100 lines
3.1 KiB
Text
100 lines
3.1 KiB
Text
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USB NKRO MEMO
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=============
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2010/12/07
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References
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USB - boot mode, NKRO, compatibility, etc...
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http://geekhack.org/showthread.php?t=13162
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NKey Rollover - Overview, Testing Methodology, and Results
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http://geekhack.org/showwiki.php?title=NKey+Rollover+-+Overview+Testing+Methodology+and+Results
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Terminogy
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---------
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NKRO
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ghost
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matrix
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mechanical with diodes
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membrane
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OS Support Status
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-----------------
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NKRO is possible at least relatively new OS.
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Following OS supports both Extended and Bitmarp report.
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Windows7 64bit
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Windows2000 SP4
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Ubuntu 10.4(Linux 2.6)
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USB NKRO methods
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----------------
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1. Virtual keyboards
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Keyboard can increase its KRO by using virtual keyboards with Standard or Extended report.
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If the keyboard has 2 virtul keyboard with Standard report(6KRO), it gets 12KRO.
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Using this method means the keyboard is a composite device.
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2. Exteded report
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It needs large report size for this method to achive NKRO.
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If a keyboard has 101keys, it needs 103byte report. It seems to be inefficient.
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3. Bitmap report
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If the keyboard has less than 128keys, 16byte report will be enough for NKRO.
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The 16byte report seems to be reasonable cost to get NKRO.
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Report Format
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-------------
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Other report formats than followings are possible, though these format are typical one.
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1. Standard 8bytes
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modifiers(bitmap) 1byte
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reserved 1byte(not used)
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keys(array) 1byte*6
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Standard report can send 6keys plus 8modifiers simultaneously.
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Standard report is used by most keyboards in the marketplace.
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Standard report is identical to boot protocol report.
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Standard report is hard to suffer from compatibility problems.
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2. Extended standard 16,32,64bytes
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modifiers(bitmap) 1byte
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reserved 1byte(not used)
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keys(array) 1byte*(14,32,62)
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Extended report can send N-keys by using N+2bytes.
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Extended report is expected to be compatible with boot protocol.
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3. Bitmap 16,32,64bytes
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keys(bitmap) (16,32)bytes
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Bitmap report can send at most 128keys by 16bytes and 256keys by 32bytes.
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Bitmap report can achieve USB NKRO efficiently in terms of report size.
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Bitmap report needs a deliberation for boot protocol implementation.
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Compatibility Problem
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Some BIOS doesn't send SET_PROTCOL request, a keyboard can't switch to boot protocol mode.
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This may cuase a problem on a keyboard which uses other report than Standard.
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Windows Problem
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1. Windows accepts only 6keys in case of Standard report.
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It should be able to send 6keys plus 8modifiers.
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2. Windows accepts only 10keys in case of 16bytes Extended report.
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It should be able to send 14keys plus 8modifiers.
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3. Windows accepts only 18keys in case of 32bytes Extended report.
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It should be able to send 30keys plus 8modifiers.
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If keys are pressed in excess of the number, wrong keys are registered on Windows.
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This problem will be reportedly fixed soon.(2010/12/05)
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http://forums.anandtech.com/showpost.php?p=30873364&postcount=17
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EOF
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