MakeLinux.com managed to boot Linux from the bootloader to console within 300ms using a customized (and minimal) version of Linux running on Beagleboard based on TI OMAP 3530 (Cortex A8) as per of their Super Fast Boot project.
Here’s the analysis of the boot sequence and timings:
• Logging starts at 70 ms from reset. Boot time from reset is 300 + 70 = 370 ms.
• Logging starts at 330 ms from power on. Cold boot time is 330 + 300 = 630 ms.
• Loading of 1.5 MiB Linux image from NAND takes 237 ms with throughput 6 MiB/s.
• Code execution takes 60 ms or 43M CPU cycles. (For other CPU frequency execution time is different, but number of processor cycles is the same)
• The most time consuming operation is coping firmware from NAND flash.
They used a Linux 2.6.32 kernel from DVSDK 3.01, in a minimal configuration (900KB footprint), the boot loader comprises an optimized x-loader, without U-boot and the only application in the rootfs is a statically compiled BusyBox v1.16.2 humble shell (600KB footprint) for a total of 1.5MB.
Bear in mind that is is a minimal kernel, so you’d probably not be able to do much with it as it only runs busybox.
For further details ad if you’d like to get the binary image, please visit http://www.makelinux.com/emb/fastboot/omap