Card Removal and Insertion Procedures
The descriptions of typical card removal and insertion that follow are intended to be introductory in nature. Additional detail can be found later in this chapter.
It should be noted that the procedures described in the following sections assume that the OS, rather than the Hot-Plug System Driver, is responsible for configuring a newly-installed device. If the Hot-Plug System Driver has this responsibility, the Hot-Plug Service will call the Hot-Plug System Driver and instruct it to configure the newly-installed device.
On and Off States
Definition of On and Off
A slot in the On state has the following characteristics:
Power is applied to the slot. REFCLK is on. The link is active or in the standby (L0s or L1 ) low power state due to Active State Power Management. The PERST# signal is deasserted.
A slot in the Off state has the following characteristics:
Power to the slot is turned off. REFCLK is off. The link is inactive. (Driver at the root of switch port is in Hi Z state) The PERST# signal is asserted.
Turning Slot Off
Steps required to turn off a slot that is currently in the On state:
Deactivate the link. This may involve issuing a Electrical Idle ordered set (a sequence initiated at the Physical Layer that forces the Card's driver to enter the Hi Z state. Assert the PERST# signal to the slot. Turn off REFCLK to the slot. Remove power from the slot.
Turning Slot On
Steps to turn on a slot that is currently in the off state:
Apply power to the slot. Turn on REFCLK to the slot Deassert the PERST# signal to the slot. The system must meet the setup and hold timing requirements (specified in the PCI Express spec) relative to the rising edge of PERST#.
Once power and clock have been restored and PERST# removed, the physical layers at both ports will perform link training and initialization. When the link is active, the devices will initialize VC0 (including flow control), making the link ready to transfer TLPs.
Card Removal Procedure
When a card must be removed, a number of steps must occur to not only prepare software and hardware for safe removal of the card, but also to control indicators that provide visual evidence of the request to remove the card being processed. The condition of the indicators during normal operation are:
Software issues "Requests" to the Hot Plug Controller via configuration write transactions that target the "Slot Control Registers implemented by Hot-Plug capable ports." These requests control power to the slot and the state of the indicators.
The exact sequence of events that occur when performing a Hot Plug card removal vary slightly depending on whether the Hot Plug operation is initiated by pressing the Attention Button or via the User Interface software utility. Each sequence is described below.
Attention Button Used to Initiate Hot Plug Removal
The sequence of events is as follows:
The operator initiates the card removal request by depressing the slot's "attention button." The Hot-Plug Controller detects this event and delivers an interrupt to the root complex. As a result of the interrupt the Hot Plug service calls the Hot Plug System Driver, which reads slot status information and detects the Attention Button request. Next, the Hot-Plug Service issues a request to the Hot-Plug System Driver commanding the Hot Plug Controller to blink the slot's Power Indicator. The operator is granted a 5 second abort interval, from the time that the indicators starts to blink, during which the operator may press the button a second time to abort the request. The Power Indicator continues to blink while the Hot Plug software validates the request. Note that software may fail to validate the request (e.g., the card may currently be used for some critical system operation). If the request is validated, the Hot-Plug Service utility commands the card's device driver to quiesce. That is, the driver must stop issuing requests to the card and complete or terminate all outstanding requests as well as disable its ability to generate transactions (including interrupt messages). Software then issues a command to disable the card's link via the Link Control register within the root or switch port to which the slot is attached. This causes ports at both ends of the link to be disabled. Next, software commands the Hot Plug Controller to turn the slot off. Following successful power down software issues the Power Indicator Off Request. The operator knows that the card may be removed safely from the slot when the Power Indicator is Off. The operator releases the Mechanical Retention Latch, causing the Hot Plug Controller to remove all switched signals from the slot (e.g., SMBus and JTAG signals). The card can now be removed. The OS deallocates the memory space, IO space, interrupt line, etc. that had been assigned to the device and makes these resources available for assignment to other devices in the future.
Hot Plug Removal Request Issued via User Interface
The sequence of events is as follows:
The operator initiates the card removal request by selecting the Physical Slot number associated with the card to be removed. Software opens a window or presents a message requesting the operator confirm the request. Note that the Power Indicator remains on during this process. When the operator confirms the request, the Hot-Plug Service issues a request to the Hot-Plug System Driver commanding the Hot Plug Controller to blink the slot's Power Indicator. During this time, software validates the Hot Plug request. Note that software may fail to validate the request (e.g., the card may currently being used for some critical system operation). If the request is validated, the Hot-Plug Service utility commands the card's device driver to quiesce. That is, the driver must stop issuing requests to the card and complete or terminate all outstanding requests as well as disable its ability to generate transactions (including interrupt messages). Software then issues a command to disable the card's link via the Link Control register located in the root or switch port to which the slot connects. This causes ports at both ends of the link to be disabled. Next, software commands the Hot Plug Controller to disable the slot. Following successful power down software issues the Power Indicator Off Request. The operator knows that the card may be removed safely from the slot when the Power Indicator is Off. The operator releases the Manual Retention Latch (MRL), causing the Hot Plug Controller to remove all switched signals from the slot (e.g., SMBus and Vaux signals). The card can now be removed. The OS deallocates the memory space, IO space, interrupt line, etc. that had been assigned to the device and makes these resources available for assignment to other devices in the future.
Card Insertion Procedure
The procedure for installing a new card basically reverses the steps listed for card removal. The following steps assume that the card slot was left in the same state that it was in immediately after a card was removed from the connector (in other words, the Power Indicator is in the Off state, indicating the slot is ready for card insertion). Variations between the two methods of initiation are described below.
Card Insertion Initiated by Pressing Attention Button
The steps taken to Insert and enable a card are as follows:
The operator installs the card and secures the MRL. If implemented, the MRL sensor will signal the Hot-Plug Controller that the latch is closed, causing switched auxillary signals and Vaux to be connected to the slot. Next, the operator notifies the Hot-Plug Service that the card has been installed by pressing the Attention Button. This signals the Hot Plug controller of the event, resulting in status register bits being set and causing a system interrupt to be sent to the Root Complex. Subsequently, Hot Plug software reads slot status from the port and recognizes the request. The Hot-Plug Service issues a request to the Hot-Plug System Driver commanding the Hot Plug Controller to blink the slot's Power Indicator to inform the operator that the card must not be removed. The operator is granted a 5 second abort interval, from the time that the indicators starts to blink, to abort the request by pressing the button a second time. The Power Indicator continues to blink while Hot Plug software validates the request. Note that software may fail to validate the request (e.g., the security policy settings may prohibit the slot being enabled). The Hot-Plug Service issues a request to the Hot-Plug System Driver commanding the Hot Plug Controller to turn the slot on. Once power is applied, software issues a command to turn the Power Indicator ON. Once link training is complete, the OS commands the Platform Configuration Routine to configure the card function(s) by assigning the necessary resources. The OS locates the appropriate driver(s) (using the Vendor ID and Device ID, or the Class Code, or the Subsystem Vendor ID and Subsystem ID configuration register values as search criteria) for the function(s) within the PCI Express device and loads it (or them) into memory. The OS then calls the driver's initialization code entry point, causing the processor to execute the driver's initialization code. This code finishes the setup of the device and then sets the appropriate bits in the device's PCI configuration Command register to enable the device.
Card Insertion Initiated by User Interface
The steps taken to Re-enable the card are as follows:
The operator installs the card and secures the MRL. The MRL sensor signals the Hot Plug Controller to connect the switched signals to the slot. Next, the operator informs the Hot-Plug Service (via the Hot Plug Utility program) that the card has been installed and is ready to be re-enabled. Software then prompts the user to verify that it is safe to re-enable the slot. After the operator requests card insertion, the Hot-Plug Service issues a request to the Hot-Plug System Driver commanding the Hot Plug Controller to blink the slot's Power Indicator to inform the operator that the card must not be removed. The Power Indicator continues to blink while Hot Plug software validates the request. Note that software may fail to validate the request (e.g., the security policy settings may be prohibit the slot being enabled). The Hot-Plug Service issues a request to the Hot-Plug System Driver commanding the Hot Plug Controller to reapply power to the slot. Once power is applied, software issues a command to turn the Power Indicator ON. Once link training is complete, the OS commands the Platform Configuration Routine to configure the card function(s) by assigning the necessary resources. The OS locates the appropriate driver(s) (using the Vendor ID and Device ID, or the Class Code, or the Subsystem Vendor ID and Subsystem ID configuration register values as search criteria) for the function(s) within the PCI Express device and loads it (or them) into memory. The OS then calls the driver's initialization code entry point, causing the processor to execute the driver's initialization code. This code finishes the setup of the device and then sets the appropriate bits in the device's PCI configuration Command register to enable the device.
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