Johnny Hung wrote: > Hi All: > I have a powerpc arch platform. The default console is ttyS1 not > ttyS0 in the platform. My question is how the kernel print debug > message > like DBG before parse kernel command line and do console_setup > function. The command line passed to kernel about console info is > console=ttyS1. > So kernel can not print anything before parse cmd line and initial > console but the result is against. Anyone point me or give me a clue > is appreciate. Before the console is set up, the printk data is formatted and put into the kernel log buffer, but not sent to any console. Any messages printk'ed before that are buffered but do not appear. When the console is initialized, then all buffered messages are sent to the console, and subsequent printks cause the message to go to the log buffer, but then immediately get sent from there to the console. Under certain conditions you can examine the log buffer of a kernel that failed to initialize it's console, after a warm reset of the machine, using the firmware memory dump command. See http://elinux.org/Kernel_Debugging_Tips#Accessing_the_printk_buffer_after_a_silent_hang_on_boot for some tips on accessing the log buffer of a previous boot. Note also, that if the serial console does not come up, but the kernel successfully boots, and you can get a network login on the machine, you can always print out the kernel log buffer messages using 'dmesg' at a user-space shell prompt. Hope this helps! -- Tim ============================= Tim Bird Architecture Group Chair, CE Linux Forum Senior Staff Engineer, Sony Corporation of America ============================= -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
