question: Why the nand_wait() wait for 20ms for nand program.

[Matthieu CASTET]

Huang Shijie a écrit :
> 于 2013年01月21日 17:15, Matthieu CASTET 写道:
>> Huang Shijie a écrit :
>>>   于 2013年01月21日 16:57, Matthieu CASTET 写道:
>>>> Huang Shijie a écrit :
>>>>> 于 2013年01月18日 20:26, Matthieu CASTET 写道:
>>>>>> Huang Shijie a écrit :
>>>>>>> Hi all:
>>>>>>> Why the nand_wait() wait for 20ms for nand program. could we
>>>>>>> expand this time to 40ms? I have a nand chip : Micron MT29F64G08CBABAWP.
>>>>>>> The chip's BUSY/READY pin may needs more then 20ms to become ready,
>>>>>>> though its
>>>>>>> datasheet tells me the tPROG's max value is 2.5ms.
>>>>>>>
>>>>>> Don't you have an hardware problem (missing pullup/down on ready busy pin) ?
>>>>>>
>>>>>> If the datasheet say the max value is 2.5 ms , how it can be more than 20 ms.
>>>>> I finally found the root cause.
>>>>>
>>>>> I added the do_gettimeofday() in the nand_wait() to measure the
>>>>> READY/BUSY time. The code is like this:
>>>>> ---------------------------------------------------- code start
>>>>>
>>>> Could you dump jiffies and timeo in your code ?
>>> The following just shows some part of the log:
>>>
>>> [my_nand_wait]status : 80,<21480, 21480>,<  665911, 664170>,<1, 1741>
>>> [my_nand_wait]status : 80,<21480, 21480>,<  735989, 734626>,<1, 1363>
>>> [my_nand_wait]status : 80,<21480, 21480>,<  805693, 804825>,<0, 868>
>>>
>>>  From the log, we can see that the kernel just waits for 1741us to break
>>> the while loop,
>>> not 20ms.
>>>
>> Yes but you should display jiffies and timeo value to understand why the kernel
>> thinks 2 jiffies elapsed.
> I dumpped the jiffies and timeo too. The jiffies is really _equal_ to 
> the timeo, and then the while loop breaks.
> 
> thanks for your comments.
> 
> I think there is something wrong with the timer.
> 
timeo += (HZ * 20) / 1000;

So what is the value of HZ ?

In order (HZ * 20) / 1000 is 0 HZ should be < 50.


Matthieu