Add information on power saving options for USB components #1154
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hugueskamba
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AnotherButler and
evedon
docs/api/usb/usb_component.md
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| ## USB component and power saving | ||
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| Instantiated USB components prevent devices from going to deep sleep due to USBPhy holding a deep sleep lock. It is possible to temporarily disable USB using `USBDevice::deinit()` to permit deep sleep. However, it is up to the user to make sure all the data transfers have concluded (for example when USB power is lost) to avoid any data corruption. The USB host controls the enumeration process so it chooses when and how the device will be restored. Even if the device state is returned to what it was before the disconnect, the host PC software may not be where it left off - for example a serial port may need to be re-opended by the user. |
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(for example when USB power is lost) i'm not sure I follow what does this mean, you mean it's a similar situation hen usb power is lost?
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| Instantiated USB components prevent devices from going to deep sleep because USBPhy holds a deep sleep lock. You can temporarily disable USB using `USBDevice::deinit()` to permit deep sleep. However, you must make sure all the data transfers have concluded to avoid any data corruption. The USB host controls the enumeration process, so it chooses when and how to restore the device. Even if the device state is returned to what it was before the disconnect, the host PC software may not be where it left off - for example, you may need to reopen a serial port. | ||
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| You can use `USBDevice::connect()` to resume USB component operation when USB power is detected after it was previously suspended through `USBDevice::deinit()`. |
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Could you suggest a way to rephrase this sentence? I had to read it a few times for it to make sense.
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I do not mind your edit if it removes the confusion.
@AnotherButler |
docs/api/usb/usb_component.md
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| ## USB component and power saving | ||
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| Instantiated USB components prevent devices from going to deep sleep because USBPhy holds a deep sleep lock. You can temporarily disable USB using `USBDevice::deinit()` to permit deep sleep. However, you must make sure all the data transfers have concluded to avoid any data corruption. The USB host controls the enumeration process, so it chooses when and how to restore the device. Even if the device state is returned to what it was before the disconnect, the host PC software may not be where it left off - for example, you may need to reopen a serial port. |
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Instantiated USB components prevent devices from going to deep sleep because USBPhy holds a deep sleep lock.
Note - this is implementation defined. Nothing requires a USBPhy to lock deep sleep, all implementations currently do though.
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Actually not all implementations do, the Cypress one does not.
https://github.com/ARMmbed/mbed-os/blob/master/targets/TARGET_Cypress/TARGET_PSOC6/cy_usb_phy.cpp#L57
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This PR fixes the Cypress USBPhy.
Edit file, mostly for active voice.
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Apply changes from PR #1154 to v5.14.
Related to: ARMmbed/mbed-os#11635