Pin Constraints File (.pcf)

Note

This file is in a different usage than the Pin Constraints File in XML format (see details in Pin Constraints File (.xml))

The PCF file is the file which users should craft to assign their I/O constraints.

Built-in Commands

An example of a standard PCF file is shown as follows:

set_io a pad_fpga_io[0]
set_io b[0] pad_fpga_io[4]
set_io c[1] pad_fpga_io[6]

set_io <net> <pin>

Assign a net (defined as an input or output in users’ HDL design) to a specific pin of an FPGA device (typically a packaged chip).

Note

The net should be single-bit and match the port declaration of the top-module in users’ HDL design

Note

FPGA devices have different pin names, depending on their naming rules. Please contact your vendor for details.

Note

Built-in PCF commands cannot be overloaded.

Custom Commands

In addition to standard pin assignment commands, the PCF file supports custom commands defined in PCF Custom Command Configuration File (.xml). These commands provide a structured way for users to configure platform-specific hardware features through PCF.

Note

Custom PCF commands allow users to specify platform-specific configuration options (such as delay chains or peripheral modes) without dealing with low-level bitstream encodings. The detailed behavior, valid options, and encoding rules of each custom command are defined in PCF Custom Command Configuration File (.xml) and automatically interpreted by the PCF parser.

An example of PCF file using custom commands is shown as follows:

# Configure a delay chain on input pad pad_fpga_i[0]
# The detailed step and range are defined in the configuration file.
# The user only needs to specify the delay value.
# The PCF parser automatically encodes this into configuration bits.
set_delay_chain -pad pad_fpga_i[0] -delay 18446744073709551614

# Configure a watchdog peripheral on output pad pad_fpga_o[0]
# The user specifies the operating mode by name.
# The PCF parser automatically maps the mode to configuration bits.
set_watch_dog -pad pad_fpga_o[0] -mode NORMAL

<custom_command_name> <option> <value> ...

Note

Each option must match the definitions in PCF Custom Command Configuration File (.xml). The value provided must be valid according to the configuration file. The PCF parser will automatically validate and encode the values.