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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
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