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### NVME SSD Power Control Manager
#### Description
The package mantains for SSD power control and related noification handle Deamon
#### Design
The service power supply design follow PCI Express Card Electromechanical Specification Revision 3.0 in Section 2.2
nvme_gpio.service follow section 2.2.1 Initial power-Up to initinal and adjust related signal.
nvme_powermanager.service follow section 2.2.2 power management states monitor PRESENT signal and update related signal.
#### Process
* Plugging
1. U2_[SSD_index] PRSNT_N will be input low
2. Set PWR_U2_[SSD_index]_EN to high
3. Check PWRGD_U2_[SSD_index] is high
4-1. If PWRGD_U2_[SSD_index] is high (PWR Good)
- Wait 5ms
- Enable PCI Clock by SMBus 9FGL0851
- Wait 100ms
- Set RST_BMC_U2 to high
4-2. If PWRGD_U2_[SSD_index] is low (PWR Fail)
- Set RST_BMC_U2_[SSD_index]_R_N to low
- Wait 100ms
- Disable PCI Clock by SMBus
* Removing
1. U2_[SSD_index] PRSNT_N will be input high
2. Set RST_BMC_U2 to low
3. Wait 100ms
4. Disable PCI Clock by SMBus
5. Wait 5ms
6. PWR_U2_[SSD_index]_EN to low
#### Test
1. PRESENT detect SSD: The hardware design has been implemented.
2. Initial SSD slot Power output: nvme_gpio service has tested on Module. It could sucess initial gpios and set correct power output.
3. Detect PRESENT and change power setting: nvme_powermanager service has tested on Module. It could success detect SSD plugged or removal change power output.
4. Improve initial power-up sequence: For matched hardware default initial power-up setting, the nvme_gpio service only set unplugged slot related signal.
5. Improve service execute sequence: nvme_powermanager.service must wait for nvme_gpio.service ensure gpio export complete.
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