Internals

NetFPGA internals

This page is dedicated for people doing very intrussive development related with NetFPGA card. It basically contains stuff that is needed to implement kernel-related code and is dedicated to OS developers willing to provide kernel drivers for NetFPGA hardware.

Information present on this page at the time of writing (2009.09.05) should be actual for releases newer than 1.2.5 version.

As an addition, libnetfpga API is mentioned each time particular functionality can be operated from the user-space. libnetfpga has been created with ease of NetFPGA operation in mind.

Computer booting

From the host PC point of view, NetFPGA appears on the PCI bus as a standard peripherial. It is identified with Device Identification and Device Vendor information. Exact numbers can be seen in `nf2kernel.h` file:

 /* Define PCI Vendor and device IDs for the NF2 card */
 #define PCI_VENDOR_ID_STANFORD          0xFEED
 #define PCI_DEVICE_ID_STANFORD_NF2      0x0001

Once it's been done, it's up to the developer to allocate needed resources. In terms of memory, card will operate on 2048-byte buffers, since it's the maximum value of the card's DMA transfer.

CPCI (Spartan) reprogramming

Default bitstream with which NetFPGA ships is broken . If you try to setup an interrupt handler, even if the data isn't present on any port and even without any cable plugged in, you'll be getting interrupts from DMA.

That's why CPCI reprogramming is mandatory .

PCI register values for NetFPGA card must be saved prior to touching CPCI. Reprogramming will change particular registers. After reprogramming, PCI registers must be restored back to the original values. Otherwise, card won't work properly.

Saving/receiving can be done either in the user-space (current code for GNU/Linux does that) or in the kernel-space (FreeBSD kernel driver does that).

CPCI reprogramming can easily be done with libnetfpga :

 int nf_cpci_write(struct netfpga *nf, const char *fname);

Where 'nf' is a handler returned by 'nf_start()', and 'fname' is a path to the bitstream file. Non-zero value is returned on error.

CNET (Virtex) reprogramming

Virtex programming is pretty straightforward.

With libnetfpga it can be done with;

 int nf_image_write(struct netfpga *nf, const char *fname)

Values of `nf' and 'fname' are respective to the 'nf_cpci_write' case.

Data receiving

Existance of data to parse is being done with 2 interrupts:

• "Data available"

At this stage it's up to the kernel code to involve a DMA transfer

• "Receiving finished"

Data transmission

• Minimum transfer size is 60 bytes.

Transfers smaller than this size have to be explicitly handled by the developer.

Summary

Hopefully this description will provide help for people trying to write low-level software for NetFPGA card.