implemented algorithm to prevent ghost-keys

firmware/main.c

@@ -289,6 +289,7 @@ static void hardwareInit(void) {
 /* ------------------------------------------------------------------------- */
 
 static uint8_t reportBuffer[8]; ///< buffer for HID reports
+static uint8_t oldReportBuffer[8]; ///< buffer for the last sent HID report
 static uint8_t idleRate;        ///< in 4ms units
 static uint8_t protocolVer = 1; ///< 0 = boot protocol, 1 = report protocol
 uint8_t expectReport = 0;       ///< flag to indicate if we expect an USB-report
@@ -428,6 +429,7 @@ void usbSendReport(uint8_t mode, uint8_t key) {
 /* ------------------------------------------------------------------------- */
 
 uint8_t curmatrix[16];  ///< contains current state of the keyboard
+uint8_t ghostmatrix[16]; ///< contains pressed keys that belong to a ghost-key situation
 
 /**
  * The keymatrix-array contains positions of keys in the matrix. Here you can
@@ -493,7 +495,7 @@ typedef struct {
 /**
  * Convert an ASCII-character to the corresponding key-code and modifier-code
  * combination.
- * \parm character ASCII-character to convert
+ * \param character ASCII-character to convert
  * \return structure containing the combination
  */
 Key charToKey(char character) {
@@ -670,6 +672,31 @@ void printMatrix(void) {
     sendString("---");
 }
 
+/**
+ * Checks if more than one bit in data is set.
+ * \param data value to check
+ * \return true if more than one bit is set
+ */
+uint8_t bitcount2(uint16_t data) {
+    data &= (data - 1);
+    return data != 0;
+}
+
+/**
+ * check if reportBuffer contains the key
+ * \param buffer buffer to check
+ * \param key key to search
+ * \return 1 if buffer contains key, 0 otherwise
+ */
+uint8_t bufferContains(uint8_t* buffer, uint8_t key) {
+    for (uint8_t i = 2; i < sizeof(buffer); i++) {
+        if (buffer[i] == key) {
+            return 1;
+        }
+    }
+    return 0;
+}
+
 /**
  * Scan and debounce keypresses. This is the main worker function for normal
  * keyboard operation, the code contains lot of comments. Basically, it first
@@ -679,7 +706,8 @@ void printMatrix(void) {
  * so we can be pretty sure that the keys are in a certain state (as in: not
  * bouncing). Then, the codes for keys and modifiers are searched from the two
  * arrays, the USB-message to send the state is prepared. The return value of
- * this function indicates if the message has to be sent.
+ *~ this function indicates if the message has to be sent.
+
  * \return flag to indicate whether something has changed
  */
 uint8_t scankeys(void) {
@@ -703,6 +731,14 @@ uint8_t scankeys(void) {
         }
         _delay_us(30);
         uint8_t data = ~PINCOLUMNS;
+        // check if we have to prevent ghost-keys
+        uint16_t rows= (PINROWS1 << 8) | PINROWS2;
+        if (bitcount2(~rows) && bitcount2(data)) {
+            // ghost-key situation detected
+            ghostmatrix[row] = data;
+        } else {
+            ghostmatrix[row] = 0x00;
+        }
         if (data != curmatrix[row]) {
             // if a change was detected
             debounce = 10; // activate debounce counter
@@ -721,13 +757,15 @@ uint8_t scankeys(void) {
             uint8_t data = curmatrix[row]; // restore buffer
             if (data != 0xff) { // anything on this row? - optimization
                 for (uint8_t col = 0; col <= 7; col++) { // check every bit on this row
-                    uint8_t key, modifier;
+                    uint8_t key, modifier, isghostkey;
                     if (data & (1 << col)) {
                         key = pgm_read_byte(&keymatrix[row][col]);
                         modifier = pgm_read_byte(&modmatrix[row][col]);
+                        isghostkey = ghostmatrix[row] & (1 << col);
                     } else {
                         key = KEY_Reserved;
                         modifier = MOD_NONE;
+                        isghostkey = 0x00;
                     }
                     if (key != KEY_Reserved) { // keycode should be added to report
                         if (reportIndex >= sizeof(reportBuffer)) { // too many keycodes
@@ -736,9 +774,18 @@ uint8_t scankeys(void) {
                                 retval |= 0x02; // continue decoding to get modifiers
                             }
                         } else {
+                            if (isghostkey) {
+                                // we're in a ghost-key situation
+                                if (bufferContains(oldReportBuffer, key)) {
+                                    // this key has been pressed before, so we still send it
                                     reportBuffer[reportIndex] = key; // set next available entry
                                     reportIndex++;
                                 }
+                            } else {
+                                reportBuffer[reportIndex] = key; // set next available entry
+                                reportIndex++;
+                            }
+                        }
                     }
                     if (modifier != MOD_NONE) { // modifier should be added to report
                         reportBuffer[0] |= modifier;
@@ -766,6 +813,8 @@ int main(void) {
     usbInit();
     sei();
 
+    memset(oldReportBuffer, 0, sizeof(oldReportBuffer)); // clear old report buffer
+
     scankeys();
     while (1) {
         // main event loop
@@ -790,6 +839,7 @@ int main(void) {
         if (updateNeeded && usbInterruptIsReady()) {
             updateNeeded = 0;
             usbSetInterrupt(reportBuffer, sizeof(reportBuffer));
+            memcpy(oldReportBuffer, reportBuffer, sizeof(oldReportBuffer));
         }
     }
     return 0;