最近在调一批新板,遇到这这样的问题:am335x的板子,启动Linux后挂上文件系统,过一段时间系统时间会自己改变,这个现象发生的还比较频繁,每次改变的时间也不一样。每次进系统我都用date命令设置了系统时间,并且用hwclock -w同步rtc的时间,但是过一段时间系统时间就变了,然而rtc的时间却没有改变。请问下这是什么原因啊??之前一批板都没有这个问题。
Steven Liu1:
这个问题这两天经常遇到,http://www.deyisupport.com/question_answer/dsp_arm/sitara_arm/f/25/t/122428.aspx
这个是你的同事吗?
建议是一样的,建议你们先检查一下硬件设计,在AM335x的errata上面已经提到过这种因为噪声问题而引入的时间错误情况。
Advisory 1.0.30 OSC0 and OSC1: Noise Immunity Improved When Crystal Circuit is ConnectedDirectly to PCB Digital GroundRevisions Affected 2.1, 2.0, 1.0Details The Sitara AM335x ARM Cortex-A8 Microprocessors (MPUs) data manual (literaturenumber SPRS717), revision F and earlier, has specified OSC0 crystal circuit groundsonly be connected to VSS_OSC in both ZCE and ZCZ packages, and OSC1 crystalcircuit grounds only be connected to VSS_RTC in the ZCZ package. The VSS_OSC andVSS_RTC terminals are connected to the VSS terminals inside the AM335x device,which connects the crystal circuit to the PCB digital ground, but this ground connection isa higher impedance connection than a direct connection to the PCB digital ground.The higher impedance connection through the AM335x device to the PCB digital groundmakes it easier for electrical noise to couple into the crystal circuit. If the noise is largeenough, it is possible that the oscillator output may produce clock glitches to variousinternal logic circuits. These clock glitches may cause unexpected behavior.Workarounds Connect the VSS_OSC and VSS_RTC terminals and respective crystal circuitcomponent grounds directly to the nearest PCB digital ground, making it more difficult fornoise to couple into the crystal circuit.
joker777:
回复 Steven Liu1:
谢谢你的回答!!~这个不是我同事,但是他的问题和我的一样,我这也是过一段时间就变快30个小时左右,我找硬件的同事确认过说是连着地了,另外我们的用的是ti-sdk-am335x-evm-05.07.00.00。我再确认下硬件这里先。
joker777:
回复 Steven Liu1:
而且之前我们做的板子都没有这个问题,但是这一批做的板子基本上都会出现这个问题。硬件没做有这方面的改动。