daalex

> I wondered why a custom kernel came so late. If you want to optimize, wouldn't you start with LFS or some source-based distribution? Autonomous software updates don't seem to be a necessity anyway on such a device.

Buildroot (which they used) is made exactly for this. With buildroot, you configure your own "Distribution" and generate a single bootable image from it.

> In addition, I wonder if it would be possible to optimize the EFI/BIOS on such a device. At least on my standard Arch Linux desktop, it takes a significant amount of boot time:

Not exactly sure about raspberry pi hardware, but a lot of other embedded SoCs have a pretty minimal bootloader that runs with u-boot, which is typically very fast (at least if you set the delay it waits for user input to 0)

> In one of my computer engineering classes, I learned that power consumption rises as the square of clock frequency - so doubling the clock will quadruple the power.

This is not quite correct. Switching power of a chip (ignoring static leakage) is proportional to voltage squared times frequency. Most chips require a higher voltage to reach higher clock speeds, so there is a quadratic relationship there. However, I believe that the raspberry pi does not have dynamic voltage control, so reducing clock speed without also reducing voltage will not effect total switching energy consumption.