[Core] Use polled waiting on ChibiOS platforms that support it (#17607)

* Use polled waiting on platforms that support it

Due to context switching overhead waiting a very short amount of time on
a sleeping thread is often not accurate and in fact not usable for timing
critical usage i.e. in a driver. Thus we use polled waiting for ranges
in the us range on platforms that support it instead. The fallback is
the thread sleeping mechanism.

This includes:

* ARM platforms with CYCCNT register (ARMv7, ARMv8) this is
  incremented at CPU clock frequency
* GD32VF103 RISC-V port with CSR_MCYCLE register this is incremented at
  CPU clock frequency
* RP2040 ARMv6 port which uses the integrated timer peripheral which is
  incremented with a fixed 1MHz frequency

* Use wait_us() instead of chSysPolledDelayX

...as it is powered by busy waiting now.

* Add chibios waiting methods test bench

platforms/chibios/_wait.h

@@ -30,6 +30,11 @@
 
 #ifdef WAIT_US_TIMER
 void wait_us(uint16_t duration);
+#elif PORT_SUPPORTS_RT == TRUE
+#    define wait_us(us)                                            \
+        do {                                                       \
+            chSysPolledDelayX(US2RTC(REALTIME_COUNTER_CLOCK, us)); \
+        } while (0)
 #else
 #    define wait_us(us)                     \
         do {                                \

platforms/chibios/bootloaders/rp2040.c

@@ -43,9 +43,8 @@ void __late_init(void) {
     if (magic_location != magic_token) {
         magic_location = magic_token;
         // ChibiOS is not initialized at this point, so sleeping is only
-        // possible via busy waiting. The internal timer peripheral is running
-        // at this point with a precision of 1us.
-        chSysPolledDelayX(MS2RTC(1 * MHZ, RP2040_BOOTLOADER_DOUBLE_TAP_RESET_TIMEOUT));
+        // possible via busy waiting.
+        wait_us(RP2040_BOOTLOADER_DOUBLE_TAP_RESET_TIMEOUT * 1000U);
         magic_location = 0;
         return;
     }

platforms/chibios/chibios_config.h

@@ -21,6 +21,9 @@
 
 #if defined(MCU_RP)
 #    define CPU_CLOCK RP_CORE_CLK
+// ChibiOS uses the RP2040 timer peripheral as its real time counter, this timer
+// is monotonic and running at 1MHz.
+#    define REALTIME_COUNTER_CLOCK 1000000
 
 #    define USE_GPIOV1
 #    define PAL_OUTPUT_TYPE_OPENDRAIN _Static_assert(0, "RP2040 has no Open Drain GPIO configuration, setting this is not possible");
@@ -102,6 +105,11 @@
 #    endif
 #endif
 
+#if defined(MCU_MIMXRT1062)
+#    include "clock_config.h"
+#    define CPU_CLOCK BOARD_BOOTCLOCKRUN_CORE_CLOCK
+#endif
+
 #if defined(HT32)
 #    define CPU_CLOCK HT32_CK_SYS_FREQUENCY
 #    define PAL_MODE_ALTERNATE PAL_HT32_MODE_AF
@@ -109,3 +117,7 @@
 #    define PAL_OUTPUT_TYPE_PUSHPULL PAL_HT32_MODE_DIR
 #    define PAL_OUTPUT_SPEED_HIGHEST 0
 #endif
+
+#if !defined(REALTIME_COUNTER_CLOCK)
+#    define REALTIME_COUNTER_CLOCK CPU_CLOCK
+#endif

platforms/chibios/drivers/serial.c

@@ -20,7 +20,8 @@
 #    error "chSysPolledDelayX method not supported on this platform"
 #else
 #    undef wait_us
-#    define wait_us(x) chSysPolledDelayX(US2RTC(CPU_CLOCK, x))
+// Force usage of polled waiting - in case WAIT_US_TIMER is activated
+#    define wait_us(us) chSysPolledDelayX(US2RTC(REALTIME_COUNTER_CLOCK, us))
 #endif
 
 #ifndef SELECT_SOFT_SERIAL_SPEED

platforms/chibios/drivers/vendor/RP/RP2040/serial_vendor.c

@@ -152,7 +152,7 @@ static inline void enter_rx_state(void) {
     }
     // Wait for ~11 bits, 1 start bit + 8 data bits + 1 stop bit + 1 bit
     // headroom.
-    chSysPolledDelayX(US2RTC(1 * MHZ, (1000000U * 11 / SERIAL_USART_SPEED)));
+    wait_us(1000000U * 11U / SERIAL_USART_SPEED);
     // Disable tx state machine to not interfere with our tx pin manipulation
     pio_sm_set_enabled(pio, tx_state_machine, false);
     gpio_set_drive_strength(SERIAL_USART_TX_PIN, GPIO_DRIVE_STRENGTH_2MA);