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doc: optimize deep_sleep_wake_stub README

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wuzhenghui 2023-03-13 13:31:38 +08:00
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examples/system/deep_sleep_wake_stub/README.md
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@ -13,7 +13,7 @@ In this example, the `CONFIG_BOOTLOADER_SKIP_VALIDATE_IN_DEEP_SLEEP` Kconfig opt
### Hardware Required ### Hardware Required
This example should be able to run on any commonly available ESP32/ESP32-S2/ESP32-S3/ESP32-C3/ESP32-C6 development board without any extra hardware if only **Timer** wake up sources are used. This example runs on any commonly available development board with a chip listed under "Supported Targets" without requiring any extra hardware if only **Timer** wake up sources are used.
### Configure the project ### Configure the project
@ -77,8 +77,8 @@ wake stub: going to deep sleep
> Note: > Note:
> 1. The wakeup time cost printed in this example is not accurate, it does not take into account the hardware initialization time before the CPU starts, for most esp chips the initialization time cost is about 280us. > 1. The wakeup time cost printed in this example is not entirely accurate. This is because it does not take into account the hardware initialization time before the CPU starts. For most ESP chips, the initialization time is about 280 us.
> 2. And the wake-up time shown in this example is not the optimal wake-up time, because the ROM printing before the wake stub occupies most of the wake-up time, for most esp chips this ROM printing takes about 6100us. In the product firmware, users can temporarily or permanently turn off ROM printing via call `esp_deep_sleep_disable_rom_logging` or set `menuconfig->Boot ROM Behavior->Permanently disable logging` to speed up the wake-up time. > 2. The wake-up time shown in this example may be reduced by disabling the logs printed by ROM code. For most ESP chips, this ROM printing takes about 6100 us. In the product firmware, users can temporarily or permanently turn off ROM printing by calling ``esp_deep_sleep_disable_rom_logging`` or by setting ``menuconfig`` > ``Boot ROM Behavior`` > ``Permanently disable logging`` to speed up the wake-up.(ESP32 does not support suppressing ROM logging through menuconfig, but it can be suppressed by grounding GPIO15)
> 3. A method for roughly estimating optimal wake-up time: Taking esp32c6 as example, the wake-up time from stub printing is about 6500us, minus the ROM printing overhead of 6100us, plus the system initialization overhead of 280us, its optimal wake-up overhead is about 680us. Users also can modify the example to configure GPIO wake-up, and obtain a more realistic and accurate wake-up time by grabbing GPIO signals > 3. Here is a method for roughly estimating optimal wake-up time: Taking ESP32-C6 as an example, the wake-up time from stub printing is about 6500 us. However, by substracting the ROM printing overhead of 6100 us and adding the system initialization overhead of 280 us, the wake-up overhead is estimated to be around 680 us. Users also can modify the example to configure GPIO wake-up and obtain a more realistic and accurate wake-up time by grabbing GPIO signals with a logic analyzer.