USB_NKRO.txt

   1 USB NKRO MEMO
   2 =============
   3 2010/12/07
   4
   5
   6 References
   7 ----------
   8 USB - boot mode, NKRO, compatibility, etc...
   9     http://geekhack.org/showthread.php?t=13162
  10 NKey Rollover - Overview, Testing Methodology, and Results
  11     http://geekhack.org/showwiki.php?title=NKey+Rollover+-+Overview+Testing+Methodology+and+Results
  12
  13
  14 Terminogy
  15 ---------
  16 NKRO
  17 ghost
  18 matrix
  19 mechanical with diodes
  20 membrane
  21
  22
  23 OS Support Status
  24 -----------------
  25 NKRO is possible at least relatively new OS.
  26 Following OS supports both Extended and Bitmarp report.
  27     Windows7 64bit
  28     Windows2000 SP4
  29     Ubuntu 10.4(Linux 2.6)
  30
  31
  32 USB NKRO methods
  33 ----------------
  34 1. Virtual keyboards
  35     Keyboard can increase its KRO by using virtual keyboards with Standard or Extended report.
  36     If the keyboard has 2 virtul keyboard with Standard report(6KRO), it gets 12KRO.
  37     Using this method means the keyboard is a composite device.
  38
  39 2. Exteded report
  40     It needs large report size for this method to achive NKRO.
  41     If a keyboard has 101keys, it needs 103byte report. It seems to be inefficient.
  42
  43 3. Bitmap report
  44     If the keyboard has less than 128keys, 16byte report will be enough for NKRO.
  45     The 16byte report seems to be reasonable cost to get NKRO.
  46
  47
  48 Report Format
  49 -------------
  50 Other report formats than followings are possible, though these format are typical one.
  51
  52 1. Standard             8bytes
  53     modifiers(bitmap)       1byte
  54     reserved                1byte(not used)
  55     keys(array)             1byte*6
  56 Standard report can send 6keys plus 8modifiers simultaneously.
  57 Standard report is used by most keyboards in the marketplace.
  58 Standard report is identical to boot protocol report.
  59 Standard report is hard to suffer from compatibility problems.
  60
  61 2. Extended standard    16,32,64bytes
  62     modifiers(bitmap)       1byte
  63     reserved                1byte(not used)
  64     keys(array)             1byte*(14,32,62)
  65 Extended report can send N-keys by using N+2bytes.
  66 Extended report is expected to be compatible with boot protocol.
  67
  68 3. Bitmap               16,32,64bytes
  69     keys(bitmap)            (16,32)bytes
  70 Bitmap report can send at most 128keys by 16bytes and 256keys by 32bytes.
  71 Bitmap report can achieve USB NKRO efficiently in terms of report size.
  72 Bitmap report needs a deliberation for boot protocol implementation.
  73
  74
  75 Compatibility Problem
  76 ---------------------
  77 Some BIOS doesn't send SET_PROTCOL request, a keyboard can't switch to boot protocol mode.
  78 This may cuase a problem on a keyboard which uses other report than Standard.
  79
  80
  81 Windows Problem
  82 ---------------
  83 1. Windows accepts only 6keys  in case of Standard report.
  84         It should be able to send 6keys plus 8modifiers.
  85
  86 2. Windows accepts only 10keys in case of 16bytes Extended report.
  87         It should be able to send 14keys plus 8modifiers.
  88
  89 3. Windows accepts only 18keys in case of 32bytes Extended report.
  90         It should be able to send 30keys plus 8modifiers.
  91
  92 If keys are pressed in excess of the number, wrong keys are registered on Windows.
  93
  94
  95 This problem will be reportedly fixed soon.(2010/12/05)
  96     http://forums.anandtech.com/showpost.php?p=30873364&postcount=17
  97
  98
  99 EOF