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FirstGPS Starter Kit Overview
8
FirstGPS Starter Kit User Guide
The IO has a Pulse-per-Second (PPS) function. One of the IO pins is
held high for approximately 5 microseconds at the start of every UTC
second. An API call is available to apply a small time bias, typically
an advance of a few microseconds, to account for cable lengths.
The IO also has a temperature function. Inside the IO chip is a
temperature-sensitive counter. An API call provides the counts in real-
time, and the counts can be converted into temperature using a simple
formula.
1.2.2
FirstGPS Software
The FirstGPS software library is the GPS function software core.
It resides on the host CPU, so it shares RAM and ROM with the
customer’s application. The library must be compiled specific to each
application, depending on the CPU, Real-time Operating System
(RTOS), and compiler. The source code is very portable, written in C,
and it has been ported to a variety of different development
environments. The FirstGPS software library encompasses the
complete software interface with the IO chip, so the IO is essentially
transparent to the application software.
A complete list of API calls for the FirstGPS software library is listed
in Appendix A, Using the FirstGPS API. In general, the application
program uses the FirstGPS API calls to:
• Boot the IO and start the GPS function.
• Initialize the receiver with non-volatile memory and current
time, if available.
• Change receiver control parameters (satellite masks,
DGPS corrections).
• Fetch current receiver status.
• Fetch the most recent PVT solution.
• Fetch ancillary data (for example, signal strengths).
• Stop the GPS function.