What follows is the story of how I fixed not one, but two, different flawed Altera USB Blaster clone devices that never worked correctly after I bought them.

I recently built a few Time Sleuths for HDMI input lag testing. Time Sleuth is a neat little open-source project that allows you to measure the time it takes for your TV or monitor to display an image. The way it works is an Altera/Intel MAX 10 FPGA creates a video signal that is mostly a black screen with some blinking white boxes. It feeds the image off to a TI TFP410 DVI transmitter, and also looks for a pulse on a photodetector. It measures the difference in time between when the white box blinked on and the photodetector saw it, and displays it as a number on its generated video signal with some min/max/average stats. Pretty cool! If you’re not into soldering, you can also buy them fully assembled.

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I’m going to start this post off with the obligatory list of links to the previous parts in the series if you’re new here and are interested in seeing the full story: 1, 2, 3, 4, 5, 6, 7, 8, and 9. This is the tale of how I upgraded my Chumby 8 to run a modern Linux kernel.

I only had some minor things on my list to figure out before I could call my kernel upgrade good enough to be finished. The most important remaining thing was the real-time clock, or RTC. I noticed that whenever I rebooted the Chumby, it always started out with the date set to the Unix epoch in 1970:

# date
Thu Jan 1 00:00:12 UTC 1970

I had observed earlier that the default pxa168.dtsi file in the kernel had an RTC already added, but it was disabled:

rtc: rtc@d4010000 {
compatible = "mrvl,mmp-rtc";
reg = <0xd4010000 0x1000>;
interrupts = <5>, <6>;
interrupt-names = "rtc 1Hz", "rtc alarm";
clocks = <&soc_clocks PXA168_CLK_RTC>;
resets = <&soc_clocks PXA168_CLK_RTC>;
status = "disabled";
};

Would it really be this simple? Did I just need to enable the RTC in my device tree file, make sure the kernel driver was enabled, and then be done with it? I had already experienced similar success with other PXA168 peripherals. So I tried it out.

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