There are three distinct types of
Conventional Reset and each of these causes the hardware state machines, hardware
logic, port states and configuration registers to be initialized to their default
values.
- Cold Reset – The reset
occurring at power-up of the device is referred to as Cold Reset. Cold Reset
is triggered by the PERSTn signal being asserted. PERSTn signal is an
auxiliary signal in PCIе Specification and can be used at power on reset for
the device that has PCIe as its primary bus interface to rest of the system.
The device is allowed to generate its own power-on reset as long as the PCIe
requirements for PERSTn are met. See PCIe Base Specifications for
details.
- Warm Reset – A reset can be
triggered by the hardware without the removal of power from the device. This
reset is referred to as Warm Reset. The hardware implementation is not
specified by the PCIе Specification.
- Hot Reset – The PCIе
Specifications provides an in-band mechanism to propagate a Conventional
Reset across a Link. This reset, called the Hot Reset, propagates via the
transmission of TS1 Ordered Sets. In general, Hot Reset is software
controlled procedure and can only be issued by
Root
Complex in a PCIе network as the propagation is downstream
only. PCIe subsystem translates the received in-band hot reset into an
interrupt that can then be used by software to reset the PCIe
subsystem.
After a conventional reset, the
software must wait at least 100 ms before attempting any PCIe transaction on the
device that has been reset. If the downstream device does not respond to transaction
packets, it must not give up until 1 second plus an additional 50% (0.5 second) time
is lapsed.