DN42, aka Decentralized Network 42, is a large VPN network. Unlike traditional VPNs, DN42 uses a lot of technology involved in Internet backbones (such as BGP) and is a great simulation of a realistic network environment.In a previous post (Chinese only), I joined DN42 and connected most of my VPSes to it. (The ones left are OpenVZ VPSes without Tun/Tap support.) I knew from the beginning that DN42 has its own domain name system. For example, DN42's wiki (https://wiki.dn42.us/Home) can be accessed as https://internal.dn42 in DN42. I didn't register a domain back then since I didn't have time, and I didn't have much knowledge of DN42. I finished the registration this month and would like to share my experience....

Our school organized a RoboMaster team and planned to attend the competition this year. Since we are all new students at a new campus, we do not have any reference materials available from previous students, and we have to figure out bugs after bugs on our own.This post describes some of the problems we met during software development.Hardware: RoboMaster Official Development BoardMCU Model: STM32F427IIHxSoftware: ChibiOS 18.2.0Board Has 12 MHz HSE Clock Instead of Commonly Seen 8MHzThe pitfall is that neither the manual nor the hardware schematics mentioned the clock frequency.Due to this problem, the actual frequency we programmatically set with STM32CubeMX or other software is much higher than expected. This caused the following problems:...

I wrote a PHP snippet to fetch high-resolution images from the website of the Himawari 8 satellite and combine them into one high-resolution image. The way to fetch satellite images is available here.However... The combined 4d resolution PNG image (2200x2200) is over 7 MB in size, and due to the bad connectivity between China and the US, it takes over a minute to load the image (from my server).Way too slow!Google provided a solution: the WebP image format. WebP is famous for its high compression ratio on lossless compression scenarios.After converting the 7 MB earth photo PNG file to WebP, the resulting file size is less than 700 KB. For a photo with resolution 2200x2200, this is pretty small.But... Some browsers, including IE and Firefox, don't support WebP,...

The Himawari 8 weather satellite is one of the Himawari satellites made by JAXA, weighs around 3500kg and has an expected lifespan of over 15 years. The satellite was successfully launched on October 7, 2014 with the H2A rocket and is mainly used to monitor storm clouds, tsunamis, and active volcanos.After launch, in addition to preventing natural disasters, Japan also released photos taken by the satellite on the Internet, which can be downloaded by enthusiasts. The photo is released on the official website at http://himawari8.nict.go.jp/m and is updated every 10th minute (like 9:30, 9:40...), with a 30-minute delay (the photo you see at 10:00 is taken at 9:30).Next, we're going to investigate how to obtain these pictures. With the network monitor functionality of the browser,...