BSP Hot Swap

The ChorusOS Board Support Package (BSP) hot swap feature allows you to remove and replace a board from an instance of the ChorusOS operating system, without having to shut the system down. BSP hot swap starts and stops the driver corresponding to a board that is inserted or removed.

The BSP hot swap features a two-layer implementation:

• A board-dependent layer, the Hot Swap Controller (HSC), that handles the ENUM# signal. The ENUM# signal notifies the system of an insertion or a removal event specified by Peripheral Component Interconnect (PCI) hot swap.

• A common layer that implements the handler attached to the ENUM# signal. This is a PciSwap device driver installed between the bridge-specific PCI bus implementation and the implementation of the board-specific HSC hot swap interrupt driver.

Hot Swap Support

ChorusOS BSP hot swap support defines and implements a common layer between the PCI bus device driver and the HSC device driver. The implementation of the PCI bus (bridge) is chip-specific and is not supposed to be aware of the PCI hot swap capabilities. However, the handling of the ENUM# event is board-specific, because the ENUM# signal can be routed to any interrupt source and can even be polled upon timeout. The detection of this is not parent bus-specific either, but depends on the implementation of the PCI device inserted.

BSP Hot Swap support is split into three stages:

• Handling the ENUM# signal.

• Accessing the Hot Swap Control/Status Register (HS_CSR)

• Interconnecting with the System Management (system event propagation).

Compact PCI-type devices and the dec2115x bridge family are supported.

Hot Swap Sequences

The BSP hot swap feature of the ChorusOS operating system performs the following operations upon system start-up and the insertion or removal of a board.

Start up

When started, the PciSwap device driver looks up the device registry for the HSC device driver specified for its node. If found, the PciSwap driver opens the HSC device and installs its ENUM# handler. Without an ENUM# handler the PCI bus node will not support hot swap. The PCI bus driver init-method looks up the device registry and searches for the instance of the PciSwap driver specified for its device node. If found, the PCI bus driver opens the connection to this instance and installs its handlers for insertion and removal events. The PCI bus node now has hot swap capabilities.

Insertion of a Board

On insertion of a board, the ENUM# signal is detected and neutralized by the HSC device driver. This event is passed to the PciSwap driver, which detects the slot into which the board is inserted. The parent PCI bus driver is notified for each insertion. The PCI bus driver or PciSwap (or both) invokes the PCI enumerator. New device nodes are created or static nodes are activated. The device-specific driver establishes the connection to the PCI bus. The PCI bus driver invokes a lock method for each activated device node in the PciSwap driver. The slot is declared BUSY.

Removal of a Board

The ENUM# signal is detected by the HSC device driver. This event is passed to the PciSwap driver, which detects which slot to remove. The parent PCI bus driver is notified for each removal. The PCI bus driver sends the device shutdown event. The PCI device closes its connection to the PCI bus. The PCI bus driver or PciSwap (or both) invokes the PCI enumerator. The dynamic (enumerated) device nodes are deleted or static nodes are deactivated. When the last connection to the PCI bus driver for the slot is closed, the PCI bus driver invokes the method of the PciSwap driver. The slot is declared FREE and can be removed.

BSP Hot Swap API

The BSP hot swap feature API is given in the table below:

Function	Description
open()	Establish a connection between PCI bus and the Hot Swap Controller device.
lock()	Called before device initialization, to show that the PCI slot is busy.
unlock()	Called after device shut down, to show that the PCI slot is free to extract.
close()	Close a connection between PCI bus and the Hot Swap Controller device.