Using Qemu and Chroot to replace your cross-compile toolchain
Awhile back I wrote about how you can set up a cross-compile toolchain for compiling on x86_64 with the Raspberry Pi as a target. There is another, perhaps easier way to do the same thing by using Qemu 2.0 as your backend.
By installing and enabling Qemu support, you can run code compiled for another architecture (that is supported by Qemu) on your native machine. You can then create a Chroot environment, perhaps similar to what you have on your Raspberry Pi, and run it as if it was natively.
Cross-compiling for Raspberry Pi on Ubuntu
While the Raspberry Pi 2 has four cores to churn through code, it still takes longer to compile than on most workstations and laptops. If you are feeling adventurous, you can try cross-compiling which has become easier to set up and get working.
Cross-compiling is when binaries created are for another target architecture than the one you are compiling on. This kind of set up is very typical when creating Android applications. The end result is that you can take the resulting binary and place on its target platform, and it will run there.
There are even tricks to getting the cross-compiled binary to also run on your native system!
In this guide, I’ll walk you through:
- Setting up a cross-compile toolchain in Ubuntu (15.04 Vivid)
- Setting up the proper exports
- Compiling a test program for your native and target armhf platform
- Compiling the latest Raspberry Pi 2 kernel with VC4 support.
VideocoreIV Glamor on your Raspberry Pi
Running an X (Xorg) server on your Raspberry Pi is frustrating. You can either use the fbdev or fbturbo driver which will give an un-accelerated 2D environment with swrast 3D (OpenGL) all beating your poor RPi’s CPU. Overclocking it will only help you so much which is a pity considering that there is another layer on the SoC that would be perfect for that but is now unused.
Enter the VideocoreIV (VC4) and Eric Anholt (formally of Intel, now of Broadcom), who are going to breath new life into the RPi. The idea is to offload the 2D rendering, via Glamor, to the VC4 with OpenGL calls. Since a OpenGL stack needs to exist, that means there will be a Direct Rendering Manager (DRM) Linux kernel module and Gallium/DRI module in Mesa.
This is happening now, here is the current status of support via the Piglit test-suite: skip 19102, fail 3866, pass 3146, crash 153, total 26267
Development on the Raspberry Pi
Now that I’m a proud owner of a Raspberry Pi, I’ve being really stressing the little guy. There is only but so much a ARMv6 processor, on an microSD with only 512MiB of ram can do, which means that compiling on such a machine is going to take a really long time.
Take for example OpenMW, currently it takes about 4 minutes on a quad-core i7 to compile. You’re in for a treat on the Pi, it will take you at least a day, two days if you realize that half-way through the OOM Killer came through and killed your cc process. This is about the time you start wondering about various ways to improve the situation, such as a larger swap file or using zram.
At this point, I was wondering about other ways compiling binaries and packages for the Pi. There was cross-compiling, but then I would have to set up a full toolchain and recompile all the packages from scratch. That will have to be for another post though as it is another world. Another option is to try virtualizing the Pi and apparently QEMU gets us pretty darn close.
Wireless BCM4312 with the 3.10, 3.11, 3.12 and 3.13 kernels
The hybrid driver from Broadcom was updated again in September (2013) with all the previous patches and a few other fixes as well. This brings them up to support linux kernel 3.9, which is very much welcome.
Sadly it breaks again with >= 3.10 with many warnings and errors which isn’t good considering that Ubuntu (13.10) Saucy Salamander is about to be released.
We do have a patch for you though that gets us working again up to the 3.11 kernel.
Chipsets supported by “Broadcom’s IEEE 802.11a/b/g/n hybrid Linux® device driver” are: BCM4311, BCM4312, BCM4313, BCM4321, BCM4322, BCM43224, BCM43225, BCM43227 and BCM43228.
