[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

hal/src/main/native/sim/Alert.cpp

@@ -75,7 +75,7 @@ void HAL_SetAlertActive(HAL_AlertHandle alertHandle, HAL_Bool active,
       // Already active, do nothing (avoids cost of getting time)
       return;
     }
-    int64_t now = HAL_GetFPGATime(status);
+    int64_t now = HAL_GetMonotonicTime();
     int64_t expected = 0;
     // use compare-exchange to avoid potential race
     alert->activeStartTime.compare_exchange_strong(expected, now);

hal/src/main/native/sim/DriverStation.cpp

@@ -20,7 +20,7 @@
 #include "mockdata/DriverStationDataInternal.hpp"
 #include "wpi/hal/DriverStationTypes.h"
 #include "wpi/hal/Errors.h"
-#include "wpi/hal/cpp/fpga_clock.hpp"
+#include "wpi/hal/monotonic_clock.hpp"
 #include "wpi/hal/simulation/MockHooks.h"
 #include "wpi/util/EventVector.hpp"
 #include "wpi/util/mutex.hpp"
@@ -155,16 +155,16 @@ int32_t HAL_SendError(HAL_Bool isError, int32_t errorCode, HAL_Bool isLVCode,
   static constexpr int KEEP_MSGS = 5;
   std::scoped_lock lock(msgMutex);
   static std::string prevMsg[KEEP_MSGS];
-  static fpga_clock::time_point prevMsgTime[KEEP_MSGS];
+  static monotonic_clock::time_point prevMsgTime[KEEP_MSGS];
   static bool initialized = false;
   if (!initialized) {
     for (int i = 0; i < KEEP_MSGS; i++) {
-      prevMsgTime[i] = fpga_clock::now() - std::chrono::seconds(2);
+      prevMsgTime[i] = monotonic_clock::now() - std::chrono::seconds(2);
     }
     initialized = true;
   }
 
-  auto curTime = fpga_clock::now();
+  auto curTime = monotonic_clock::now();
   int i;
   for (i = 0; i < KEEP_MSGS; ++i) {
     if (prevMsg[i] == details) {

hal/src/main/native/sim/HAL.cpp

@@ -254,32 +254,8 @@ int32_t HAL_GetTeamNumber(void) {
   return HALSIM_GetRoboRioTeamNumber();
 }
 
-uint64_t HAL_GetFPGATime(int32_t* status) {
-  return wpi::hal::GetFPGATime();
-}
-
-uint64_t HAL_ExpandFPGATime(uint32_t unexpandedLower, int32_t* status) {
-  // Capture the current FPGA time.  This will give us the upper half of the
-  // clock.
-  uint64_t fpgaTime = HAL_GetFPGATime(status);
-  if (*status != 0) {
-    return 0;
-  }
-
-  // Now, we need to detect the case where the lower bits rolled over after we
-  // sampled.  In that case, the upper bits will be 1 bigger than they should
-  // be.
-
-  // Break it into lower and upper portions.
-  uint32_t lower = fpgaTime & 0xffffffffull;
-  uint64_t upper = (fpgaTime >> 32) & 0xffffffff;
-
-  // The time was sampled *before* the current time, so roll it back.
-  if (lower < unexpandedLower) {
-    --upper;
-  }
-
-  return (upper << 32) + static_cast<uint64_t>(unexpandedLower);
+uint64_t HAL_GetMonotonicTime(void) {
+  return wpi::hal::GetMonotonicTime();
 }
 
 HAL_Bool HAL_GetSystemActive(int32_t* status) {

hal/src/main/native/sim/MockHooks.cpp

@@ -25,7 +25,7 @@ static std::atomic<uint64_t> programStepTime{0};
 
 namespace wpi::hal::init {
 void InitializeMockHooks() {
-  wpi::util::SetNowImpl(GetFPGATime);
+  wpi::util::SetNowImpl(GetMonotonicTime);
 }
 }  // namespace wpi::hal::init
 
@@ -59,7 +59,7 @@ void StepTiming(uint64_t delta) {
   programStepTime += delta;
 }
 
-uint64_t GetFPGATime() {
+uint64_t GetMonotonicTime() {
   uint64_t curTime = programPauseTime;
   if (curTime == 0) {
     curTime = wpi::util::NowDefault();
@@ -67,10 +67,6 @@ uint64_t GetFPGATime() {
   return curTime + programStepTime - programStartTime;
 }
 
-double GetFPGATimestamp() {
-  return GetFPGATime() * 1.0e-6;
-}
-
 void SetProgramStarted(bool started) {
   programStarted = started;
 }
@@ -131,8 +127,7 @@ void HALSIM_StepTiming(uint64_t delta) {
   WaitNotifiers();
 
   while (delta > 0) {
-    int32_t status = 0;
-    uint64_t curTime = HAL_GetFPGATime(&status);
+    uint64_t curTime = HAL_GetMonotonicTime();
     uint64_t nextTimeout = HALSIM_GetNextNotifierTimeout();
     uint64_t step = (std::min)(delta, nextTimeout - curTime);
 

hal/src/main/native/sim/MockHooksInternal.hpp

@@ -17,9 +17,7 @@ bool IsTimingPaused();
 
 void StepTiming(uint64_t delta);
 
-uint64_t GetFPGATime();
-
-double GetFPGATimestamp();
+uint64_t GetMonotonicTime();
 
 void SetProgramStarted();
 }  // namespace wpi::hal

hal/src/main/native/sim/Notifier.cpp

@@ -93,8 +93,7 @@ void NotifierThread::Main() {
 
     // Wait until next alarm
     const Alarm& alarm = m_alarmQueue.top();
-    int32_t status = 0;
-    uint64_t curTime = HAL_GetFPGATime(&status);
+    uint64_t curTime = HAL_GetMonotonicTime();
     if (alarm.notifier->alarmTime > curTime) {
       m_cond.wait_for(
           lock, std::chrono::microseconds{alarm.notifier->alarmTime - curTime});
@@ -114,8 +113,7 @@ void NotifierThread::Main() {
 
 void NotifierThread::ProcessAlarms(
     wpi::util::SmallVectorImpl<HAL_NotifierHandle>* signaled) {
-  int32_t status = 0;
-  uint64_t curTime = HAL_GetFPGATime(&status);
+  uint64_t curTime = HAL_GetMonotonicTime();
 
   // Process alarms
   while (!m_alarmQueue.empty() &&
@@ -264,7 +262,7 @@ void HAL_SetNotifierAlarm(HAL_NotifierHandle notifierHandle, uint64_t alarmTime,
   }
 
   if (!absolute) {
-    alarmTime += HAL_GetFPGATime(status);
+    alarmTime += HAL_GetMonotonicTime();
   }
 
   uint64_t prevWakeup = UINT64_MAX;