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Software Over-Optimization
Apr 27, 2011
The same user who found and solved the LM386 problem had another question since last year. He bought an ET6602 IP phone for 50RMB on Taobao, but found the phone can only use PA168T software 1.51, with 1.64 the phone got very unsteady. I thought it was just another non-standard PA1688 device which can not work with standard software at that time. But now the user's enthusiasm in technology and ability to solve problem impressed me, and I decided to check the problem again.
To my surprise, this ET6602 indeed can work with our standard 1.51 software, which was the first software release since Centrality discontinued PA1688 business in 2006. But with current 1.66 software release it often got dead. Then I tested 1.57 failed, 1.54 ok, 1.56 ok. After comparing the source code between 1.56 and 1.57, it was clear that the software optimization for RTL8019AS caused the unsteady problem.
I can still remember those changes, which was first made on AR1688 performance improvement, and then moved back to PA1688 without widely tests on various PA1688 devices. Obviously not all PA1688 devices are created equal, this ET6602 is poorly made in hardware and needs special software error protection. After restored those software over-optimization, I updated its 1.67 test software in our website.
PA1688 based ET6602 IP phone PCB

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