Hacker News

69 points by swq115 5 days ago | 24 comments

ysleepy 4 hours ago

I was kinda hoping to get the nitty gritty of how the NIC does the packet matching, how, it wakes up the system via PCIe and how switches route the frames to the port which has/had the client.

Nothing against the article though, but maybe someone knows a good writeup.

jonah-archive 3 hours ago

The original paper proposing the technology is actually very good (and surprisingly still online!): https://www.amd.com/content/dam/amd/en/documents/archived-te...

Animats 3 hours ago

That's more useful. A big question is how much is really turned off in a computer waiting for the wake-up packet. "The power to the Ethernet controller must be maintained at all times, allowing the Ethernet controller to scan all incoming packets for the Magic Packet frame". So the full network controller is still alive. There's not some tiny Magic Packet detector hardware running off a rechargable coin cell or something, with the main power supply turned off. At least not in the original design.

A lot of sleep modes leave more running than you'd expect.

adrian_b 2 hours ago

The Ethernet cards that wait for WoL packets use the "+5 V Standby" supply voltage, which is available on the PCIe slots, coming from the ATX power supplies.

"+5 V Standby" is provided by a separate voltage regulator, which continues to work even when the PC, including the rest of the ATX PSU, is shut down.

"+5 V Standby" typically can provide up to 2 A, i.e. up to 10 watt, though some old PSUs may be able to deliver only up to 5 watt and some of the bigger ATX PSUs may be able to deliver up to 15 watt.

Besides supplying the Ethernet cards, to enable WoL, "+5 V Standby" can be used by the USB ports if configured so in BIOS, to enable waking the PC with the keyboard, or to enable charging from USB even when the PC is shut down.

jonah-archive 59 minutes ago

Exactly this. Many modern PHYs also integrate 802.3az (energy-efficient ethernet, a subset of Green Ethernet) but it's not super common.

I also finally found this old page of using an old dev board to construct a WoL listener for a mobo that didn't support it -- might be an interesting read for the curious: https://web.archive.org/web/20140525022112/https://hackingbe...

> In this script a fifo is created where the output of tcpdump is dumped. For whatever reason tcpdum | grep was not working properly, and would have a “miss” rate of about 50%. So tcpdump output is dumped in the fifo:

> tcpdump -i eth1 2>&1 | tee > /tmp/tcp_wol.fifo &

> and it’s grepped in a loop, when the magic packet (see http://en.wikipedia.org/wiki/Wake-on-LAN) is found , a led is triggered, thus powering-up the computer (with a driver and relay, will come back at this).

pjc50 59 minutes ago

It probably is done in hardware; I expect you'll end up with the TX side of the Mac/phy powered down but all the receive running. Miliamps at most.

elevation 3 hours ago

I was distracted by the poor typesetting in parts of the page. The meaning of the text is overwhelmed by the distracting spacing used to justify the text:

> . I n o t h e r w o r d s , s i l i c o n - o r g a t e - l evel

MrBuddyCasino 2 hours ago

Didn‘t know a whitepaper is allowed to be this readable.

ErroneousBosh 31 minutes ago

Shift registers. It's all done with shift registers.

Terr_ 3 hours ago

Ditto, I clicked and was disappointed.

"How to send a magic packet in $LANG" isn't very interesting to me. There are plenty of guides for it, and I remember actually doing it 20+ years ago with a short PHP script.

Even at the time, the task didn't seem like "enough" for a show-the-world blog post. A dramatically shortened version (no validation, error handling, logging, etc.) for your amusement:

    // Given $macAddress and $addr and $port
    $macAddress = str_replace(":","",$macAddress);
    $macAddress = str_replace("-","",$macAddress);

    $header = pack('H12','FFFFFFFFFFFF');
    $payload = pack("H12",$macAddress);
    $packet = $header . str_repeat($payload,16);

    $sock = socket_create(AF_INET, SOCK_DGRAM, SOL_UDP);
    socket_set_option($sock, 1, 6, TRUE);
    socket_sendto($sock, $payload, strlen($payload), 0, $addr, $port);
    socket_close($sock);

arscan 2 hours ago

To perhaps give a little insight into why this is on the front page by someone who upvoted it: I didn't realize it was so open and easy. Now I do. The Golang code simply serves as proof in how open and easy it is.

> Even at the time, the task didn't seem like "enough" for a show-the-world blog post.

Its an old (de facto industry) standard, but maybe more relevant than ever. I'm interested in moving more of my compute usage off-cloud these days, which is why this is of interest to me right now. I suspect many others feel the same way.

Might be a good time to post other tidbits of knowledge you have like this, targeted at software engineers that are starting to get more into infrastructure management. Standards that are ubiquitous and just work are awesome.

ryandrake 4 hours ago

[2020] and wow, what a title. It looks like someone was trying to decide between "How Wake-On-LAN works" and "How does Wake-On-LAN work" and "How do Wake-On-LANs work" and just picked a random combination of words from those choices.

Aurornis 4 hours ago

English is not the author's primary language.

I think they did a great job for writing in a secondary language.

yyhhsj0521 3 hours ago

They did a much better job than a JavaScript developer writing Java.

Sarkie 46 minutes ago

Don't be Reddit

ErroneousBosh 32 minutes ago

He's Norwegian and studied in Wales.

How good are you at blogging in your third language?

Ich? Nicht so gut, aber Ich kann veillicht ein bisschen posten auf Deutsch.

Agus co dhiù, bha Beurla an dàrnan cànan agamsa.

So if my posts in English (proper English, not North American "Simplified English") are a bit squint at times, blame that.

wat10000 3 hours ago

This sort of thing is quite common for non-native speakers. The fact that you can say "how does X work" and "how X works" but not "how does X works" is not particularly obvious, and easy to mix up.

chungy 4 hours ago

Somehow, the bad grammar gives something special by signifying an LLM didn't write it.

Then again, an LLM could probably help clean up the grammar.

michaelbuckbee 4 hours ago

This is one of those slippery slope things where Grammarly did "just" Grammar and then slowly got into tone and perception and brand voice suggestions and now seems to more or less just want to shave everything down to be as bland as possible.

jerf 2 hours ago

All you have to do is prompt your AI with a writing sample. I generally give it something I wrote from my blog. It still doesn't write like I do and it seems to take more than that to get rid of the emdashes, but it at least kicks it out of "default LLM" and is generally an improvement.

ErroneousBosh 21 minutes ago

I tried using an LLM to help me write some stuff and it simply didn't sound like I'd written it - or, it did but in a kind of otherworldly way.

The only way I can describe it is like when I was playing with LPC10 codecs (the 2400bps codec used in Speak'n'Spells, and other such 80s talking things). It didn't sound like me, it sounded like a Speak'n'Spell with my accent, if that makes sense.

No? Okay, if not, if you want I could probably record another clip to show you.

jayd16 4 hours ago

I'm sure we'll start to get 'authentic' bad grammar LLMs that actually mussy up your grammar for that natural feeling.

dyauspitr 4 hours ago

You can do that now. Just ask it to use bad grammar and introduce spelling mistakes and it does.

havblue 4 hours ago

Maybe you should run it through ai to correct the grammar before reading it...