add kinT kinesis keyboard controller (kint41 variant) (#13333)

fixes https://github.com/kinx-project/kint/issues/5

keyboards/kinesis/kint41/kint41.c

@@ -0,0 +1,52 @@
+/* Copyright 2020 QMK
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "kint41.h"
+
+void matrix_init_kb(void) {
+    matrix_init_user();
+
+// Turn on the Teensy 4.x Power LED:
+#define LED_POWER LINE_PIN13
+    setPinOutput(LED_POWER);
+    writePinHigh(LED_POWER);
+}
+
+// delay_inline sleeps for |cycles| (e.g. sleeping for F_CPU will sleep 1s).
+// delay_inline assumes the cycle counter has already been initialized and
+// should not be modified, i.e. it is safe to call during keyboard matrix scan.
+//
+// ChibiOS enables the cycle counter in chcore_v7m.c:
+// https://github.com/ChibiOS/ChibiOS/blob/b63023915c304092acb9f33bbab40f3ec07a7f0e/os/common/ports/ARMCMx/chcore_v7m.c#L263
+static void delay_inline(const uint32_t cycles) {
+  const uint32_t start = DWT->CYCCNT;
+  while ((DWT->CYCCNT - start) < cycles) {
+    // busy-loop until time has passed
+  }
+}
+
+void matrix_output_unselect_delay(void) {
+  // Use the cycle counter to do precise timing in microseconds. The ChibiOS
+  // thread sleep functions only allow sleep durations starting at 1 tick, which
+  // is 100μs in our configuration.
+
+  // Empirically: e.g. 5μs is not enough, will result in keys that don’t work
+  // and ghost key presses. 10μs seems to work well.
+
+  // 600 cycles at 0.6 cycles/ns == 1μs
+  const uint32_t cycles_per_us = 600;
+  delay_inline(10 * cycles_per_us);
+}