Notices by Lukas (karotte@chaos.social)

You may have heard of eUSB, the low-voltage cousin to the venerable USB 2.0 from 25 years ago. It's used on SoCs made on small process nodes that can't support standard USB 2.0 voltage levels.

Turns out, it recently got an upgrade called eUSB2V2 (yes, really). It supports asymmetric operation (which is a first for USB) at up to 4.8Gbit/s and is aimed at connecting high-resolution webcams in laptops.

@whitequark Thanks, that was quick!

@whitequark There was that silly meme comic about ASIC design "Reading LEG BoreSight documentation…" that I saw ages ago on twitter, but can't find it anymore. Do you happen to still have it somewhere?

If I²C was so good, why didn't they make I3C… oh wait they did!

First heard about it ~10 years ago and didn't think much of it as there wasn't any public documentation by the MIPI alliance.

Over the past few months however I noticed it popping up in SoC and sensors, so I had a closer look at what it is all about: 🧵 1/2

It's vaguely inspired by I²C and claims to be backwards-compatible with it by clock pulses being shorter than what the I²C spec permits, so I²C targets should ignore I3C traffic.

Addressing still happens in open-collector mode, but actual data transfer is done in push/pull mode at much higher speed. So no more clock streching, yay!

In-band interrupts are supported as well as canonical way to reset targets.

🧵 2/2

What's up with no(?) laptop vendor being able to fully specify the capabilities of USB-C ports?
No, "Tunderbolt™ 4 with USB4 Type-C® 40Gbps signaling rate (USB Power Delivery, DisplayPort™ 1.4) SuperSpeed USB 20Gbps is not available with Thunderbolt™ 4." Is totally not sufficient:

- What's the minium voltage/current required to charge?
- How much voltage/current can it source?
- Is 20Gbit/s USB available in non-TB4 mode?
- Which DisplayPort resolutions/refresh rates are supported? MST?

@0h00000000 I've long been waiting for an article like "Inventing USB alt modes for fun an profit". Potential candidates is everything that fits into 2/4 diffpairs, so
- PCIe
- SGMII/XGMII
- SATA

Since you invented the alt mode, you'd obviously have to supply both ends of it. Would still be an interesting exercise though.

If the folks that came up with the term "IP core" were given the chance to name other things:
- Books: IP words
- Music: IP notes
- Paintings: IP brush strokes

Was thinking about what sets apart Windows 11 from Windows 10 and came up with this helpful chart:

Ein netter Nebeneffekt des ETCS-Ausbaus im Ländle (digitaler Knoten Stuttgart) sind die zahlreichen veröffentlichten Fachpublikationen, die sonst nur Lesern der jeweiligen Zeitschriften vorbehalten wären: https://digitale-schiene-deutschland.de/de/mediathek/fachpublikationen

@whitequark
$ man ld
-l namespec Toggles linking the archive or object file specified by namespec. Specifying the same namespec an even number of times is therefore equivalent to not specifying it at all.

If an RF part is advertised as having "unmatched performance", is that a good or a bad thing? 🤔

Duckduck fedi, how does the android captive portal login browser work while still connected to mobile data?

The phone must be connected to the selected wifi, for the login to work, but the rest of the system still uses mobile data. What's the trick here? Spawning the captive portal browser in its own network namespace with a different default route?

After using the right screwdriver bit with Phillips and Pozidriv screws I came to realize that the bad reputation of cross-shaped screw drive may be based on the fact that many people used a wrong-sized bit or mixed up PH/PZ and got upset by the screwdriver camming out. Try using the right-sized bit and be amazed by how good cross-drive screws can be!

So perhaps Torx got its good rep not only by technical merit, but also by the fact that it's near-impossible to use a bit of the wrong size 🤔

@whitequark Connectors and other mechanical parts like switches are pretty amazing too.
I'm always surprised that the plastic housing just doesn't slide of the metal on pin headers and the like.

Turns out, it's worse than this: The ipv6-literal.net shenanigans aren't limited to UNC paths.

It works in all places:
> ping 2a0e-3c0--21.ipv6-literal.net

Pinging 2a0e:3c0::21 with 32 bytes of data:

Also works in browsers: http://2a0e-3c0--21.ipv6-literal.net/

Thanks to @casandro for asking.

Mildly cursed factoid about UNC paths:

- UNC Paths can contain IP addresses such as \\192.168.1.1\share
- IPv6 addresses are supported as well
- IPv6 addresses contain colons
- can't have colons in Windows paths since colons are reserved for drive letters

So Microsoft came up with the the ipv6-literal.net domain that's special-cased by Windows so you can to write IPv6 addresses in UNC paths as 2a0e-3c0--21.ipv6-literal.net without it hitting any resolvers.

Everyone has #blahaj, only me has MOROTHAJ 🥕🦈

@karotte's field guide to embedded CPU cores:

- does it have a USB connection? 8051
- does it handle USB power delivery? Cortex-M0
- does it process IP packets? MIPS
- is it in some sort of video ASIC? 80186

Yeah, seriously, what's up with the 80186? So far, I've encountered them in
- DP to HDMI converters (MCDP2900A)
- DVD Player SoCs (ZR36966)
- Monitor SoCs (STDP9310)

https://www.cpushack.com/2013/01/12/the-intel-80186-gets-turbocharged-vautomation-turbo186/ makes mention of two other video ASICs using an 80186 CPU

@whitequark So cool to see JTAG boundary scan being used outside of expensive in-circuit testers and the like!