Date: Thu, 31 Oct 2019 16:05:33 -0400 From: Austin Shafer <ashafer@badland.io> To: Farhan Khan <farhan@farhan.codes> Cc: freebsd-wireless@freebsd.org Subject: Re: Best way to explore the 802.11 rtwn source code? Message-ID: <512B62A4-CCB7-4C05-A988-0E19443A2DD0@badland.io> In-Reply-To: <d3705517-ae52-4644-883d-6e65d327e93d@www.fastmail.com> References: <1F9F7008-59C4-42DF-AF1E-0028BD9576F5@badland.io> <d3705517-ae52-4644-883d-6e65d327e93d@www.fastmail.com>
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Hi Farhan,
Thanks for the reply!
> rtwn is a bit more complicated than other drivers. Any rtwn device will
> require at least three drivers: The PCI or USB driver, the general rtwn
> driver which contains shared code, and the device-specific driver. While
> I'm sure you can follow the code, I would suggest starting with something
> a bit simpler. I learned the hard way :)
Yep I’ve noticed that pattern in other drivers, particularly the i2c
hid driver I messed around with. What's a good example of a "simple"
driver?
> One good approach would be to take a simple driver, look at its ieee802com
> object, and see what avenues the ieee80211 stack has to interact with the driver.
> I would learn about the powering on process, setting up DMA, initializing the interrupt
> code, and seeing how interrupts are handled. From there I would look into Rx, Tx
> and then the rest of it.
Following through the rtwn_attach function I agree that following the
ieee80211com object is a good idea. If anyone else finds this useful
the r21au_attach function is also informative as it adds the interface
methods to the softc. The man pages are great as usual.
Is ieee80211_ifattach a good point to start reading? It seems to kick
off a cascade of *_attach methods which is a little tricky to keep
track of.
Reading all this does make me realize there are many 802.11 features I
don't know about, so if you have a good 802.11 reference I'd love to
hear it.
> Please let me know if this helps. Also, if you have any more specific
> questions, please let us know. What are your objectives?
My adapter has frequent times when it will have crippling packet loss
(40% to 100%) for 5 ish minutes until things all of a sudden return to
normal. I'd love to be able to figure out what's actually going wrong.
Also I'd enjoy some 802.11ac support, so if there is any grunt work
which a newbie can help with I am glad to chip in.
> I was writing an introduction on this very topic, but $LIFE and other
> projects got in the way. Maybe I should get back into it?
I'm not sure about others, but I would definitely read it.
Thanks!
Austin
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