Answers Database
LogiCORE PCI: Implementing CompactPCI HotSwap with Xilinx LogiCORE PCI solution
Record #5261
Product Family: Documentation
Product Line: PCI Apps
Product Part: PCI Frequently Asked Questions
Problem Title:
LogiCORE PCI: Implementing CompactPCI HotSwap with Xilinx LogiCORE PCI solution
Problem Description:
Urgency: Standard
General Description:
Implementing CompactPCI HotSwap with Xilinx LogiCORE PCI solution
Solution 1:
Hot Swap is a extension of the CompactPCI specification that
allows the removal and insertion of cards without removing
power from the bus. This is of great interest to the telecom
and networking industries because it will allow implementation
of High Availability systems, where repairs and upgrades can be
done without downtime.
Hot Swap should not be confused with Hot Plug, a PCI
initiative. Hot Plug is only for the regular PCI form factor
and requires powering down the slot. Hot Swap does not require
the slot to be powered down.
Solution 2:
Using Xilinx PCI for Hot Swap:
The Hot Swap Specification defines three levels of compliance
for the silicon:
Hot Swap Capable. The minimum level of compliance to operate in
a Hot Swap environment; devices must be PCI V2.1 compliant and
meet several additional electrical requirements.
Hot Swap Friendly is the next level of compliance above
Capable. It includes all the specifications for Capable and
adds the support for the Extended Capability Pointer and the
Hot Swap Control and Status Register. This register is accessed
through the Extended Capabilities pointer. See the PCI V2.2
Specification for more details on this pointer.
Hot Swap Ready. The highest level of compliance. Includes Hot
Swap Friendly and internal Bias Voltage support and Early power
support.
The XC4000XLT and Spartan Devices -
These FPGA families have default pull-ups on I/Os before and
during configuration. This causes a leakage current that will
exceed the Hot Swap Specification of 10 uA. After
configuration, the resistors are eliminated by the bitstream,
but configuration may take longer than the insertion process.
As the CompactPCI card is inserted, the time between the early
power pins and the signal pins can be as short as 4mS, which is
less than the time required for configuration. There are two
possible solutions to this leakage current.
1. Use the device in a leakage test mode. The 4000E, XL, XLT,
and XLA devices have a leakage test mode that eliminates the
pull-up resistors. The Spartan-XL (but not the Spartan) family
has a low power mode that elimi-nates the pull-ups. This will
meet the requirements of the Hot Swap Insertion. However, once
insertion has been completed, the device must be put into a
regular configuration; the pull-ups will return until the end
of configuration. The PCI V2.1 Specification calls for no more
than 70 uA leakage current. This may cause a vio-lation of the
V2.1 PCI specification for the length of the configuration.
- For 4000E, XLT, and XLA devices, use the leakage test mode.
The leakage test mode can be accessed by setting the mode
pins to M2=0, M1=0 M0=1, and PGM=0.
Note: For the 4KXLA parts in leakage test mode, an N-well transistor
in the IO will turn on if the transistor's threshold voltage is reached.
Once this N-well transistor turns on, it will form a feedback circuit and
the IO will get stuck. When in this mode, a strong pullup or pulldown
is required to pull the IO out of the feedback loop. The threshold
voltage to turn on the transistor depends on Vcc. At a Vcc of 3.3V,
the threshold voltage is aproximately 2.3V.
- For Spartan-XL devices, use the Low Power mode. The low power
mode can be accessed by setting M2=0.
- Spartan devices do not have a user accessible test mode.
In both cases after insertion has occurred, the mode pins have
to be set back to the desired configuration mode.
2. Use of external components to offset the leakage. Current
mirrors can be used to introduce a current that off-sets the
leakage while the configuration is completing.
Virtex Devices -
Virtex devices are fully Hot Swap Capable. Virtex devices will not
have default pull-ups on the I/O pins during configuration so the
leakage current is not an issue.
Solution 3:
Using Xilinx PCI for Hot Swap:
The LogiCORE PCI Interface -
The Xilinx PCI32 and PCI64 Interfaces are Hot Swap Friendly
since they have the ability to add the Hot Swap Control and
Status register (HS_CSR) to the back end.
End of Record #5261 - Last Modified: 10/25/99 16:03 |
