jdd: gpsd IS the application. It runs all the time providing time to NTP so that the system can be a stratum 1 time source. It is not started by an application. It should always be running. The application you referenced can of course talk to the GPS. The locations are not so accurate. They are what ever has come in on the serial port or perhaps the NMEA stream from gpsd. When you eventually read those locations and when you were actually at those locations are not the same. A simplified description is that the GPS pulses on the serial port when you are at a location it knows about internally but has not had a chance to communicate externally. Eventually, that location arrives in the NMEA stream. When it arrives is not deterministic. The GPS can have a delay. The baud rate can cause a delay. Process run states can have a delay. etc etc. But the PPS is a hardware interrupt with a pretty predictable latency. At least far better than hoping for the best reading the NMEA stream. Synchronizing time with a GPS is a totally different activity from just reading the locations as they come in. At least it is the case if you want accuracy. On Wed, Jan 14, 2015 at 5:40 PM, James Knott <james.knott@rogers.com> wrote:
On 01/14/2015 09:48 AM, Yamaban wrote:
RS232 was original defined as polling with hardware buffers only. During the later days of the ISA bus (ISA 32bit IIRC) there where cards available the generated a IRQ if new data arrived at the buffers.
That was the case with DOS, which had very poor com port support. Interrupts were common in mini and mainframe computers long before there was DOS & PC. I used interrupts for an 8 port serial card I designed for my IMSAI 8080, S-100 bus computer. That bus goes back to the Altair 8800 in 1974, which was 8 years before the IBM PC appeared.
One absolutely dumb thing IBM did with the PC was to use edge triggered interrupts, which made sharing them difficult. -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse+owner@opensuse.org
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