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sim: More rigorous clocking comments

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The language describing the clockEdge and nextCycle functions were ambiguous,
and so were prone to misinterpretation/misuse. Clear up the comments to more
rigorously describe their functionality.
This commit is contained in:
Joel Hestness 2014-06-09 22:01:16 -05:00
parent fbe3688de3
commit 4f8ac94549
1 changed files with 21 additions and 10 deletions
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31
src/sim/clocked_object.hh
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@ -79,7 +79,8 @@ class ClockedObject : public SimObject
ClockedObject& operator=(ClockedObject&);
/**
* Align cycle and tick to the next clock edge if not already done.
* Align cycle and tick to the next clock edge if not already done. When
* complete, tick must be at least curTick().
*/
void update() const
{
@ -154,13 +155,18 @@ class ClockedObject : public SimObject
}
/**
* Determine the tick when a cycle begins, by default the current
* one, but the argument also enables the caller to determine a
* future cycle.
* Determine the tick when a cycle begins, by default the current one, but
* the argument also enables the caller to determine a future cycle. When
* curTick() is on a clock edge, the number of cycles in the parameter is
* added to curTick() to be returned. When curTick() is not aligned to a
* clock edge, the number of cycles in the parameter is added to the next
* clock edge.
*
* @param cycles The number of cycles into the future
*
* @return The tick when the clock edge occurs
* @return The start tick when the requested clock edge occurs. Precisely,
* this tick can be
* curTick() + [0, clockPeriod()) + clockPeriod() * cycles
*/
inline Tick clockEdge(Cycles cycles = Cycles(0)) const
{
@ -175,7 +181,9 @@ class ClockedObject : public SimObject
* Determine the current cycle, corresponding to a tick aligned to
* a clock edge.
*
* @return The current cycle count
* @return When curTick() is on a clock edge, return the Cycle corresponding
* to that clock edge. When curTick() is not on a clock edge, return the
* Cycle corresponding to the next clock edge.
*/
inline Cycles curCycle() const
{
@ -186,11 +194,14 @@ class ClockedObject : public SimObject
}
/**
* Based on the clock of the object, determine the tick when the next
* cycle begins, in other words, return the next clock edge.
* (This can never be the current tick.)
* Based on the clock of the object, determine the start tick of the first
* cycle that is at least one cycle in the future. When curTick() is at the
* current cycle edge, this returns the next clock edge. When calling this
* during the middle of a cycle, this returns 2 clock edges in the future.
*
* @return The tick when the next cycle starts
* @return The start tick of the first cycle that is at least one cycle in
* the future. Precisely, the returned tick can be in the range
* curTick() + [clockPeriod(), 2 * clockPeriod())
*/
Tick nextCycle() const
{ return clockEdge(Cycles(1)); }