Update README files
This commit is contained in:
Gregory Nutt
parent
fb152aa037
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@ -77,6 +77,7 @@ Contents
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- RTC
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- Watchdog Timer
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- TRNG and /dev/random
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- Tickless OS
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- I2S Audio Support
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- SAMA5D3-Xplained Configuration Options
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- Configurations
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@ -2328,6 +2329,62 @@ TRNG and /dev/random
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CONFIG_EXAMPLES_MAXSAMPLES=64 : Default settings are probably OK
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CONFIG_EXAMPLES_NSAMPLES=8
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Tickless OS
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===========
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By default, a NuttX configuration uses a periodic timer interrupt that
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drives all system timing. The timer is provided by architecture-specifi
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code that calls into NuttX at a rate controlled by CONFIG_USEC_PER_TICK.
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The default value of CONFIG_USEC_PER_TICK is 10000 microseconds which
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corresponds to a timer interrupt rate of 100 Hz.
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An option is to configure NuttX to operation in a "tickless" mode. Some
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limitations of default system timer are, in increasing order of
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importance:
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- Overhead: Although the CPU usage of the system timer interrupt at 100Hz
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is really very low, it is still mostly wasted processing time. One most
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timer interrupts, there is really nothing that needs be done other than
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incrementing the counter.
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- Resolution: Resolution of all system timing is also determined by
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CONFIG_USEC_PER_TICK. So nothing that be time with resolution finer than
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10 milliseconds be default. To increase this resolution,
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CONFIG_USEC_PER_TICK an be reduced. However, then the system timer
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interrupts use more of the CPU bandwidth processing useless interrupts.
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- Power Usage: But the biggest issue is power usage. When the system is
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IDLE, it enters a light, low-power mode (for ARMs, this mode is entered
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with the wfi or wfe instructions for example). But each interrupt
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awakens the system from this low power mode. Therefore, higher rates
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of interrupts cause greater power consumption.
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The so-called Tickless OS provides one solution to issue. The basic
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concept here is that the periodic, timer interrupt is eliminated and
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replaced with a one-shot, interval timer. It becomes event driven
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instead of polled: The default system timer is a polled design. On
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each interrupt, the NuttX logic checks if it needs to do anything
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and, if so, it does it.
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Using an interval timer, one can anticipate when the next interesting
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OS event will occur, program the interval time and wait for it to fire.
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When the interval time fires, then the scheduled activity is performed.
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The following configuration options will enable support for the Tickless
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OS for the SAMA5D platforms using TC0 channels 0-3 (other timers or
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timer channels could be used making the obvious substitutions):
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RTOS Features -> Clocks and Timers
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CONFIG_SCHED_TICKLESS=y : Configures the RTOS in tickless mode
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System Type -> SAMA5 Peripheral Support
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CONFIG_SAMA5_TC0=y : Enable TC0 (TC channels 0-3
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System Type -> Timer/counter Configuration
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CONFIG_SAMA5_ONESHOT=y : Enables one-shot timer wrapper
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CONFIG_SAMA5_FREERUN=y : Enabled free-running timer wrapper
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CONFIG_SAMA5_TICKLESS_ONESHOT=0 : Selects TC0 channel 0 for the one-shot
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CONFIG_SAMA5_TICKLESS_FREERUN=1 : Selects TC0 channel 1 for the free-
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: running timer
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I2S Audio Support
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=================
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@ -91,6 +91,7 @@ Contents
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- Watchdog Timer
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- TRNG and /dev/random
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- Touchscreen Testing
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- Tickless OS
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- OV2640 Camera Interface
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- I2S Audio Support
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- SAMA5D3x-EK Configuration Options
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@ -2644,6 +2645,62 @@ Touchscreen Testing
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Defaults should be okay for all related settings.
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Tickless OS
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===========
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By default, a NuttX configuration uses a periodic timer interrupt that
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drives all system timing. The timer is provided by architecture-specifi
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code that calls into NuttX at a rate controlled by CONFIG_USEC_PER_TICK.
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The default value of CONFIG_USEC_PER_TICK is 10000 microseconds which
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corresponds to a timer interrupt rate of 100 Hz.
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An option is to configure NuttX to operation in a "tickless" mode. Some
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limitations of default system timer are, in increasing order of
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importance:
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- Overhead: Although the CPU usage of the system timer interrupt at 100Hz
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is really very low, it is still mostly wasted processing time. One most
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timer interrupts, there is really nothing that needs be done other than
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incrementing the counter.
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- Resolution: Resolution of all system timing is also determined by
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CONFIG_USEC_PER_TICK. So nothing that be time with resolution finer than
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10 milliseconds be default. To increase this resolution,
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CONFIG_USEC_PER_TICK an be reduced. However, then the system timer
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interrupts use more of the CPU bandwidth processing useless interrupts.
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- Power Usage: But the biggest issue is power usage. When the system is
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IDLE, it enters a light, low-power mode (for ARMs, this mode is entered
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with the wfi or wfe instructions for example). But each interrupt
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awakens the system from this low power mode. Therefore, higher rates
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of interrupts cause greater power consumption.
|
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The so-called Tickless OS provides one solution to issue. The basic
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concept here is that the periodic, timer interrupt is eliminated and
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replaced with a one-shot, interval timer. It becomes event driven
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instead of polled: The default system timer is a polled design. On
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each interrupt, the NuttX logic checks if it needs to do anything
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and, if so, it does it.
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Using an interval timer, one can anticipate when the next interesting
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OS event will occur, program the interval time and wait for it to fire.
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When the interval time fires, then the scheduled activity is performed.
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The following configuration options will enable support for the Tickless
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OS for the SAMA5D platforms using TC0 channels 0-3 (other timers or
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timer channels could be used making the obvious substitutions):
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RTOS Features -> Clocks and Timers
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CONFIG_SCHED_TICKLESS=y : Configures the RTOS in tickless mode
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System Type -> SAMA5 Peripheral Support
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CONFIG_SAMA5_TC0=y : Enable TC0 (TC channels 0-3
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System Type -> Timer/counter Configuration
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CONFIG_SAMA5_ONESHOT=y : Enables one-shot timer wrapper
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CONFIG_SAMA5_FREERUN=y : Enabled free-running timer wrapper
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CONFIG_SAMA5_TICKLESS_ONESHOT=0 : Selects TC0 channel 0 for the one-shot
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CONFIG_SAMA5_TICKLESS_FREERUN=1 : Selects TC0 channel 1 for the free-
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: running timer
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OV2640 Camera Interface
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=======================
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@ -94,6 +94,7 @@ Contents
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- TRNG and /dev/random
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- Audio Support
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- TM7000 LCD/Touchscreen
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- Tickless OS
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- SAMA4D4-EK Configuration Options
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- Configurations
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- To-Do List
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@ -3108,6 +3109,62 @@ TM7000 LCD/Touchscreen
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---
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To be provided.
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Tickless OS
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===========
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By default, a NuttX configuration uses a periodic timer interrupt that
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drives all system timing. The timer is provided by architecture-specifi
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code that calls into NuttX at a rate controlled by CONFIG_USEC_PER_TICK.
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The default value of CONFIG_USEC_PER_TICK is 10000 microseconds which
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corresponds to a timer interrupt rate of 100 Hz.
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An option is to configure NuttX to operation in a "tickless" mode. Some
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limitations of default system timer are, in increasing order of
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importance:
|
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- Overhead: Although the CPU usage of the system timer interrupt at 100Hz
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is really very low, it is still mostly wasted processing time. One most
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timer interrupts, there is really nothing that needs be done other than
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incrementing the counter.
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- Resolution: Resolution of all system timing is also determined by
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CONFIG_USEC_PER_TICK. So nothing that be time with resolution finer than
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10 milliseconds be default. To increase this resolution,
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CONFIG_USEC_PER_TICK an be reduced. However, then the system timer
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interrupts use more of the CPU bandwidth processing useless interrupts.
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- Power Usage: But the biggest issue is power usage. When the system is
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IDLE, it enters a light, low-power mode (for ARMs, this mode is entered
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with the wfi or wfe instructions for example). But each interrupt
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awakens the system from this low power mode. Therefore, higher rates
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of interrupts cause greater power consumption.
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The so-called Tickless OS provides one solution to issue. The basic
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concept here is that the periodic, timer interrupt is eliminated and
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replaced with a one-shot, interval timer. It becomes event driven
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instead of polled: The default system timer is a polled design. On
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each interrupt, the NuttX logic checks if it needs to do anything
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and, if so, it does it.
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Using an interval timer, one can anticipate when the next interesting
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OS event will occur, program the interval time and wait for it to fire.
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When the interval time fires, then the scheduled activity is performed.
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The following configuration options will enable support for the Tickless
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OS for the SAMA5D platforms using TC0 channels 0-3 (other timers or
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timer channels could be used making the obvious substitutions):
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RTOS Features -> Clocks and Timers
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CONFIG_SCHED_TICKLESS=y : Configures the RTOS in tickless mode
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System Type -> SAMA5 Peripheral Support
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CONFIG_SAMA5_TC0=y : Enable TC0 (TC channels 0-3
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System Type -> Timer/counter Configuration
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CONFIG_SAMA5_ONESHOT=y : Enables one-shot timer wrapper
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CONFIG_SAMA5_FREERUN=y : Enabled free-running timer wrapper
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CONFIG_SAMA5_TICKLESS_ONESHOT=0 : Selects TC0 channel 0 for the one-shot
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CONFIG_SAMA5_TICKLESS_FREERUN=1 : Selects TC0 channel 1 for the free-
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: running timer
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SAMA4D4-EK Configuration Options
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=================================
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