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ArmPlatformPkg/SP804TimerLib: Fix delay functions to be reentrant 

In the previous implementation, if the MicroSecondDelay or NanoSecondDelay
were called while a delay function was already running, the timer HW controller
was reinitialized with the new settings and it was discarding the settings
of the first called delay function.



git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@12163 6f19259b-4bc3-4df7-8a09-765794883524
This commit is contained in:
oliviermartin 2011-08-18 10:14:33 +00:00
parent 9e4a626c06
commit 2dde40b1ff
1 changed files with 92 additions and 29 deletions
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121
ArmPlatformPkg/Library/SP804TimerLib/SP804TimerLib.c
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@ -1,6 +1,7 @@
/** @file
Copyright (c) 2008 - 2010, Apple Inc. All rights reserved.<BR>
Copyright (c) 2011, ARM Limited. All rights reserved.
This program and the accompanying materials
are licensed and made available under the terms and conditions of the BSD License
@ -36,13 +37,10 @@ TimerConstructor (
if (MmioRead32(SP804_TIMER_METRONOME_BASE + SP804_TIMER_CONTROL_REG) & SP804_TIMER_CTRL_ENABLE) {
return RETURN_SUCCESS;
} else {
// Configure the Metronome Timer for one shot operation, 32 bits, no prescaler, and interrupt disabled
MmioOr32 (SP804_TIMER_METRONOME_BASE + SP804_TIMER_CONTROL_REG, SP804_TIMER_CTRL_ONESHOT | SP804_TIMER_CTRL_32BIT | SP804_PRESCALE_DIV_1);
// Configure the Metronome Timer for free running operation, 32 bits, no prescaler, and interrupt disabled
MmioWrite32 (SP804_TIMER_METRONOME_BASE + SP804_TIMER_CONTROL_REG, SP804_TIMER_CTRL_32BIT | SP804_PRESCALE_DIV_1);
// Preload the timer count register
MmioWrite32 (SP804_TIMER_METRONOME_BASE + SP804_TIMER_LOAD_REG, 1);
// Enable the timer
// Start the Metronome Timer ticking
MmioOr32 (SP804_TIMER_METRONOME_BASE + SP804_TIMER_CONTROL_REG, SP804_TIMER_CTRL_ENABLE);
}
@ -51,7 +49,7 @@ TimerConstructor (
return RETURN_SUCCESS;
} else {
// Configure the Performance timer for free running operation, 32 bits, no prescaler, interrupt disabled
MmioOr32 (SP804_TIMER_PERFORMANCE_BASE + SP804_TIMER_CONTROL_REG, SP804_TIMER_CTRL_32BIT | SP804_PRESCALE_DIV_1);
MmioWrite32 (SP804_TIMER_PERFORMANCE_BASE + SP804_TIMER_CONTROL_REG, SP804_TIMER_CTRL_32BIT | SP804_PRESCALE_DIV_1);
// Start the Performance Timer ticking
MmioOr32 (SP804_TIMER_PERFORMANCE_BASE + SP804_TIMER_CONTROL_REG, SP804_TIMER_CTRL_ENABLE);
@ -64,6 +62,26 @@ TimerConstructor (
Stalls the CPU for at least the given number of microseconds.
Stalls the CPU for the number of microseconds specified by MicroSeconds.
The hardware timer is 32 bits.
The maximum possible delay is (0xFFFFFFFF / TimerFrequencyMHz), i.e. ([32bits] / FreqInMHz)
For example:
+----------------+------------+----------+----------+
| TimerFrequency | MaxDelay | MaxDelay | MaxDelay |
| (MHz) | (us) | (s) | (min) |
+----------------+------------+----------+----------+
| 1 | 0xFFFFFFFF | 4294 | 71.5 |
| 5 | 0x33333333 | 859 | 14.3 |
| 10 | 0x19999999 | 429 | 7.2 |
| 50 | 0x051EB851 | 86 | 1.4 |
+----------------+------------+----------+----------+
If it becomes necessary to support higher delays, then consider using the
real time clock.
During this delay, the cpu is not yielded to any other process, with one exception:
events that are triggered off a timer and which execute at a higher TPL than
this function. These events may call MicroSecondDelay (or NanoSecondDelay) to
fulfil their own needs.
Therefore, this function must be re-entrant, as it may be interrupted and re-started.
@param MicroSeconds The minimum number of microseconds to delay.
@ -76,16 +94,68 @@ MicroSecondDelay (
IN UINTN MicroSeconds
)
{
UINTN Index;
UINT64 DelayTicks64; // Convert from microseconds to timer ticks, more bits to detect over-range conditions.
UINTN DelayTicks; // Convert from microseconds to timer ticks, native size for general calculations.
UINTN StartTicks; // Timer value snapshot at the start of the delay
UINTN TargetTicks; // Timer value to signal the end of the delay
UINTN CurrentTicks; // Current value of the 64-bit timer value at any given moment
// Reload the counter for each 1Mhz to avoid an overflow in the load value
for (Index = 0; Index < (UINTN)PcdGet32(PcdSP804TimerFrequencyInMHz); Index++) {
// load the timer count register
MmioWrite32 (SP804_TIMER_METRONOME_BASE + SP804_TIMER_LOAD_REG, MicroSeconds);
// If we snapshot the timer at the start of the delay function then we minimise unaccounted overheads.
StartTicks = MmioRead32 (SP804_TIMER_METRONOME_BASE + SP804_TIMER_CURRENT_REG);
while (MmioRead32 (SP804_TIMER_METRONOME_BASE + SP804_TIMER_CURRENT_REG) > 0) {
;
}
// We are operating at the limit of 32bits. For the range checking work in 64 bits to avoid overflows.
DelayTicks64 = MultU64x32((UINT64)MicroSeconds, PcdGet32(PcdSP804TimerFrequencyInMHz));
// We are limited to 32 bits.
// If the specified delay is exactly equal to the max range of the timer,
// then the start will be equal to the stop plus one timer overflow (wrap-around).
// To avoid having to check for that, reduce the maximum acceptable range by 1 tick,
// i.e. reject delays equal or greater than the max range of the timer.
if (DelayTicks64 >= (UINT64)SP804_MAX_TICKS) {
DEBUG((EFI_D_ERROR,"MicroSecondDelay: ERROR: MicroSeconds=%d exceed SP804 count range. Max MicroSeconds=%d\n",
MicroSeconds,
((UINTN)SP804_MAX_TICKS/PcdGet32(PcdSP804TimerFrequencyInMHz))));
}
ASSERT(DelayTicks64 < (UINT64)SP804_MAX_TICKS);
// From now on do calculations only in native bit size.
DelayTicks = (UINTN)DelayTicks64;
// Calculate the target value of the timer.
//Note: SP804 timer is counting down
if (StartTicks >= DelayTicks) {
// In this case we do not expect a wrap-around of the timer to occur.
// CurrentTicks must be less than StartTicks and higher than TargetTicks.
// If this is not the case, then the delay has been reached and may even have been exceeded if this
// function was suspended by a higher priority interrupt.
TargetTicks = StartTicks - DelayTicks;
do {
CurrentTicks = MmioRead32 (SP804_TIMER_METRONOME_BASE + SP804_TIMER_CURRENT_REG);
} while ((CurrentTicks > TargetTicks) && (CurrentTicks <= StartTicks));
} else {
// In this case TargetTicks is larger than StartTicks.
// This means we expect a wrap-around of the timer to occur and we must wait for it.
// Before the wrap-around, CurrentTicks must be less than StartTicks and less than TargetTicks.
// After the wrap-around, CurrentTicks must be larger than StartTicks and larger than TargetTicks.
// If this is not the case, then the delay has been reached and may even have been exceeded if this
// function was suspended by a higher priority interrupt.
// The order of operations is essential to avoid arithmetic overflow problems
TargetTicks = ((UINTN)SP804_MAX_TICKS - DelayTicks) + StartTicks;
// First wait for the wrap-around to occur
do {
CurrentTicks = MmioRead32 (SP804_TIMER_METRONOME_BASE + SP804_TIMER_CURRENT_REG);
} while (CurrentTicks <= StartTicks);
// Then wait for the target
do {
CurrentTicks = MmioRead32 (SP804_TIMER_METRONOME_BASE + SP804_TIMER_CURRENT_REG);
} while (CurrentTicks > TargetTicks);
}
return MicroSeconds;
@ -96,6 +166,9 @@ MicroSecondDelay (
Stalls the CPU for the number of nanoseconds specified by NanoSeconds.
When the timer frequency is 1MHz, each tick corresponds to 1 microsecond.
Therefore, the nanosecond delay will be rounded up to the nearest 1 microsecond.
@param NanoSeconds The minimum number of nanoseconds to delay.
@return The value of NanoSeconds inputted.
@ -107,23 +180,14 @@ NanoSecondDelay (
IN UINTN NanoSeconds
)
{
UINTN Index;
UINT32 MicroSeconds;
UINTN MicroSeconds;
// Round up to 1us Tick Number
MicroSeconds = (UINT32)NanoSeconds / 1000;
MicroSeconds += ((UINT32)NanoSeconds % 1000) == 0 ? 0 : 1;
MicroSeconds = NanoSeconds / 1000;
MicroSeconds += ((NanoSeconds % 1000) == 0) ? 0 : 1;
// Reload the counter for each 1Mhz to avoid an overflow in the load value
for (Index = 0; Index < (UINTN)PcdGet32(PcdSP804TimerFrequencyInMHz); Index++) {
// load the timer count register
MmioWrite32 (SP804_TIMER_METRONOME_BASE + SP804_TIMER_LOAD_REG, MicroSeconds);
MicroSecondDelay (MicroSeconds);
while (MmioRead32 (SP804_TIMER_METRONOME_BASE + SP804_TIMER_CURRENT_REG) > 0) {
;
}
}
return NanoSeconds;
}
@ -148,7 +212,6 @@ GetPerformanceCounter (
// Don't think we need this to boot, just to do performance profile
UINT64 Value;
Value = MmioRead32 (SP804_TIMER_PERFORMANCE_BASE + SP804_TIMER_CURRENT_REG);
ASSERT(Value > 0);
return Value;
}