65 lines
3.1 KiB
Text
65 lines
3.1 KiB
Text
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fmc-chardev
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===========
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This is a simple generic driver, that allows user access by means of a
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character device (actually, one for each mezzanine it takes hold of).
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The char device is created as a misc device. Its name in /dev (as
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created by udev) is the same name as the underlying FMC device. Thus,
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the name can be a silly fmc-0000 look-alike if the device has no
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identifiers nor bus_id, a more specific fmc-0400 if the device has a
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bus-specific address but no associated name, or something like
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fdelay-0400 if the FMC core can rely on both a mezzanine name and a bus
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address.
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Currently the driver only supports read and write: you can lseek to the
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desired address and read or write a register.
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The driver assumes all registers are 32-bit in size, and only accepts a
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single read or write per system call. However, as a result of Unix read
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and write semantics, users can simply fread or fwrite bigger areas in
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order to dump or store bigger memory areas.
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There is currently no support for mmap, user-space interrupt management
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and DMA buffers. They may be added in later versions, if the need
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arises.
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The example below shows raw access to a SPEC card programmed with its
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golden FPGA file, that features an SDB structure at offset 256 - i.e.
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64 words. The mezzanine's EEPROM in this case is not programmed, so the
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default name is fmc-<bus><devfn>, and there are two cards in the system:
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spusa.root# insmod fmc-chardev.ko
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[ 1073.339332] spec 0000:02:00.0: Driver has no ID: matches all
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[ 1073.345051] spec 0000:02:00.0: Created misc device "fmc-0200"
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[ 1073.350821] spec 0000:04:00.0: Driver has no ID: matches all
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[ 1073.356525] spec 0000:04:00.0: Created misc device "fmc-0400"
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spusa.root# ls -l /dev/fmc*
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crw------- 1 root root 10, 58 Nov 20 19:23 /dev/fmc-0200
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crw------- 1 root root 10, 57 Nov 20 19:23 /dev/fmc-0400
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spusa.root# dd bs=4 skip=64 count=1 if=/dev/fmc-0200 2> /dev/null | od -t x1z
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0000000 2d 42 44 53 >-BDS<
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0000004
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The simple program tools/fmc-mem in this package can access an FMC char
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device and read or write a word or a whole area. Actually, the program
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is not specific to FMC at all, it just uses lseek, read and write.
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Its first argument is the device name, the second the offset, the third
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(if any) the value to write and the optional last argument that must
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begin with "+" is the number of bytes to read or write. In case of
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repeated reading data is written to stdout; repeated writes read from
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stdin and the value argument is ignored.
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The following examples show reading the SDB magic number and the first
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SDB record from a SPEC device programmed with its golden image:
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spusa.root# ./fmc-mem /dev/fmc-0200 100
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5344422d
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spusa.root# ./fmc-mem /dev/fmc-0200 100 +40 | od -Ax -t x1z
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000000 2d 42 44 53 00 01 02 00 00 00 00 00 00 00 00 00 >-BDS............<
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000010 00 00 00 00 ff 01 00 00 00 00 00 00 51 06 00 00 >............Q...<
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000020 c9 42 a5 e6 02 00 00 00 11 05 12 20 2d 34 42 57 >.B......... -4BW<
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000030 73 6f 72 43 72 61 62 73 49 53 47 2d 00 20 20 20 >sorCrabsISG-. <
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000040
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