GPS reference clock NTP server with Gentoo

Posted on Feb 6, 2014

An L7805 provides a 5v rail. The input and output of the reg is bridged by a 470 F and a 10 F capacitor respectively to try and smooth things out a bit. The 5v rail created by the L7805 then powers the MAX232 level shifter and the GPS module itself. Thee light-duty transistors have their bases coupled to the TTL-side of the MAX232 PPS, TXD and R

GPS reference clock NTP server with Gentoo
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XD lines, which in turn drive three LEDs to give some indication that the device is doing what it should. Once the thing was proven to work, it was time to build a version small enough to squeeze along side the GPS module within Minion`s chassis. The same basic design was employed, but this time without the LEDs: Rather than using the external serial port, I made up a 10-pin PCB header cable to attach directly to the EPIA MII`s internal serial port. Overall the effect is quite pleasing: Power is taken from the spare molex provided by the PicoPSU`s trailing cable and attaches to a header directly infront of the reg. All in all, it has proved to be a suspiciously neat install! In order to take advantage of accurate PPS timing, the Linux kernel needs to be patched for PPS support. At the time of writing, the latest Gentoo kernel in Gentoo`s unstable branch is gentoo-sources-2. 6. 28-r2, so I`m going to work against that. The patch applied cleanly with me, so no additional fiddling around was required. Using your favourite kernel config method, make sure PPS support is enabled: PPS support [ ] Use low level IRQ timestamps [ ] PPS debugging messages * PPS clients support * Kernel timer client (Testing client, use for debug) PPS line discipline [ ] Parallel printer support # cd /usr/include # mv linux linux. old # mv asm asm. old # mv asm-generic asm-generic. old # ln -s /lib/modules/$(uname -r)/build/include/linux...

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