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base-hw: fix EPIT duration calculation on roll-over

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If Ocif was not reset between two calls to _duration(), the returned
value exceeded _max_value().
This commit is contained in:
Christian Helmuth 2024-03-14 16:49:46 +01:00
parent abb2045e17
commit 2f1520b4c1
2 changed files with 3 additions and 12 deletions
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14
repos/base-hw/src/core/spec/arm/imx_epit.cc
View File

@ -54,6 +54,7 @@ void Board::Timer::init()
Cr::access_t cr = read<Cr>();
Cr::En_mod::set(cr, Cr::En_mod::RELOAD);
Cr::Oci_en::set(cr, 1);
Cr::Rld::set(cr, 0);
Cr::Prescaler::set(cr, Cr::Prescaler::DIVIDE_BY_1);
Cr::Clk_src::set(cr, Cr::Clk_src::HIGH_FREQ_REF_CLK);
Cr::Iovw::set(cr, 1);
@ -97,19 +98,8 @@ time_t Timer::_duration() const
Device::Cnt::access_t const initial_cnt {
(Device::Cnt::access_t)_last_timeout_duration };
/*
* There are two situations here:
*
* 1. SR.OCIF reads as 1, meaning, the timer IRQ has triggered. In
* this case we read CNT after having read SR.OCIF in order to
* ensure that we use a post-IRQ (wrapped) counter value.
*
* 2. SR.OCIF reads as 0, meaning, the timer IRQ hasn't triggered yet. In
* this case we read CNT before having read SR.OCIF in order to
* ensure that we use a pre-IRQ (non-wrapped) counter value.
*/
Device::Cnt::access_t const curr_cnt { _device.read<Device::Cnt>() };
if (_device.read<Device::Sr::Ocif>())
if (curr_cnt > initial_cnt)
return _max_value() - _device.read<Device::Cnt>() + initial_cnt;
else
return initial_cnt - curr_cnt;

1
repos/base-hw/src/core/spec/arm/imx_epit.h
View File

@ -40,6 +40,7 @@ struct Board::Timer : Genode::Mmio<0x14>
};
struct Oci_en : Bitfield<2, 1> { }; /* interrupt on compare */
struct Rld : Bitfield<3, 1> { }; /* counter reload mode */
struct Prescaler : Bitfield<4, 12> /* clock input divisor */
{