Recent content on niconiconi's blog
Abstract In a WeChat article titled How Large is the Phase Error of Commercially Available VNA Open and Short Calibration Kits? [1], a vendor claimed to have measured cheap, generic Vector Network Analyzer (VNA) calibration kits (“calkit”) commonly used in amateur radio, asserting they have errors of “tens, even hundreds of degrees.” However, the measurement data published by the vendor violates…
The following circuit is the well-known infinite ladder network, constructed by repeatedly adding a series impedance 𝑍sZs and a parallel impedance 𝑍pZp. The reader may question the usefulness of such a circuit, which appears to possess the sole purpose of nerd-sniping. While this is indeed its common usage, but it does have quite a few practical applications. Physically, a discrete circuit has a…
Introduction In 2021, at the height of cryptocurrency mining, Nvidia released the Nvidia CMP 170HX. Designed as a compute-only card to accelerate Ethereum’s memory-hard Ethash Proof-of-Work mining algorithm with its 1500 GB/s HBM2e memory bus, Nvidia implemented the hardware using the GA100 silicon from their Ampere architecture. Thus, the CMP 170HX is essentially a variant of the all-mighty…
Or: How to avoid 4000% performance degradation if I use HIP Managed Memory Introduction On AMD GPUs, the feature XNACK is essential for running HIP code that uses Managed Memory, or running SYCL code that uses Unified Shared Memory (USM). Performance can degrade by as much as 4000% without XNACK. Exactly what XNACK does, or how can it be enabled, is poorly documented in all but a few places. I…
Abstract On iOS, background audio autoplay is disallowed, users are not even allowed to add exceptions. Thus, many existing Web apps and games - WebAssembly apps in particular, are incompatible with iOS without modifications. Fortunately, iOS 15 (late 2021) started to allow browser extensions, including Userscripts. To overcome this problem, a Userscript has been developed to intercept Web Audio…
Pictured: Electric field lines of a microstrip transmission line over a ground plane. Image from Grounding and Shielding: Circuits and Interference by Ralph Morrison. Introduction In this article, a method of cross-compiling FORTRAN code to WebAssembly with LLVM and flang is described. Since WebAssebly uses 32-bit pointers, but 32-bit platforms are not supported by flang, currently, only numerical…
Introduction Unix pioneer Ken Thompson’s 1983 Turing Award acceptance speech popularized the now well-known concept of a Reflections on Trusting Trust-style backdoor, or in my words, a meta-backdoor. He argued that even a complete code audit cannot always ensure that a program is backdoor-free, since the development tools in the system can themselves be backdoored, and thus, implanting…
Introduction Recently, I’ve purchased a vintage Hewlett-Packard 436A RF power meter and a HP 8484A power sensor for testing a circuit I’m building. Since the measurement I’m trying to do is delicate, on the order of 0.1 dB, I need to estimate my measurement accurary and to understand the sources of uncertainties. In this article, the main sources of uncertainties in RF and…
Introduction As a retrocomputing and electronics enthusiast, there are several vintage computer chips in my collection. Chips Zilog Z80 Production Date: 1999, 21th week. Purchase Date: 2020-04 Mastodon post: link After two engineers left Intel in the 1970s, a startup company named Zilog soon released a new microprocessor as the company’s first product - Zilog Z80. Designed by Federico Faggin…
Introduction The Analog-to-Digital Converters (ADC) in most microcontrollers (MCU) are slower than 1 Msps since their primary application is relatively slow automatic control and measurements, not the fast data acquisition and processing at high rates. In fact, the limited CPU speed and memory size of many microcontrollers are incapable of keeping up with a faster ADC, necessitates the use of a…
Image by Don DeBold, CC BY 2.0, some rights reserved. Introduction For fun, I’m implementating the ChaCha20 cipher in PDP-11 assembly. To maximize its compatibility, my primary reference target is a plain PDP-11/40 without the Extended Instruction Set (EIS) option nor speedups available in later machines. Backward compatibility is also provided for PDP-11/20 to cover 100% of the…
Creating, rewriting, and abolishing one’s blog or homepage, before starting a new one again - usually also changing themes, blog engines, servers (or even writing one’s own blog engine if you are a web-type person - I’m not). …This is all too common in tech. I’m not an exception to the rule. So here’s my new blog. I hope you enjoy my occasional technical…