89 lines
3.7 KiB
Text
89 lines
3.7 KiB
Text
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FMC (FPGA Mezzanine Card) is the standard we use for our I/O devices,
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in the context of White Rabbit and related hardware.
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In our I/O environments we need to write drivers for each mezzanine
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card, and such drivers must work regardless of the carrier being used.
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To achieve this, we abstract the FMC interface.
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We have a carrier for PCI-E called SPEC and one for VME called SVEC,
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but more are planned. Also, we support stand-alone devices (usually
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plugged on a SPEC card), controlled through Etherbone, developed by GSI.
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Code and documentation for the FMC bus was born as part of the spec-sw
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project, but now it lives in its own project. Other projects, i.e.
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software support for the various carriers, should include this as a
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submodule.
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The most up to date version of code and documentation is always
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available from the repository you can clone from:
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git://ohwr.org/fmc-projects/fmc-bus.git (read-only)
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git@ohwr.org:fmc-projects/fmc-bus.git (read-write for developers)
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Selected versions of the documentation, as well as complete tar
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archives for selected revisions are placed to the Files section of the
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project: `http://www.ohwr.org/projects/fmc-bus/files'
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What is FMC
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***********
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FMC, as said, stands for "FPGA Mezzanine Card". It is a standard
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developed by the VME consortium called VITA (VMEbus International Trade
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Association and ratified by ANSI, the American National Standard
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Institute. The official documentation is called "ANSI-VITA 57.1".
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The FMC card is an almost square PCB, around 70x75 millimeters, that is
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called mezzanine in this document. It usually lives plugged into
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another PCB for power supply and control; such bigger circuit board is
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called carrier from now on, and a single carrier may host more than one
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mezzanine.
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In the typical application the mezzanine is mostly analog while the
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carrier is mostly digital, and hosts an FPGA that must be configured to
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match the specific mezzanine and the desired application. Thus, you may
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need to load different FPGA images to drive different instances of the
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same mezzanine.
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FMC, as such, is not a bus in the usual meaning of the term, because
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most carriers have only one connector, and carriers with several
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connectors have completely separate electrical connections to them.
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This package, however, implements a bus as a software abstraction.
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What is SDB
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***********
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SDB (Self Describing Bus) is a set of data structures that we use for
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enumerating the internal structure of an FPGA image. We also use it as
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a filesystem inside the FMC EEPROM.
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SDB is not mandatory for use of this FMC kernel bus, but if you have SDB
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this package can make good use of it. SDB itself is developed in the
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fpga-config-space OHWR project. The link to the repository is
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`git://ohwr.org/hdl-core-lib/fpga-config-space.git' and what is used in
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this project lives in the sdbfs subdirectory in there.
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SDB support for FMC is described in *note FMC Identification:: and
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*note SDB Support::
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SDB Support
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***********
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The fmc.ko bus driver exports a few functions to help drivers taking
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advantage of the SDB information that may be present in your own FPGA
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memory image.
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The module exports the following functions, in the special header
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<linux/fmc-sdb.h>. The linux/ prefix in the name is there because we
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plan to submit it upstream in the future, and don't want to force
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changes on our drivers if that happens.
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int fmc_scan_sdb_tree(struct fmc_device *fmc, unsigned long address);
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void fmc_show_sdb_tree(struct fmc_device *fmc);
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signed long fmc_find_sdb_device(struct sdb_array *tree, uint64_t vendor,
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uint32_t device, unsigned long *sz);
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int fmc_free_sdb_tree(struct fmc_device *fmc);
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