USB NKRO MEMO
=============
-2010/12/07
+2010/12/09
References
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
Terminogy
OS Support Status
-----------------
-NKRO is possible at least relatively new OS.
-Following OS supports both Extended and Bitmarp report.
+USB NKRO is possible *without* a custom driver.
+At least following OSes supports.
Windows7 64bit
+ WindowsXP
Windows2000 SP4
- Ubuntu 10.4(Linux 2.6)
+ Ubuntu10.4(Linux 2.6)
+ MacOSX(To be tested)
+
+
+Custom Driver for USB NKRO
+--------------------------
+NOT NEEDED
+at least when using fllowing 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 virtul keyboard with Standard report(6KRO), it gets 12KRO.
+ 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. Exteded report
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.
-
-
-Compatibility Problem
----------------------
-Some BIOS doesn't send SET_PROTCOL request, a keyboard can't switch to boot protocol mode.
-This may cuase a problem on a keyboard which uses other report than Standard.
+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_PROTCOL request, a keyboard can't switch to boot protocol mode.
+ This may cuase 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
projects / tmk_firmware.git / blobdiff