#U boot console how to#

One of the primary purposes of those scripts is to construct a proper set of bootargs for the user-space being booted.

In lots of previous posts, we’ve described the anatomy and particulars of boot scripts. In general, you won’t need to know about atags, but if you mess around at all with U-Boot, you’re likely to know a lot about bootargs. The short answer to that question is U-Boot, but the more precise answer is that the U-Boot boot loader passes the kernel command-line transparently to the Linux kernel using a feature known as atags from a U-Boot variable named bootargs. I’ll walk through a number of them below, but first I’d like to talk about how and where these variables are set and handed off to the kernel. The last four lines above show a rather complicated set of flags and variable assignments used in a boot of Android on the Nitrogen6X board. Kernel command line: console=ttymxc1,115200 init=/init rw no_console_suspendĪnsole=ttymxc1 vmalloc=400M fbmem=28M,10M,10M calibration tsdev=tsc2004 PERCPU: Embedded 7 pages/cpu s5760 r8192 d14720 u32768īuilt 1 zonelists in Zone order, mobility grouping on. Memory policy: ECC disabled, Data cache writealloc Machine: Freescale i.MX 6Quad Sabre-Lite Board Linux version 3.0.15-ga753097 (gcc version 4.4.3 (GCC) ).ĬPU: ARMv7 Processor revision 10 (ARMv7), cr=10c53c7dĬPU: VIPT nonaliasing data cache, VIPT aliasing instruction cache The next time you boot Linux, I encourage you to pay attention to the start of the kernel’s output to the serial port:

#U boot console how to#

When combined with a U-Boot variable named bootargs, this feature allows you to tell the kernel how to configure various device drivers, where to find the root filesystem and can even be used to pass information to applications on the system. The Linux kernel has a lot of features that can be controlled at boot time through a feature known as the “Kernel command line”.