Wednesday, June 26, 2013

Making the AR9330 SoC wifi, or "how it feels doing things right.."

Well, "doing it right" is subjective. Sure. I'll grant you that.

I brought up the AR9330/AR9331 SoC support a couple of months ago. Unfortunately the Atheros reference board (AP121) comes with 16MB of RAM and 4MB of flash - which is just painful to do FreeBSD-HEAD development in.

Yes, I know. 16MB of RAM is tons of space... for FreeBSD-4. Anyway. That is a rant for another day.

So I managed to bring up the basic SoC support (which took longer than I thought - I had to learn how to write a FreeBSD uart driver!) but I decided to put wifi on hold until I found a board with more RAM and flash.

Along comes the Carabola 2 from 8devices.com. (http://8devices.com/carabola-2) . It's an AR9330, but with 64MB RAM, 16MB flash and a full-featured uboot. This is perfect for .. well, anything. And it's 30 Euros in quantities of one. Wait, it's cheap, it's fully-featured and it's available online? No way. What's the catch?

The catch - it wasn't running FreeBSD.

So I finally decided to bring up wifi support on FreeBSD.

The AR9300 HAL from Qualcomm Atheros includes the AR9330/AR9331 SoC wifi support. So I had to make it compile and make it work. How hard could it be?

Firstly - I wasn't compiling it in by default as it's only really useful for the SoC and not for normal PCIe NIC support. So, I needed to add that in. Luckily, I had to set AH_SUPPORT_HORNET into the source. Cool.

Next - the bus glue. The SoC internal bus isn't PCIe, it's what they call AHB, or "Atheros Host Bus." It's a derivative of a standard on-chip peripheral interconnect bus. The FreeBSD ath_ahb driver only supported AR9130, so I had to extend it to support non-AR9130 devices. That got it probing and attaching, but it wasn't finding the calibration / configuration space.

Next - gluing in the calibration data. It's on-board in the system flash, rather than on-chip (OTP) or an external EEPROM. The EEPROM space is 16KiB in size, rather than the 4KiB space used by the AR9xxx series SoCs. Also, the AR9300 HAL already seeks into the EEPROM space to grab the data at offset 0x1000, so I don't have to do that like I do with the AR9130 and related chips.

Finally - I had to teach ar9300_attach() that it needed to copy the EEPROM data I was giving it from ath_ahb into the copy it uses when setting things up.

And... that was it. After that, it booted and came up correctly. I was shocked.

You can find the boot log and dmesg at https://code.google.com/p/freebsd-wifi-build/wiki/Carambola2 .

I haven't yet tested 802.11s (mesh) on this stuff, nor have I made TDMA work with this series of chips. But it's my eventual goal to make this board one of the "gold standard" boards for people wishing to enable their projects with wifi mesh. I bet it'll work out of the box as it stands, so if you're up for a bit of tinkering, buy a handful and set it up!

Enjoy! It's the best 30 euro you'll spend!

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