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MCS, ARM: Introduce TIMER_OVERHEAD_TICKS

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For ARM currently TIMER_PRECISION exists, but that is in microseconds
and not fine-grained enough.

This is needed to make periodic tasks synchronous with the system clock.
If this value is zero every period will be extended with the overhead of
taking an interrupt and reading the system clock. To avoid this drift,
the configured value should be set to at least the average overhead.

See also issue #844.

Signed-off-by: Indan Zupancic <Indan.Zupancic@mep-info.com>
This commit is contained in:
Indan Zupancic
2022-05-19 15:22:18 +02:00
committed by Kent McLeod
parent 3978092885
commit 4a7d08def0
6 changed files with 8 additions and 2 deletions
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1
.cmake-format.yaml
View File

@@ -52,5 +52,6 @@ additional_commands:
CLK_MAGIC: '*'
CLK_SHIFT: '*'
TIMER_PRECISION: '*'
TIMER_OVERHEAD_TICKS: '*'
MAX_SID: '*'
MAX_CB: '*'

3
config.cmake
View File

@@ -74,6 +74,9 @@ if(DEFINED CALLED_declare_default_headers)
if(NOT DEFINED CONFIGURE_TIMER_PRECISION)
set(CONFIGURE_TIMER_PRECISION "0")
endif()
if(NOT DEFINED CONFIGURE_TIMER_OVERHEAD_TICKS)
set(CONFIGURE_TIMER_OVERHEAD_TICKS "0")
endif()
configure_file(
src/arch/${KernelArch}/platform_gen.h.in
${CMAKE_CURRENT_BINARY_DIR}/gen_headers/plat/platform_gen.h @ONLY

2
configs/seL4Config.cmake
View File

@@ -118,7 +118,7 @@ macro(declare_default_headers)
cmake_parse_arguments(
CONFIGURE
""
"TIMER_FREQUENCY;MAX_IRQ;NUM_PPI;PLIC_MAX_NUM_INT;INTERRUPT_CONTROLLER;TIMER;SMMU;CLK_SHIFT;CLK_MAGIC;KERNEL_WCET;TIMER_PRECISION;MAX_SID;MAX_CB"
"TIMER_FREQUENCY;MAX_IRQ;NUM_PPI;PLIC_MAX_NUM_INT;INTERRUPT_CONTROLLER;TIMER;SMMU;CLK_SHIFT;CLK_MAGIC;KERNEL_WCET;TIMER_PRECISION;TIMER_OVERHEAD_TICKS;MAX_SID;MAX_CB"
""
${ARGN}
)

2
include/arch/arm/arch/machine/timer.h
View File

@@ -50,7 +50,7 @@ static inline CONST ticks_t usToTicks(time_t us)
static inline CONST ticks_t getTimerPrecision(void)
{
return usToTicks(TIMER_PRECISION);
return usToTicks(TIMER_PRECISION) + TIMER_OVERHEAD_TICKS;
}
#else /* CONFIG_KERNEL_MCS */
#include <mode/machine/timer.h>

1
src/arch/arm/platform_gen.h.in
View File

@@ -12,6 +12,7 @@
#define CLK_MAGIC @CONFIGURE_CLK_MAGIC@
#define CLK_SHIFT @CONFIGURE_CLK_SHIFT@
#define TIMER_PRECISION @CONFIGURE_TIMER_PRECISION@
#define TIMER_OVERHEAD_TICKS @CONFIGURE_TIMER_OVERHEAD_TICKS@
enum IRQConstants {
maxIRQ = @CONFIGURE_MAX_IRQ@

1
src/plat/tqma8xqp1gb/config.cmake
View File

@@ -22,6 +22,7 @@ if(KernelPlatformTqma8xqp1gb)
TIMER_FREQUENCY 8000000
MAX_IRQ 512
TIMER drivers/timer/arm_generic.h
TIMER_OVERHEAD_TICKS 1
INTERRUPT_CONTROLLER arch/machine/gic_v3.h
NUM_PPI 32
CLK_MAGIC 1llu