[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

2 files changed, 3 insertions, 2 deletions

diff --git a/platforms/chibios/drivers/serial.c b/platforms/chibios/drivers/serial.c
index 3fae5cd3a4..0dd8e71ae8 100644
--- a/platforms/chibios/drivers/serial.c
+++ b/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
diff --git a/platforms/chibios/drivers/vendor/RP/RP2040/serial_vendor.c b/platforms/chibios/drivers/vendor/RP/RP2040/serial_vendor.c
index d933dc1f5d..338146dadd 100644
--- a/platforms/chibios/drivers/vendor/RP/RP2040/serial_vendor.c
+++ b/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);