appended.

---

Detailed Description

Files: nmea.h & nmea.c

See also:

http://en.wikipedia.org/wiki/NMEA_0183

---

Function Documentation

void nmea_init	(	nmea_tx_byte_t	tx_byte,
		nmea_on_valid_str_t	on_valid_str,
		nmea_on_valid_gps_data_t	on_valid_gps_data
	)

Parameters:

	tx_byte	Pointer to a function that will be called to transmit a byte.
	on_valid_str	Pointer to a function that will be called when a valid NMEA string has been received.
	on_valid_gps_data	Pointer to a function that will be called when the data structure has been completely polulated with valid data.

Definition at line 402 of file nmea.c.

{
    // Save function pointers
    nmea_tx_byte_fn           = tx_byte;
    nmea_on_valid_str_fn      = on_valid_str;
    nmea_on_valid_gps_data_fn = on_valid_gps_data;

   // Reset state variables
   nmea_rx_state            = NMEA_RX_STATE_START;
   nmea_rx_index            = 0;
   nmea_data.gga_valid_flag = FALSE;
   nmea_data.vtg_valid_flag = FALSE;
}

void nmea_on_rx_byte

(

u8_t

data

)

Parameters:

[in]

data

received 8-bit data

Definition at line 418 of file nmea.c.

{   
   switch(nmea_rx_state)
   {
   case NMEA_RX_STATE_START :
      {
         // Check start sequence
         if(data != '$')
         {
             break;
         }
         nmea_rx_state = NMEA_RX_STATE_PAYLOAD;
         // Reset index and checksum
         nmea_rx_checksum = 0;
         nmea_rx_index    = 0;
         return;
      }
   case NMEA_RX_STATE_PAYLOAD :
      {
         // Check for unexpected characters in payload
         if(  (data == '$' )
            ||(data == '\r')
            ||(data == '\n')
            ||(data >= 0x80)  )
         {
             break;
         }
         // Check for checksum marker
         if(data == '*')
         {
            nmea_rx_state = NMEA_RX_STATE_CHECKSUM1;
            return;
         }
         // Update checksum of payload
         nmea_rx_checksum ^= data;
         // Put received byte into buffer
         nmea_rx_buffer[nmea_rx_index] = data;
         // Check for buffer overflow
         if (++nmea_rx_index >= (NMEA_BUFFER_SIZE-1))
         {
             break;
         }
         return;
      }
   case NMEA_RX_STATE_CHECKSUM1 :
      {
         // Check high nibble of checksum
         if(!nmea_cmp_nibble_with_hex_ascii(((nmea_rx_checksum>>4)&0x0f), data))
         {
             break;
         }
         
         nmea_rx_state = NMEA_RX_STATE_CHECKSUM2;
         return;
      }
   case NMEA_RX_STATE_CHECKSUM2 :
      {
         // Check low nibble of checksum
         if(!nmea_cmp_nibble_with_hex_ascii((nmea_rx_checksum&0x0f),data))
         {
             break;
         }

         nmea_rx_state = NMEA_RX_STATE_END_CR;
         return;
      }
   case NMEA_RX_STATE_END_CR :
      {
         // Check Carriage Return
         if(data != '\r')
         {
             break;
         }
         nmea_rx_state = NMEA_RX_STATE_END_LF;
         return;
      }
    case NMEA_RX_STATE_END_LF:
      {
         // Check Line Feed
         if(data != '\n')
         {
             break;
         }
         // Append terminating zero
         nmea_rx_buffer[nmea_rx_index] = '\0';
         // String successfully received
         nmea_on_rx_frame((char*)nmea_rx_buffer);
         break;
      }   
   }
   // Error detected... reset receiver
   nmea_rx_state = NMEA_RX_STATE_START;
}

void nmea_tx_frame

(

char *

frame

)

Parameters:

frame

Pointer to zero terminated string.

Definition at line 512 of file nmea.c.

{
   u8_t  data;
   u8_t  checksum = '$';

   // Send data and calculate checksum
   while(*frame)
   {
       data      = *frame++;
       checksum ^= data;
       nmea_tx_byte(data);
   }

   // Add checksum
   nmea_tx_byte('*');
   // Send high nibble
   if(checksum<0xA0)
   {
       nmea_tx_byte(((checksum>>4)&0x0f)+'0');
   }
   else
   {
       nmea_tx_byte(((checksum>>4)&0x0f)+('A'-10));
   }
   // Send low nibble
   checksum &=0x0f;
   if(checksum<0x0A)
   {
       nmea_tx_byte(checksum+'0');
   }
   else
   {
       nmea_tx_byte(checksum+('A'-10));
   }

   // Add end sequence
   nmea_tx_byte('\r');
   nmea_tx_byte('\n');
}