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diff --git a/USB_NKRO.txt b/USB_NKRO.txt new file mode 100644 index 0000000000..9bd8f704c3 --- /dev/null +++ b/USB_NKRO.txt @@ -0,0 +1,99 @@ +USB NKRO MEMO +============= +2010/12/07 + + +References +---------- +USB - boot mode, NKRO, compatibility, etc... + http://geekhack.org/showthread.php?t=13162 +NKey Rollover - Overview, Testing Methodology, and Results + http://geekhack.org/showwiki.php?title=NKey+Rollover+-+Overview+Testing+Methodology+and+Results + + +Terminogy +--------- +NKRO +ghost +matrix +mechanical with diodes +membrane + + +OS Support Status +----------------- +NKRO is possible at least relatively new OS. +Following OS supports both Extended and Bitmarp report. + Windows7 64bit + Windows2000 SP4 + Ubuntu 10.4(Linux 2.6) + + +USB NKRO methods +---------------- +1. Virtual keyboards + Keyboard can increase its KRO by using virtual keyboards with Standard or Extended report. + If the keyboard has 2 virtul keyboard with Standard report(6KRO), it gets 12KRO. + Using this method means the keyboard is a composite device. + +2. Exteded report + It needs large report size for this method to achive NKRO. + If a keyboard has 101keys, it needs 103byte report. It seems to be inefficient. + +3. Bitmap report + If the keyboard has less than 128keys, 16byte report will be enough for NKRO. + The 16byte report seems to be reasonable cost to get NKRO. + + +Report Format +------------- +Other report formats than followings are possible, though these format are typical one. + +1. Standard 8bytes + modifiers(bitmap) 1byte + reserved 1byte(not used) + keys(array) 1byte*6 +Standard report can send 6keys plus 8modifiers simultaneously. +Standard report is used by most keyboards in the marketplace. +Standard report is identical to boot protocol report. +Standard report is hard to suffer from compatibility problems. + +2. Extended standard 16,32,64bytes + modifiers(bitmap) 1byte + reserved 1byte(not used) + keys(array) 1byte*(14,32,62) +Extended report can send N-keys by using N+2bytes. +Extended report is expected to be compatible with boot protocol. + +3. Bitmap 16,32,64bytes + keys(bitmap) (16,32)bytes +Bitmap report can send at most 128keys by 16bytes and 256keys by 32bytes. +Bitmap report can achieve USB NKRO efficiently in terms of report size. +Bitmap report needs a deliberation for boot protocol implementation. + + +Compatibility Problem +--------------------- +Some BIOS doesn't send SET_PROTCOL request, a keyboard can't switch to boot protocol mode. +This may cuase a problem on a keyboard which uses other report than Standard. + + +Windows Problem +--------------- +1. Windows accepts only 6keys in case of Standard report. + It should be able to send 6keys plus 8modifiers. + +2. Windows accepts only 10keys in case of 16bytes Extended report. + It should be able to send 14keys plus 8modifiers. + +3. Windows accepts only 18keys in case of 32bytes Extended report. + It should be able to send 30keys plus 8modifiers. + +If keys are pressed in excess of the number, wrong keys are registered on Windows. + + +This problem will be reportedly fixed soon.(2010/12/05) + http://forums.anandtech.com/showpost.php?p=30873364&postcount=17 + + +EOF |