Comment by alex43578
1 day ago
I get that to properly test a cable, you need that level of accuracy, but for home use, couldn’t you get away with a source and a receiver that are far cheaper?
If a USB4 device can output a USB4 stream and the receiver can check that stream for errors, isn’t that sufficient?
At some point you end up testing the peripheral and/or host rather than the cable. For example, cables often state that they can handle up to 240W ... but no 240W USB-PD chip has ever gone into production -- you won't even find one at the hottest USB-PD trade shows[0] in China.
It could be reasonable for computers to be allowed to trigger a data throughput test and the peripheral would state "I support up to 40Gbps of receiving/sending", and then send a simple pattern that can be generated on the fly. But a lot of devices can't receive/send that 80Gbps of data for long enough to perform a decent test - the storage, RAM, buffers, etc get depleted or act as bottlenecks.
If you know enough to accurately interpret the measurements you get from that, you know enough to write your own computer program to try to send 80Gbps from one computer to another and use DMA to process it in real-time without hitting storage (which a lot of peripherals likely don't have the CPU to accomplish).
If you don't know enough to write those test applications, you probably don't know enough to interpret the results of a built-in test function and the measurements would confuse and frustrate a lot of well-meaning, nerdy, but under-educated consumers who make assumptions about why they're not actually getting the rated speed.
Idk, my opinion doesn't go one way or the other here. Perhaps I myself don't quite know enough to be a good judge of that concept.
0: https://asiachargingexpo.com
> For example, cables often state that they can handle up to 240W ... but no 240W USB-PD chip has ever gone into production -- you won't even find one at the hottest USB-PD trade shows[0] in China.
Your information is out of date. You can buy 240W chargers from Framework which I assume are just rebranded Delta chargers:
https://frame.work/products/power-adapter-240w
The Framework 16 supports this 240W charging input, as well.
I think you’re overthinking the bottleneck side of things: RAM to RAM would be sufficient to capture if the cable is capable of 40Gbps.
All an end user cares about is if the cable is the bottleneck, if you think you have known-good devices. If I have a MacBook and a good NVMe enclosure, I want to know if my cable is fast enough, rather than have it quietly fall back to 3.2 or worse.
You don't need to test at 240W. You primarily need to test that it can handle 5 amps with limited voltage drop. You can also test that it handles 48 volts but basically any cable can handle 48 volts. The chance that either one of those very mild operating conditions compromises the other when you combine them is minimal.
>no 240W USB-PD chip has ever gone into production
This is because the cross-sectional-area of the conductor would create an inflexible cable – and even then the connector (even though rated) could never handle a sustained 240W in the real world.
Fires. Fires everywhere... this is why no 240W chip exists.
src: electrician
240W for USB-PD is only 5 Amps (USB spec only calls out for 240W at 48V) which can be safely carried by a standard 16AWG conductor.
USB-IF certifies plenty of USB cables as being tested safe for 240W. The reason 240W chargers don't exist is due to cost and a chicken-and-egg problem. There’s not really any demand for it.
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Plenty of USB-C cables are capable of charging at 5 amps continuously and do so today. How is the voltage relevant to how much power is dissipated in the cable? That’s the only difference between a 100W charger and a 240W charger.