Problem with Busybox shell

MohanReddy koppula mohanreddykv at
Wed Jan 19 23:06:24 EST 2011

I further debugged and found that flush_to_ldisc() function is not
called which actually wakes up the readers. This is a worker function
and is not being scheduled. I suspected whether timer interrupts are
generated or not. powerpc uses decrementer exceptions as timer
interrupts. I see that timer_interrupt() function in
arch/powerpc/kernel/time.c is not called at all. I printed even
jiffies values and it is not incremented. And I beleivethis makes
scheduler is not scheduling this worker thread.

 I think if flush_to_ldisc is not called nothing can be read from the tty.

Please let me know what could be the reason for timer interrupt being
not called.


On Wed, Jan 19, 2011 at 12:37 AM, tiejun.chen <tiejun.chen at> wrote:
> MohanReddy koppula wrote:
>> But, if there is any problem with cable I could not have seen any
>> character in the interrupt routine of the driver. I turned off both
> I suppose the bootloader, i.e u-boot, works well so looks this should not be
> issued by the cable at least.
>> software and hardware flow control as by board doesn't have hardware
>> flow control. tty_read is called and it hangs at ldisc->read. And I
> Any panic information? Or any dead lock? Which line in detail?
>> see that data is put into the tty buffer by the driver. Will there be
>> any problem with copy_to_user() if there is some problem in the
>> memory?
> Can the serial driver support the poll mode? If so maybe you can take a try to
> exclude any interrupt reason.
> And even you can remove all codes to initialize the corresponding PIN & CLK
> dedicated to the serial port, then try again since the bootloader already did this.
> Tiejun
>> Thanks,
>> Mohan
>> On Tue, Jan 18, 2011 at 12:55 PM, Nicholas Mc Guire <der.herr at> wrote:
>>> On Tue, 18 Jan 2011, MohanReddy koppula wrote:
>>>> Hi All,
>>>> I am working on an MPC885 based custom board. I am able to boot up the
>>>> linux (linux- I could see busybox shell (ash) prompt. But it
>>>> is not accepting any inputs, I am not able to enter any command, it
>>>> just hangs there. I am using ttyCPM0 terminal.
>>>> I suspected if there was any problem in CPM driver interrupts
>>>> generation and put some printk's in the interrupt handler and could
>>>> see interrupts are raised and data is read, but shell is not taking
>>>> the input.
>>>> I wrote an init.c and opened the ttyCPM0 and tried to read from it,
>>>> but couldn't. I am able to write to ttyCPM0 and see it on the host
>>>> minicom.
>>> if you are using minicom to connect check if you have hardware/software flow
>>> control turned on - it also could be a cabling problem - had this with the
>>> beagle board where the tx line was on the wrong pin - so I got output but
>>> could not get any response to input.
>>> hofrat
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