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timer: fix corner case if counter is 0

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If counter drops to 0, the wrap flag is set also. That means we have actually
no wrap around. The patch avoids to add too much time to the elapsed time
variable.

Issue #1106
This commit is contained in:
Alexander Boettcher 2014-03-04 12:59:58 +01:00 committed by Christian Helmuth
parent 34a33e7301
commit 7d232cafb0
1 changed files with 18 additions and 11 deletions
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29
os/src/drivers/timer/include_pit/platform_timer.h
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@ -62,7 +62,7 @@ class Platform_timer
Genode::Io_port_connection _io_port;
Genode::Irq_connection _timer_irq;
unsigned long mutable _curr_time_usec;
unsigned long mutable _counter_init_value;
Genode::uint16_t mutable _counter_init_value;
Genode::Lock mutable _update_curr_time_lock;
bool mutable _handled_wrap;
@ -79,18 +79,18 @@ class Platform_timer
/**
* Read current PIT counter value
*/
unsigned long _read_counter(bool *wrapped)
Genode::uint16_t _read_counter(bool *wrapped)
{
/* read-back count and status of counter 0 */
_io_port.outb(PIT_CMD_PORT, PIT_CMD_READ_BACK |
PIT_CMD_RB_COUNT | PIT_CMD_RB_STATUS | PIT_CMD_RB_CHANNEL_0);
/* read status byte from latch register */
int status = _io_port.inb(PIT_DATA_PORT_0);
Genode::uint8_t status = _io_port.inb(PIT_DATA_PORT_0);
/* read low and high bytes from latch register */
int lo = _io_port.inb(PIT_DATA_PORT_0),
hi = _io_port.inb(PIT_DATA_PORT_0);
Genode::uint16_t lo = _io_port.inb(PIT_DATA_PORT_0);
Genode::uint16_t hi = _io_port.inb(PIT_DATA_PORT_0);
*wrapped = status & PIT_STAT_INT_LINE ? true : false;
return (hi << 8) | lo;
@ -124,7 +124,7 @@ class Platform_timer
{
Genode::Lock::Guard lock(_update_curr_time_lock);
unsigned long curr_counter, passed_ticks;
Genode::uint32_t passed_ticks;
/*
* Read PIT count and status
@ -134,15 +134,22 @@ class Platform_timer
* explicitly override the const-ness of the 'this' pointer.
*/
bool wrapped;
curr_counter = const_cast<Platform_timer *>(this)->_read_counter(&wrapped);
Genode::uint16_t const curr_counter = const_cast<Platform_timer *>(this)->_read_counter(&wrapped);
/* determine the time since we looked at the counter */
if (wrapped && !_handled_wrap) {
/* the counter wrapped from 0 to 0xffff */
passed_ticks = _counter_init_value + PIT_MAX_COUNT - curr_counter;
passed_ticks = _counter_init_value;
/* the counter really wrapped around */
if (curr_counter)
passed_ticks += PIT_MAX_COUNT + 1 - curr_counter;
_handled_wrap = true;
} else
passed_ticks = _counter_init_value - curr_counter;
} else {
if (_counter_init_value)
passed_ticks = _counter_init_value - curr_counter;
else
passed_ticks = PIT_MAX_COUNT + 1 - curr_counter;
}
_curr_time_usec += (passed_ticks*1000)/PIT_TICKS_PER_MSEC;