EP4CE30F29C7N Datasheet, PDF (255/488 Pages) Altera Corporation – Cyclone IV Device Handbook, Volume 1

Chapter 9: SEU Mitigation in Cyclone IV Devices
9–9
Recovering from CRC Errors
Table 9–7 lists the input and output ports that you must include in the atom.
Table 9–7. CRC Block Input and Output Ports
Port
Input/Output
Definition
<crcblock_name>
Input
Unique identifier for the CRC block, and represents any identifier name that is legal
for the given description language (for example, Verilog HDL, VHDL, and AHDL).
This field is required.
.clk(<clock source>
Input
This signal designates the clock input of this cell. All operations of this cell are
with respect to the rising edge of the clock. Whether it is the loading of the data
into the cell or data out of the cell, it always occurs on the rising edge. This port is
required.
.shiftnld (<shiftnld
source>)
Input
This signal is an input into the error detection block. If shiftnld=1, the data is
shifted from the internal shift register to the regout at each rising edge of clk. If
shiftnld=0, the shift register parallel loads either the pre-calculated CRC value
or the update register contents, depending on the ldsrc port input. To do this,
the shiftnld must be driven low for at least two clock cycles. This port is
required.
.ldsrc (<ldsrc
source>)
Input
This signal is an input into the error detection block. If ldsrc=0, the
pre-computed CRC register is selected for loading into the 32-bit shift register at
the rising edge of clk when shiftnld=0. If ldsrc=1, the signature register
(result of the CRC calculation) is selected for loading into the shift register at the
rising edge of clk when shiftnld=0. This port is ignored when
shiftnld=1. This port is required.
.crcerror (<crcerror
indicator
output>)
.regout (<registered
output>)
Output
Output
This signal is the output of the cell that is synchronized to the internal oscillator of
the device (80-MHz internal oscillator) and not to the clk port. It asserts high if
the error block detects that a SRAM bit has flipped and the internal CRC
computation has shown a difference with respect to the pre-computed value. You
must connect this signal either to an output pin or a bidirectional pin. If it is
connected to an output pin, you can only monitor the CRC_ERROR pin (the core
cannot access this output). If the CRC_ERROR signal is used by core logic to
read error detection logic, you must connect this signal to a BIDIR pin. The
signal is fed to the core indirectly by feeding a BIDIR pin that has its output
enable port connected to V_CC (see Figure 9–3 on page 9–8).
This signal is the output of the error detection shift register synchronized to the
clk port to be read by core logic. It shifts one bit at each cycle, so you should
clock the clk signal 31 cycles to read out the 32 bits of the shift register.
Recovering from CRC Errors
The system that the Altera FPGA resides in must control device reconfiguration. After
detecting an error on the CRC_ERROR pin, strobing the nCONFIG low directs the system
to perform the reconfiguration at a time when it is safe for the system to reconfigure
the FPGA.
When the data bit is rewritten with the correct value by reconfiguring the device, the
device functions correctly.
While soft errors are uncommon in Altera devices, certain high-reliability applications
might require a design to account for these errors.
May 2013 Altera Corporation
Cyclone IV Device Handbook,
Volume 1