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Add documentation for the cyclic function infrastructure, including the cyclic command. Signed-off-by: Stefan Roese <sr@denx.de> Reviewed-by: Simon Glass <sjg@chromium.org>
50 lines
1.8 KiB
ReStructuredText
50 lines
1.8 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0+
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Cyclic functions
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================
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The cyclic function execution infrastruture provides a way to periodically
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execute code, e.g. every 100ms. Examples for such functions might be LED
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blinking etc. The functions that are hooked into this cyclic list should
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be small timewise as otherwise the execution of the other code that relies
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on a high frequent polling (e.g. UART rx char ready check) might be
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delayed too much. To detect cyclic functions with a too long execution
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time, the Kconfig option `CONFIG_CYCLIC_MAX_CPU_TIME_US` is introduced,
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which configures the max allowed time for such a cyclic function. If it's
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execution time exceeds this time, this cyclic function will get removed
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from the cyclic list.
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Registering a cyclic function
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-----------------------------
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To register a cyclic function, use something like this::
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static void cyclic_demo(void *ctx)
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{
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/* Just a small dummy delay here */
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udelay(10);
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}
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int board_init(void)
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{
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struct cyclic_info *cyclic;
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/* Register demo cyclic function */
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cyclic = cyclic_register(cyclic_demo, 10 * 1000, "cyclic_demo", NULL);
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if (!cyclic)
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printf("Registering of cyclic_demo failed\n");
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return 0;
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}
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This will register the function `cyclic_demo()` to be periodically
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executed all 10ms.
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How is this cyclic functionality integrated / executed?
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--------------------------------------------------------
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The cyclic infrastructure integrates the main function responsible for
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calling all registered cyclic functions cyclic_run() into the common
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WATCHDOG_RESET macro. This guarantees that cyclic_run() is executed
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very often, which is necessary for the cyclic functions to get scheduled
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and executed at their configured periods.
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