[hal,wpilib] Rename FPGA clock to monotonic clock (#8672)

- Remove status return from HAL level (clock getting should never fail)
- Remove 32-bit timestamp expand function
- Make monotonic_clock.hpp (formerly fpga_clock.hpp) header-only and
move to root hal include directory

wpilibc/src/main/native/include/wpi/framework/TimedRobot.hpp

@@ -64,9 +64,10 @@ class TimedRobot : public IterativeRobotBase {
 
   /**
    * Return the system clock time in microseconds for the start of the current
-   * periodic loop. This is in the same time base as Timer.GetFPGATimestamp(),
-   * but is stable through a loop. It is updated at the beginning of every
-   * periodic callback (including the normal periodic loop).
+   * periodic loop. This is in the same time base as
+   * Timer.GetMonotonicTimestamp(), but is stable through a loop. It is updated
+   * at the beginning of every periodic callback (including the normal periodic
+   * loop).
    *
    * @return Robot running time in microseconds, as of the start of the current
    * periodic function.
@@ -107,11 +108,11 @@ class TimedRobot : public IterativeRobotBase {
              std::chrono::microseconds period, std::chrono::microseconds offset)
         : func{std::move(func)},
           period{period},
-          expirationTime(
-              startTime + offset + period +
-              (std::chrono::microseconds{wpi::RobotController::GetFPGATime()} -
-               startTime) /
-                  period * period) {}
+          expirationTime(startTime + offset + period +
+                         (std::chrono::microseconds{
+                              wpi::RobotController::GetMonotonicTime()} -
+                          startTime) /
+                             period * period) {}
 
     bool operator>(const Callback& rhs) const {
       return expirationTime > rhs.expirationTime;

wpilibc/src/main/native/include/wpi/hardware/motor/MotorSafety.hpp

@@ -114,7 +114,7 @@ class MotorSafety {
   bool m_enabled = false;
 
   // The FPGA clock value when the motor has expired
-  wpi::units::second_t m_stopTime = Timer::GetFPGATimestamp();
+  wpi::units::second_t m_stopTime = Timer::GetMonotonicTimestamp();
 
   mutable wpi::util::mutex m_thisMutex;
 };

wpilibc/src/main/native/include/wpi/opmode/PeriodicOpMode.hpp

@@ -91,9 +91,10 @@ class PeriodicOpMode : public OpMode {
 
   /**
    * Return the system clock time in microseconds for the start of the current
-   * periodic loop. This is in the same time base as Timer.getFPGATimestamp(),
-   * but is stable through a loop. It is updated at the beginning of every
-   * periodic callback (including the normal periodic loop).
+   * periodic loop. This is in the same time base as
+   * Timer::GetMonotonicTimestamp(), but is stable through a loop. It is updated
+   * at the beginning of every periodic callback (including the normal periodic
+   * loop).
    *
    * @return Robot running time in microseconds, as of the start of the current
    * periodic function.

wpilibc/src/main/native/include/wpi/system/RobotController.hpp

@@ -60,22 +60,21 @@ class RobotController {
   static void SetTimeSource(std::function<uint64_t()> supplier);
 
   /**
-   * Read the microsecond timestamp. By default, the time is based on the FPGA
-   * hardware clock in microseconds since the FPGA started. However, the return
-   * value of this method may be modified to use any time base, including
-   * non-monotonic and non-continuous time bases.
+   * Read the microsecond timestamp. By default, the time is based on the
+   * monotonic clock. However, the return value of this method may be modified
+   * to use any time base, including non-monotonic and non-continuous time
+   * bases.
    *
    * @return The current time in microseconds.
    */
   static uint64_t GetTime();
 
   /**
-   * Read the microsecond-resolution timer on the FPGA.
+   * Read the microsecond-resolution monotonic timer.
    *
-   * @return The current time in microseconds according to the FPGA (since FPGA
-   *         reset).
+   * @return The current monotonic time in microseconds.
    */
-  static uint64_t GetFPGATime();
+  static uint64_t GetMonotonicTime();
 
   /**
    * Read the battery voltage.

wpilibc/src/main/native/include/wpi/system/Timer.hpp

@@ -25,7 +25,7 @@ void Wait(wpi::units::second_t seconds);
  * @return The time, just in case you want the robot to start autonomous at 8pm
  *         on Saturday.
  */
-wpi::units::second_t GetTime();
+wpi::units::second_t GetSystemTime();
 
 /**
  * A timer class.
@@ -119,24 +119,22 @@ class Timer {
   bool IsRunning() const;
 
   /**
-   * Return the clock time in seconds. By default, the time is based on the FPGA
-   * hardware clock in seconds since the FPGA started. However, the return value
-   * of this method may be modified to use any time base, including
-   * non-monotonic time bases.
+   * Return the clock time in seconds. By default, the time is the time returned
+   * by GetMonotonicTimestamp(). However, the return value of this method may be
+   * modified to use any time base, including non-monotonic time bases.
    *
    * @returns Robot running time in seconds.
    */
   static wpi::units::second_t GetTimestamp();
 
   /**
-   * Return the FPGA system clock time in seconds.
+   * Return the monotonic clock time in seconds.
    *
-   * Return the time from the FPGA hardware clock in seconds since the FPGA
-   * started. Rolls over after 71 minutes.
+   * Return the time from the monotonic clock in seconds.
    *
-   * @returns Robot running time in seconds.
+   * @returns Monotonic time in seconds.
    */
-  static wpi::units::second_t GetFPGATimestamp();
+  static wpi::units::second_t GetMonotonicTimestamp();
 
   /**
    * Return the approximate match time. The FMS does not send an official match

wpilibc/src/main/native/include/wpi/system/Tracer.hpp

@@ -7,7 +7,7 @@
 #include <chrono>
 #include <string_view>
 
-#include "wpi/hal/cpp/fpga_clock.hpp"
+#include "wpi/hal/monotonic_clock.hpp"
 #include "wpi/util/StringMap.hpp"
 
 namespace wpi::util {
@@ -65,9 +65,9 @@ class Tracer {
  private:
   static constexpr std::chrono::milliseconds kMinPrintPeriod{1000};
 
-  wpi::hal::fpga_clock::time_point m_startTime;
-  wpi::hal::fpga_clock::time_point m_lastEpochsPrintTime =
-      wpi::hal::fpga_clock::epoch();
+  wpi::hal::monotonic_clock::time_point m_startTime;
+  wpi::hal::monotonic_clock::time_point m_lastEpochsPrintTime =
+      wpi::hal::monotonic_clock::epoch();
 
   wpi::util::StringMap<std::chrono::nanoseconds> m_epochs;
 };