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