DRAM Defect in Some Palm, TRGpro, and Visor Models
Palm is making available a software patch to address a faulty 8MB DRAM component identified in a limited run of Palm IIIc, IIIxe, and Vx products manufactured between the period of October 1999 through May 2000. Palm uses multiple sources for these DRAMs in the manufacturing process. One of the suppliers of DRAM components provided Palm with a faulty component that can cause random data to be written on the Palm device. If a unit is determined to have the faulty chip, the software patch will provide a complete fix.
A majority of Palm handhelds are free of the defect, including all 2MB, 4MB and most 8MB units.
TRG is also acknowledging that some of their units are also affected by the defect and suggests that all users affected upgrade to Palm OS 3.5.1, which is free. If you don't want to upgrade, TRG will soon be offering a patch for OS 3.3.
And now Visor has stepped forward to state that they, too, are affected. The majority of Visor handhelds are free of the 8MB DRAM issue, including all 2MB Visor Solo and most 8MB Visor Deluxe units. Only a limited number of Visor Deluxe handhelds shipped between the period of January 2000 to June 2000 may be affected with this faulty chip. Visor is offering a test app to look for the defect but currently just suggests you contact tech support if you discover your Visor is affected.
TRG is offering the following technical description of the problem:
Q: What causes the DRAM problem?
A: The exiting of self-refresh mode on a certain vendor's DRAM was not implemented correctly. This can cause a portion of memory to become corrupted.
Details: The Palm OS goes to sleep and wakes up once every minute to perform some housekeeping functions. This, in turn, causes the DRAM to enter and exit self-refresh mode once per minute. Since self-refresh mode is flawed in certain vendor's DRAMs, there is a chance for data corruption to occur every time self-refresh mode is exited on units which use that vendor's DRAMs.
Q: What is DRAM self-refresh mode?
A: When your unit is on, the processor is responsible for maintaining the contents of DRAM. When the unit is "off", the processor is shut down and the DRAM is commanded to assume responsibility for its own refresh. This mode is called DRAM self-refresh.
Q: How likely is the failure to occur?
A: If your unit contains the faulty DRAM, it is a statistical certainty given infinite time.
Details: Through testing, TRG has observed that there is about a 1/8000 chance of a row of data (2K) being corrupted every time self-refresh is exited. In a 24 hour period, the TRGpro will wake up 1440 times. In 5.5 days, the unit will experience 8000 wake / sleep cycles. If a corruption occurs in an area of memory that is in use, you will experience the problem. Since the location of the failure in memory is random, your odds of detecting the failure will increase with the amount of memory you use.
Q: How can software fix this problem?
A: TRG developed a work-around which does not put the DRAM into self-refresh mode. If self-refresh mode is not used, the problem will not occur.
Details: TRG refreshes the DRAM using a technique called "burst CBR refresh". This avoids the need to enter/exit self-refresh mode.
Q: How did TRG discover this problem?
A: TRG was testing a change to Palm OS3.5 that required the unit to wake up once every 5 seconds instead of once per minute. This increased the chances of the failure occurring by 12x. With the help of TRG's beta testers, the problem was then detected and isolated to a particular vendor's DRAM. TRG then reported the problem to the DRAM manufacturer and developed the fix.
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