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-USB NKRO MEMO
-=============
-2010/12/09
-
-
-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
-dfj's NKRO(2010/06)
- http://geekhack.org/showpost.php?p=191195&postcount=251
- http://geekhack.org/showthread.php?p=204389#post204389
-
-
-Terminology
----------
-NKRO
-ghost
-matrix
-mechanical with diodes
-membrane
-
-
-OS Support Status
------------------
-USB NKRO is possible *without* a custom driver.
-At least following OS's supports.
- Windows7 64bit
- WindowsXP
- Windows2000 SP4
- Ubuntu10.4(Linux 2.6)
- MacOSX(To be tested)
-
-
-Custom Driver for USB NKRO
---------------------------
-NOT NEEDED
-at least when using following report formats on Windows, Linux or MacOSX.
-
-
-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 virtual keyboard with Standard report(6KRO), it gets 12KRO.
- Using this method means the keyboard is a composite device.
-
-2. Extended report
- It needs large report size for this method to achieve 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.
-Bitmap report descriptor sample:
- 0x05, 0x01, // Usage Page (Generic Desktop),
- 0x09, 0x06, // Usage (Keyboard),
- 0xA1, 0x01, // Collection (Application),
- // bitmap of modifiers
- 0x75, 0x01, // Report Size (1),
- 0x95, 0x08, // Report Count (8),
- 0x05, 0x07, // Usage Page (Key Codes),
- 0x19, 0xE0, // Usage Minimum (224),
- 0x29, 0xE7, // Usage Maximum (231),
- 0x15, 0x00, // Logical Minimum (0),
- 0x25, 0x01, // Logical Maximum (1),
- 0x81, 0x02, // Input (Data, Variable, Absolute), ;Modifier byte
- // LED output report
- 0x95, 0x05, // Report Count (5),
- 0x75, 0x01, // Report Size (1),
- 0x05, 0x08, // Usage Page (LEDs),
- 0x19, 0x01, // Usage Minimum (1),
- 0x29, 0x05, // Usage Maximum (5),
- 0x91, 0x02, // Output (Data, Variable, Absolute),
- 0x95, 0x01, // Report Count (1),
- 0x75, 0x03, // Report Size (3),
- 0x91, 0x03, // Output (Constant),
- // bitmap of keys
- 0x95, (REPORT_BYTES-1)*8, // Report Count (),
- 0x75, 0x01, // Report Size (1),
- 0x15, 0x00, // Logical Minimum (0),
- 0x25, 0x01, // Logical Maximum(1),
- 0x05, 0x07, // Usage Page (Key Codes),
- 0x19, 0x00, // Usage Minimum (0),
- 0x29, (REPORT_BYTES-1)*8-1, // Usage Maximum (),
- 0x81, 0x02, // Input (Data, Variable, Absolute),
- 0xc0 // End Collection
-where REPORT_BYTES is a report size in bytes.
-
-
-Considerations
---------------
-Compatibility
- boot protocol
- minor/old system
- Some BIOS doesn't send SET_PROTOCOL request, a keyboard can't switch to boot protocol mode.
- This may cause a problem on a keyboard which uses other report than Standard.
-Reactivity
- USB polling time
- OS/Driver processing time
-
-
-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
-
-
-Tools for testing NKRO
-----------------------
-Browser App:
-http://www.microsoft.com/appliedsciences/content/projects/KeyboardGhostingDemo.aspx
-http://random.xem.us/rollover.html
-
-Windows:
-AquaKeyTest.exe http://geekhack.org/showthread.php?t=6643
-
-Linux:
-xkeycaps
-xev
-showkeys
-
-EOF