Haha, I'm still over here messing with 10/100 Ethernet and USB 2 on my home projects. I'm used to bigger tolerances than the truly high tech stuff.
Comment on iFixit hails replaceable LPCAMM2 laptop memory as a 'big deal'
SpaceNoodle@lemmy.world 1 week agoA millimeter is huge in these situations. USB3 requires 5 mil tolerances, just over 0.1 mm. This scales with the inverse of data rate.
Electronics are so fast that we gotta take the speed of light into account. God help you if you put too sharp a bend in a trace, too …
TimeSquirrel@kbin.social 1 week ago
SpaceNoodle@lemmy.world 1 week ago
Same, but now I’m working on very high-speed stuff for work and starting to get into that hobby-wise as well. Just yesterday had a conversation with a colleague about how things are getting too small to hand-solder.
GluWu@lemm.ee 1 week ago
My dedicated AI machine uses 1866mhz DDR3. Consumers don’t know what they need and will buy whatever the latest new thing is. Smart phones are so dumb. Like wow, your brand new $2500 phone has a benchmark 4x faster than my refurbished $250 phone. Now tell me what you do with all that power. “…well I save 27ms per Instagram post which adds up with how much I use it”. I want to run headfirst into a brick wall.
TimeSquirrel@kbin.social 1 week ago
I meant PCBs. I design custom circuit boards.
Threeme2189@lemmy.world 1 week ago
What is a mil in this context? I’m genuinely curious.
Hawke@lemmy.world 1 week ago
Probably one thousandth of an inch.
user224@lemmy.sdf.org 1 week ago
inch
Ew.
Hawke@lemmy.world 1 week ago
Yes.
kaboom36@ani.social 1 week ago
Hey thousands of an inch are the only part of our imperial system that actually makes sense
Threeme2189@lemmy.world 1 week ago
I’ve heard it referred to as ‘thou’ but not ‘mil’
curiousPJ@lemmy.world 1 week ago
A couple old metrology equipment dated back from the 80s I still use calls them ‘mil’. It’s got dual dials for mil/mm. Gets me confused sometimes because the gauge can go down to couple millionths of an inch/couple nanometers.
LVDT for those curious.
borari@lemmy.dbzer0.com 1 week ago
Yeah, I’ve never heard of that before either. What I have heard of is either MOA or MIL reticles. In that context a Mil stands for milliradian, which is a representation of angle. That definitely doesn’t track with the post though.
SpaceNoodle@lemmy.world 1 week ago
Correct.
flying_gel@lemmy.world 1 week ago
A millimeter i.e a thousands of a meter.
Threeme2189@lemmy.world 1 week ago
5 mm isn’t ‘just over 0.1 mm’. That can’t be right.
AnUnusualRelic@lemmy.world 1 week ago
Well, it depends on your margin of error.
Aceticon@lemmy.world 1 week ago
In the design and manufacture of PCBs (aka circuit boards) a “mil” is a one thousandth of an inch.
flying_gel@lemmy.world 1 week ago
I stand corrected, and I see I didn’t read the comment thoroughly enough either.
Colloquially as a non-pcb maker I would use and hear the term “mill” as short form millimeter so I assumed it was that.
so TIL :)
gregorum@lemm.ee 1 week ago
That inverse square law will fuck you every time
itsmect@monero.town 1 week ago
USB3 is quite forgiving regarding the layout. The standard ±10% impedance matching is fine, and because there is no dedicated clock line you don’t need to do length matching either. Even differential pair length mismatch is not that big of a deal. If 0.1mm is easy to archive, sure go for it, but I’d rather compromise on this in favor of more important parameters.
gregorum@lemm.ee 1 week ago
So, does it just have really advanced error checking? How does it handle the mismatches?
itsmect@monero.town 1 week ago
The signal does not care about how it gets from the sender to the receiver. The only thing that matters is that at the receivers end 0s and 1s can be separated. One common measurement is the eye pattern. If the eye is “open” enough (=matches the spec), communication is possible.
Impedance mismatch causes reflections (visible as oscillation after rising/falling edge), differential pair line mismatch degrades the slop of the signal transition (rising/falling edge). Geometric features only matter if they are large compared to the signal wavelength. As a rule of thumb features smaller then 1/20th can be safely ignored, often times a ratio as large as 1/5 works just fine. USB3 uses 2.5Ghz (5Gbit/s) or 5Ghz (10Gbit/s), where 1/20th result in 3.4mm and 1.7mm respectively (assuming an effective dialectic of 3.17). This is still grossly simplified, because in many real systems you don’t control the entire transmission line (eg. user buys a random cable and expects it to work), so it makes sense that the USB consortium specifies eye patterns and factors in various system uncertainties.
RAM on the other hand uses 16/32/64/128 single ended data lines, with a dedicated clock line. Data does not have to arrive perfectly at the same time, but the margin may be as little as 1/10th of a clock cycle. Here accurate length matching is absolutely required. Its also the reason why the same CPU + RAM combination may archive higher stable clock rates on some mainboards then on others.
gregorum@lemm.ee 1 week ago
Ok, wow. Thank you for educating me on a great deal I didn’t know when I asked the question. And while it does a great deal to bridge that gap… the question remains unanswered: how is this breakthrough achieved?
AnUnusualRelic@lemmy.world 1 week ago
That’s why serial busses won over parallel ones I guess.