no prints from early printk

Hi Gangadhar,

I think you should also append "earlyprintk" to the kernel bootargs. Did you try this?

Best regards,
Miroslav

Hi Miroslav,

                     I've tried with this earlyprintk=ttyO0, 115200, keep. Kernel hangs if i pass this in bootargs without any prints.

Regards,

Gangadhar

Try only "earlyprintk" appended to the end of the bootargs. Example:

setenv bootargs ${bootargs} earlyprintk

Best regards,
Miroslav

Hi Miroslav,

I've tried even this - only "earlyprintk". Kernel hangs without any prints.

I've also tried using printascii() in vprintk_emit() of kernel/printk/printk.c suggested in one of discussion forums. Same response, no prints, kernel hangs.

Regards,

Gangadhar

Can you please let me know which SDK is this - v6 or v7? I'd like to try it myself when I have the time.

Best regards,
Miroslav

Hi Miroslav,

                      SDK 7.0.

Regards,

Gangadhar

Gangadhar,

I think the correct debug UART port should be DEBUG_AM33XXUART1.

I just tried this using SDK v7 with the following configuration options enabled and the system boots without any hangs:

CONFIG_DEBUG_LL=y
CONFIG_DEBUG_AM33XXUART1=y
CONFIG_DEBUG_OMAP2PLUS_UART=y
CONFIG_EARLY_PRINTK=y

Best regards,
Miroslav

Hi Miroslav,

                      This was missing - CONFIG_DEBUG_AM33XXUART1=y. I enabled it. I connected to UART1 on daugter board but still no early_printk() prints.

Regards,

Gangadhar

It should be noted that early_printk does not print anything to the UART until the UART is initialized.

The printout is just stored in the memory, and after the UART is operable, all the data is sent there.

If kernel hangs before the UART can accept the data then you would not get anything actually printed.

In such a hard cases JTAG could be used for debugging, or LED toggling - anything providing visible result right away, without memory buffering.

Hi sviss,

              I'm trying early_printk() on AM335x EVM. There is no problem with kernel. The only thing is I don't get prints from early_printk(). Finally I'll use this on my custom board for debugging.

One more thing what is the baudrate of UART1(placed on daughter board) on which early_printk() output is available.

I've set my minicom to 115200.

Regards,

Gangadhar

Right, this is what I suggested. If you tried everything and it still does not work (or if kernel hangs as you noted too), you should put something inside the early_printk handler, or near it, to see if your execution actually comes there.

Gangadhar,

The baudrate is 115200 for all UART ports by default. It is defined inside <u-boot>/include/configs/am335x_evm.h:

#define CONFIG_BAUDRATE        115200

and it is used inside the early system init function init_s() in <u-boot>/board/ti/am335x/board.c.

Best regards,
Miroslav