Android, Beagleboard, Kernel and the DSP-Bridge
Application access to the DSP
The Beagleboard features a Digital Signal Processor (TMS320C64x+ DSP). For our spectrum analyzer it would be a very nice feature to calculate the FFT in the DSP.
To access the DSP the Kernel needs to implement the DSP-Bridge driver. However, it is quite challenging to get the driver into the Kernel. Several attempts to patch the Embinux Kernel with the original patches failed. [Embinux Kernel Git Repository]
The good news is that the omap-kernel (linked in the Android Git repository) features the DSP-Bridge driver that we were looking for. [Android omap Kernel Git Repository]
The challenge was to get the Kernel running on the Beagleboard. We had first given up on it since the USB-Host Controller was not working. But after trying every other Kernel (Embinux, 0xdroid, mainline omap kernel, etc.) we gave it another try. Since we are booting an NFS Root File System we needed USB and Ethernet support on startup time. The key is to configure the Beagleboard’s USB-OTG as a Host Device. This can be done in the menuconfig of the Kernel. This was not the only challenge. A Kernel panic occurred when looking for the init file.
The solution was to configure the Kernel properly and including all Android driver modules (which seems kind of obvious at this point). To give you an idea of how the config of the 2.6.29 Android Omap Kernel could look like you can check our .config out here. [.config file]
Android now boots correctly.
Well, there is still one problem though. The Input Event Subsystem seems to be messed up, thus our keyboard and mouse is not working at all.
The Event Input Subsystem works now properly with the above .config file.
To break it down:
Working with the omap-Kernel of the Google Git repositories we can state the following:
Pro:
- DSP-Bridge Driver
- Nicely maintained by a big community
Con:
- USB-Host Controller not working yet (USB OTG in host mode works)