Add DMA support to HAL and WPILibC (#2080)

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

@@ -222,6 +222,28 @@ int64_t HAL_GetFPGARevision(int32_t* status) {
 
 uint64_t HAL_GetFPGATime(int32_t* status) { return hal::GetFPGATime(); }
 
+uint64_t HAL_ExpandFPGATime(uint32_t unexpanded_lower, int32_t* status) {
+  // Capture the current FPGA time.  This will give us the upper half of the
+  // clock.
+  uint64_t fpga_time = 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 = fpga_time & 0xffffffffull;
+  uint64_t upper = (fpga_time >> 32) & 0xffffffff;
+
+  // The time was sampled *before* the current time, so roll it back.
+  if (lower < unexpanded_lower) {
+    --upper;
+  }
+
+  return (upper << 32) + static_cast<uint64_t>(unexpanded_lower);
+}
+
 HAL_Bool HAL_GetFPGAButton(int32_t* status) {
   return SimRoboRioData[0].fpgaButton;
 }