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>

4 files changed, 127 insertions, 79 deletions

diff --git a/tmk_core/chibios.mk b/tmk_core/chibios.mk
index 7962516a0..18839710b 100644
--- a/tmk_core/chibios.mk
+++ b/tmk_core/chibios.mk
@@ -211,7 +211,8 @@ CHIBISRC = $(STARTUPSRC) \
        $(BOARDSRC) \
        $(STREAMSSRC) \
        $(CHIBIOS)/os/various/syscalls.c \
-       $(PLATFORM_COMMON_DIR)/syscall-fallbacks.c
+       $(PLATFORM_COMMON_DIR)/syscall-fallbacks.c \
+       $(PLATFORM_COMMON_DIR)/wait.c
 
 # Ensure the ASM files are not subjected to LTO -- it'll strip out interrupt handlers otherwise.
 QUANTUM_LIB_SRC += $(STARTUPASM) $(PORTASM) $(OSALASM) $(PLATFORMASM)
diff --git a/tmk_core/common/chibios/_wait.c b/tmk_core/common/chibios/_wait.c
new file mode 100644
index 000000000..1fbea2dd5
--- /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;
+    }
+}
diff --git a/tmk_core/common/chibios/_wait.h b/tmk_core/common/chibios/_wait.h
index 5bface53e..4a5172536 100644
--- a/tmk_core/common/chibios/_wait.h
+++ b/tmk_core/common/chibios/_wait.h
@@ -16,6 +16,7 @@
 #pragma once
 
 #include <ch.h>
+#include <hal.h>
 
 /* chThdSleepX of zero maps to infinite - so we map to a tiny delay to still yield */
 #define wait_ms(ms)                     \
@@ -26,14 +27,19 @@
             chThdSleepMicroseconds(1);  \
         }                               \
     } while (0)
-#define wait_us(us)                     \
-    do {                                \
-        if (us != 0) {                  \
-            chThdSleepMicroseconds(us); \
-        } else {                        \
-            chThdSleepMicroseconds(1);  \
-        }                               \
-    } while (0)
+
+#ifdef WAIT_US_TIMER
+void wait_us(uint16_t duration);
+#else
+#    define wait_us(us)                     \
+        do {                                \
+            if (us != 0) {                  \
+                chThdSleepMicroseconds(us); \
+            } else {                        \
+                chThdSleepMicroseconds(1);  \
+            }                               \
+        } while (0)
+#endif
 
 /* For GPIOs on ARM-based MCUs, the input pins are sampled by the clock of the bus
  * to which the GPIO is connected.
@@ -46,7 +52,7 @@
  * (A fairly large value of 0.25 microseconds is set.)
  */
 
-#include "wait.c"
+#include "_wait.c"
 
 #ifndef GPIO_INPUT_PIN_DELAY
 #    define GPIO_INPUT_PIN_DELAY (STM32_SYSCLK / 1000000L / 4)
diff --git a/tmk_core/common/chibios/wait.c b/tmk_core/common/chibios/wait.c
index c6270fd95..56fd6ffce 100644
--- a/tmk_core/common/chibios/wait.c
+++ b/tmk_core/common/chibios/wait.c
@@ -14,76 +14,28 @@
  * 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
+#include <ch.h>
+#include <hal.h>
 
-#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"
+#include "_wait.h"
 
-__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;
-        }
+#ifdef WAIT_US_TIMER
+void wait_us(uint16_t duration) {
+    static const GPTConfig gpt_cfg = {1000000, NULL, 0, 0}; /* 1MHz timer, no callback */
+
+    if (duration == 0) {
+        duration = 1;
     }
-    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;
+
+    /*
+     * Only use this timer on the main thread;
+     * other threads need to use their own timer.
+     */
+    if (chThdGetSelfX() == &ch.mainthread && duration < (1ULL << (sizeof(gptcnt_t) * 8))) {
+        gptStart(&WAIT_US_TIMER, &gpt_cfg);
+        gptPolledDelay(&WAIT_US_TIMER, duration);
+    } else {
+        chThdSleepMicroseconds(duration);
     }
-}
\ No newline at end of file
+}
+#endif