Support using a timer for wait_us() on ChibiOS-based boards (#12211)

* Support using a timer for wait_us() on ChibiOS-based boards (#12198)

There are spare GPT timers that can be used to get a more accurate
wait_ms() time. This is required for the matrix scan unselect delay (30µs)
to be shorter than the system tick rate of 100µs.

This is limited to the maximum GPT duration of 65535 so values above that
will automatically use the previous implementation based on the system
tick.

Using a specific timer means it can't be shared by another thread at the
same time so when wait_us() is called from anything other than the main
thread it will use the system tick implementation too.

* Update tmk_core/common/chibios/wait.c

* Update tmk_core/common/chibios/wait.c

Co-authored-by: Joel Challis <git@zvecr.com>

1 files changed, 89 insertions, 0 deletions

diff --git a/tmk_core/common/chibios/_wait.c b/tmk_core/common/chibios/_wait.c
new file mode 100644
index 0000000000..1fbea2dd5e
--- /dev/null
+++ b/tmk_core/common/chibios/_wait.c
@@ -0,0 +1,89 @@
+/* Copyright 2021 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 3 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/>.
+ */
+
+#ifndef __OPTIMIZE__
+#    pragma message "Compiler optimizations disabled; wait_cpuclock() won't work as designed"
+#endif
+
+#define CLOCK_DELAY_NOP8 "nop\n\t nop\n\t nop\n\t nop\n\t   nop\n\t nop\n\t nop\n\t nop\n\t"
+
+__attribute__((always_inline)) static inline void wait_cpuclock(unsigned int n) { /* n: 1..135 */
+    /* The argument n must be a constant expression.
+     * That way, compiler optimization will remove unnecessary code. */
+    if (n < 1) {
+        return;
+    }
+    if (n > 8) {
+        unsigned int n8 = n / 8;
+        n               = n - n8 * 8;
+        switch (n8) {
+            case 16:
+                asm volatile(CLOCK_DELAY_NOP8::: "memory");
+            case 15:
+                asm volatile(CLOCK_DELAY_NOP8::: "memory");
+            case 14:
+                asm volatile(CLOCK_DELAY_NOP8::: "memory");
+            case 13:
+                asm volatile(CLOCK_DELAY_NOP8::: "memory");
+            case 12:
+                asm volatile(CLOCK_DELAY_NOP8::: "memory");
+            case 11:
+                asm volatile(CLOCK_DELAY_NOP8::: "memory");
+            case 10:
+                asm volatile(CLOCK_DELAY_NOP8::: "memory");
+            case 9:
+                asm volatile(CLOCK_DELAY_NOP8::: "memory");
+            case 8:
+                asm volatile(CLOCK_DELAY_NOP8::: "memory");
+            case 7:
+                asm volatile(CLOCK_DELAY_NOP8::: "memory");
+            case 6:
+                asm volatile(CLOCK_DELAY_NOP8::: "memory");
+            case 5:
+                asm volatile(CLOCK_DELAY_NOP8::: "memory");
+            case 4:
+                asm volatile(CLOCK_DELAY_NOP8::: "memory");
+            case 3:
+                asm volatile(CLOCK_DELAY_NOP8::: "memory");
+            case 2:
+                asm volatile(CLOCK_DELAY_NOP8::: "memory");
+            case 1:
+                asm volatile(CLOCK_DELAY_NOP8::: "memory");
+            case 0:
+                break;
+        }
+    }
+    switch (n) {
+        case 8:
+            asm volatile("nop" ::: "memory");
+        case 7:
+            asm volatile("nop" ::: "memory");
+        case 6:
+            asm volatile("nop" ::: "memory");
+        case 5:
+            asm volatile("nop" ::: "memory");
+        case 4:
+            asm volatile("nop" ::: "memory");
+        case 3:
+            asm volatile("nop" ::: "memory");
+        case 2:
+            asm volatile("nop" ::: "memory");
+        case 1:
+            asm volatile("nop" ::: "memory");
+        case 0:
+            break;
+    }
+}