PXA270 Random Hangs at Low Core Freq

[marek.vasut@gmail.com (Marek Vasut)]

Dne Po 18. ??jna 2010 19:38:49 Michael Cashwell napsal(a):
> Greetings,
> 
> I've been fighting inexplicable hangs on two different PXA270 designs
> running various kernels since early 2.6.28.x. The first board was custom
> (and of dubious integrity) but I'm currently seeing it on Gumstix Verdex
> PROs running 2.6.35.7.
> 
> At first I thought it was a problem with CPU-freq code itself hitting some
> unaddressed errata but I've eliminated that possibility. The hangs occur
> even if CPU-freq is disabled in the kernel config. All that's required in
> that case is for u-boot to run the kernel at a core frequency of 312MHz or
> lower. If it runs at 416MHz or higher no hangs occur. (With CPU-freq
> enabled the hangs only occur if speeds at or below 312MHz are allowed.
> With those commented out, no hangs.)
> 
> At low core frequencies I can trigger the hang every time by copying a
> several-MB file to a uSD card via the MMC interface. The copy command
> completes but a few seconds later (while the background processes write to
> the card) the CPU hangs.** However, the issue is not specific to uSD/MMC.
> Another developer told me he has seen hangs while receiving data through a
> UART connected via I2C.
> 
> The hangs are hard (rendering JTAG inoperable) and since I have no hardware
> with the Embedded Trace Module exposed I have no way to gather a trace of
> execution up to the freeze.
> 
> I'd like to solve the problem since the lower speeds are more power
> efficient but I'm somewhat stuck regarding how to debug it. I'd like to
> know if it's something I'm doing wrong so my first step is to ask the
> ARM-Linux community if anyone else has run recent kernels on a PXA270
> system at core clock rates of 312MHz or less. (That's also a not so veiled
> plea for someone to perhaps do so if they have the hardware and a few
> spare cycles.)

Could it be memory-related ? Like, RAM crashes because of refresh speed or 
something?

Cheers
> 
> Thanks for any information.
> -Mike
> 
> **: Here's a hang where I'd just started top while background threads were
> writing to the uSD card. top did its first pass and then everything froze.
> (Is the high rate of context switches and interrupts normal?)
> 
> last pid:   389;  load avg:  0.13,  0.05,  0.01;  up 0+00:28:15       
> 12:40:22 27 processes: 1 running, 24 sleeping, 2 uninterruptable
> CPU states:  0.0% user,  0.0% nice, 31.1% system, 13.6% idle, 55.3% iowait
> Kernel: 30832 ctxsw, 16262 intr
> Memory: 32M used, 92M free, 244K buffers, 27M cached
> Swap:
>  This terminal can only display 16 processes
>   PID USERNAME  THR PRI NICE  SIZE   RES   SHR STATE   TIME    CPU COMMAND
>   236 root        1  20    0    0K    0K    0K disk    0:00 28.43% mmcqd
>   389 root        1  20    0 2696K  804K  648K run     0:00  3.92% top
>   378 root        1  20    0    0K    0K    0K disk    0:00  1.96%
> flush-179:0 1 root        1  20    0 2784K  672K  588K sleep   0:00  0.00%
> init 119 root        1  20    0    0K    0K    0K sleep   0:00  0.00%
> rpciod/0 371 root        1  20    0 4208K 1592K 1340K sleep   0:00  0.00%
> sshd 369 root        1  20    0 2788K  716K  632K sleep   0:00  0.00% ash
> 4 root        1  20    0    0K    0K    0K sleep   0:00  0.00% events/0
> 128 root        1  20    0    0K    0K    0K sleep   0:00  0.00% nfsiod
> 251 root        1  20    0 2784K  460K  380K sleep   0:00  0.00% klogd 249
> root        1  20    0 2784K  464K  396K sleep   0:00  0.00% syslogd 5
> root        1  20    0    0K    0K    0K sleep   0:00  0.00% khelper 370
> root        1  20    0 2784K  440K  376K sleep   0:00  0.00% busybox 103
> root        1  20    0    0K    0K    0K sleep   0:00  0.00% kmmcd 2 root 
>       1  20    0    0K    0K    0K sleep   0:00  0.00% kthreadd 3 root    
>    1  20    0    0K    0K    0K sleep   0:00  0.00% ksoftirqd/0
> 
> 
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