www.pudn.com > SerialGPS.zip > ReadPacket.m

function [id, data] = ReadPacket(gps, type) 
% READPACKET Read a single packet from the device 
 
global pid_ack_byte pid_nak_byte 
 
if (nargin < 2) 
    type = 'uint8'; 
end 
 
% Initialize output data 
data = []; 
 
% Read the packet header (id and size) 
[id, sz] = ReadPacketHeader(gps);  
 
% Read data, if non-zero size     
if (sz > 0) 
    [data, d] = ReadData(gps, id, sz / sizeof(type), type); 
end 
 
% Read checksum and packet terminator 
cksum = ReadPacketTerminator(gps); 
 
% Verify checksum  
csum = ComputeChecksum(id, d); 
if (csum ~= cksum) 
    WritePacket(gps, pid_nak_byte, id); 
    error(['Checksum mismatch. Got ', num2str(cksum), ', expecting ', num2str(csum)]); 
end 
 
% Send ACK, unless we just read an ACK or NAK 
if ((pid_ack_byte ~= id) && (pid_nak_byte ~= id)) 
    WritePacket(gps, pid_ack_byte, id); 
end