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diff --git a/docs/usb_nkro.txt b/docs/usb_nkro.txt new file mode 100644 index 0000000000..d9f1d12292 --- /dev/null +++ b/docs/usb_nkro.txt @@ -0,0 +1,160 @@ +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 |