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fpga - interface to on-board FPGA


bind -a #F /dev



Fpga allows configuration of an on-board FPGA (eg, the Altera Flex6000 on the Bright Star Engineering ip-Engine), control of its clocks and environment, and raw access to any devices presented in the FPGA address space. On booting, the FPGA subsystem is normally left powered down and the system's external clocks are not directed to the processor's output pins, to conserve power if the subsystem is unused.

The control file fpgactl accepts the following requests:

bclk n
Set BCLK output to n MHz, where n must be a divisor of the system clock frequency (eg, of 48 if the system is running at 48 MHz).
Power up the FPGA subsystem (that is automatically done when fpgaprog is accessed).
power off
Power down the FPGA subsystem.
Reset the FPGA, forcing it into configuration mode (automatically done when fpgaprog is accessed).
vclk n m v r
Program the clock synthesiser with the given parameters, and enable its output as VCLK.
vclk off
Disable output from the clock synthesiser.

The files fpgamemb and fpgamemw give 8-bit and 16-bit access respectively to the address space interpreted by the FPGA. The file offset is the address read or written within that space; offset and count must both be even for fpgamemw. The interpretation of the data, including the data format and whether byte or word access is required, is completely determined by the program configured into the FPGA.

The write-only file fpgaprog configures the device. A single write provides an FPGA configuration in raw binary format. The FPGA subsystem is given power, the processor's clocks are made visible externally, and the device is configured with the data written. The write returns an error if configuration fails.

The read-only file fpgastatus contains a single line of text giving the state of the two status bits in the FPGA interface. The word config appears if CONFIG_DONE is set, and !config otherwise; the word status appears if nSTATUS is set, and !status otherwise.





FPGA(3 ) Rev:  Thu Feb 15 14:43:36 GMT 2007