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J-Link Compact USB-C Issues
- pcdoodle 1y agoDid I get this right? some cables have an MCU that gets power through a 1K series resistor on CC2? That MCU also sources ground through the cables GND?
- fhars 1y agoUSB3 cables are black magic, anyway.
- lxgr 1y agoContrary to many other electronics standards, the USB-C spec is just a free download away.
- bloggie 1y agoYes and this is a requirement for many different connection modes. https://en.wikipedia.org/wiki/USB-C#E-Mark https://en.wikipedia.org/wiki/USB-C#E-Mark
- alvarop 1y agoThe 1k resistor just lets the device know there’s an MCU on that line. The device would then provide power on that pin before talking to it
- jmux 1y agoThe USB-C step is humongous, and hard to implement. the complexity is high, but how else can you tell a cable that supports USB4 (40GBps) from one that’s only good for charging your phone (and everything in between)? users aren’t going to be able to tell the difference (using a cable with no data lines is already a super common issue with people getting into MCUs) so the device needs to be able to tell how much data and power the connected cable can distribute automatically. this also why usb-c extension cables (M-F) aren’t spec complaint it’s a real cool port, but the complexity demon is definitely present in the spec :)
- userbinator 1y agobut how else can you tell a cable that supports USB4 (40GBps) from one that’s only good for charging your phone (and everything in between)? By attempting to link up at the highest supported speed and downshifting if there's no valid signal? Ethernet had this figured out decades ago.
- lxgr 1y agoUSB-C doesn’t only carry USB data. I’m not sure if e.g. Displayport even has the capacity for link training (and there are USB-C to Displayport cables that have to support legacy devices that know nothing about USB); HDMI (until 2.2 or so) definitely does not. It’s ok to not agree with the USB-IF’s tradeoffs in their solutions, but denying the complexity of the problem space can be a hint that you don’t sufficiently understand it to pass that kind of judgement.
- jauntywundrkind 1y agoIntel has a flow for how link training is done on DisplayPort. Probably shouldn't be surprised but it involves communicating over the AUX channels. Is this something that a sizable % of computers can do? For some reason I thought aux channel was semi free for use, that it could be for Ethernet or USB in a pretty naked form. Didn't realize that needed mode switching? https://www.intel.com/content/www/us/en/docs/programmable/683273/22-2-20-0-1/displayport-link-training-flow.html https://www.intel.com/content/www/us/en/docs/programmable/68...
- lxgr 1y agoAh, so maybe DisplayPort has mandatory link training then, which would indeed allow unmarked cables. But to GPs point, there still needs to be a way to tell the source that a given cable is a USB-C-to-DisplayPort one in the first place. So why not include the metadata on what signal grades it’s rated for in that same indicator? That’s exactly what e-markers are.
- userbinator 1y ago
- jrockway 1y agoHonestly no excuse for this to be done wrong on a $400 device. They should replace all deployed units for free. (Because you know these cost $20 to make.)
- userbinator 1y agoBecause no one really understands USB-C... The price is not too surprising --- the margins are insane on many embedded development tools, although the stuff coming out of China is slowly trying to change that. The most expensive part of this device is the MCU which is around $15, but comparable ones from other manufacturers are <$5.
- lxgr 1y agoPlenty of manufacturers understand USB-C well enough to get this right. Out of what must be dozens, I own a total of two devices, and have encountered one more, that have this kind of mistake in their design; except for the Raspberry Pi 4, I’m not surprised based on the quality and price of the device.
- 05 1y agoI'm sorry but the CC1/CC2 pullup issue is so widespread any electronics engineer getting that wrong now has no business designing USB devices
- eschneider 1y agoTBF, I paid about twice that for the JLink model I have and I've gotten value for money. I'm not complaining.
- jrockway 1y agoYeah, the sticker that says "J-Link" is the expensive part. That's why $1.99-on-AliExpress level hardware mistakes are inexcusable. (I mean, a bug is a bug, they happen. But you've gotta make it right.)
- userbinator 1y agoThis means there’s a small microcontroller inside the cable with information on the cable’s capabilities. More evidence that USB-C is an insanely overengineered spec. Cables should be dumb pipes, not devices with their own active circuitry. IMHO Ethernet, while not perfect, got this part right. The only reason the signals don’t exactly match the one above is just the orientation of the cable. This is one of the more perplexing design decisions. Was simply mirroring the contacts too simple for them? Did someone imagine a use-case where they wanted to detect the orientation of the cable? WTF.
- paholg 1y agoEthernet doesn't support 240 W. I am very happy that I can charge my phone and laptop from the same charger, and don't ever have to worry about whether the cable I'm using will be a fire hazard.
- deleted 1y ago[deleted]
- userbinator 1y agoPoE has been around for longer, and while it doesn't go that high (90W --- but at much longer distances), it uses passive cables just fine.
- fooblaster 1y agoPOE is an quite expensive thing to implement on a board. Flyback transformers are essentially required to support the standard.
- lxgr 1y agoAt the cost of much higher complexity on each end. USB-C still supports completely passive old chargers and devices.
- chongli 1y agoThe cable can still be a fire hazard if it’s a cheap cable that lies about its rated wattage, no?
- lxgr 1y agoSame (or very similar) problem as for early Raspberry Pi, as far as I remember.
- stickfigure 1y agoIs there some device I can buy that lets me plug in a USB-C cable and tells me the capabilities of the cable? I have a giant stack of cables and it would be nice to know what they can do.
- deleted 1y ago[deleted]
- StrangeDoctor 1y agohttps://hackaday.com/2023/08/11/usb-c-cable-tester-is-compact-and-affordable/ https://hackaday.com/2023/08/11/usb-c-cable-tester-is-compac... These sorts of devices can tell you how a cable is wired up, which is great for a a first pass or spot checking.
- simjnd 1y agoCould this be done in software? I'm very uneducated on the topic but doesn't your computer need to know the capabilities of a cable when it's plugged in? (USB speed, PD support, etc.)
- lxgr 1y agoAt least for e-marked cables, this seems possible, and once the other side is plugged in at well, it should be clear to the controller what it is and what type of cable connects the two devices (only 2.0 cables supporting at least 3A/20V are allowed to not have a marker per the spec). No idea why this is not a thing on most devices.
- Aaargh20318 1y agoFNIRSI FNB58 might do what you want.
- shadowpho 1y agohttps://a.co/d/2OMfGrg https://a.co/d/2OMfGrg Here you go, I got this guy and it’s fantastic. Tells me pd capabilities, voltage/current and resistance.
- 8zah6q7 1y ago
- kotaKat 1y agoI'm so tired of bad USB-C implementations. I wish the EC didn't shove their heads up their ass to give us such an unreliable connector on our mobile devices throughout the world.