It has been a while since my last log entry as I was working on other projects. During the past few weeks I set aside some time to work on the software needed for this project. I have been working on the routines needed to allow me to use the USI peripheral of the ATtiny45 to send and receive serial data. Three days ago I completed work on the sending routines and yesterday the receive routines started working.
I worked on the transmit routines first so they could be used during the testing of the receive routines. The first message the transmit routines sent was none other than the usual string "Hello, world!". :) This was sent at 4800 baud once a second. Yesterday the transmit routine was showing me that a "$" character was being received. It is a very good indication that the receive routine is working properly.
I already had the routines required to process the NMEA messages I'm expecting. I set up the main program to wait for the messages I need from the GPS receiver module before it would send any data. I use a Raspberry Pi to to monitor the serial data stream and I'm seeing characters being output once per second. Another good sign that I'm receiving the NMEA data from the GPS module and raising the flags that tell me when I have received both messages.
The data transmitted after receiving the NMEA messages is not what I should be seeing. I need to do more tests to determine why I'm not seeing what I expect to see. Overall I'm pleased with the progress I've made on the software. I'm close to having the basic features implemented to have a fully working prototype.