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Diffstat (limited to 'kernel/Documentation/fmc/fmc-chardev.txt')
| -rw-r--r-- | kernel/Documentation/fmc/fmc-chardev.txt | 64 |
1 files changed, 64 insertions, 0 deletions
diff --git a/kernel/Documentation/fmc/fmc-chardev.txt b/kernel/Documentation/fmc/fmc-chardev.txt new file mode 100644 index 000000000..d9ccb278e --- /dev/null +++ b/kernel/Documentation/fmc/fmc-chardev.txt @@ -0,0 +1,64 @@ +fmc-chardev +=========== + +This is a simple generic driver, that allows user access by means of a +character device (actually, one for each mezzanine it takes hold of). + +The char device is created as a misc device. Its name in /dev (as +created by udev) is the same name as the underlying FMC device. Thus, +the name can be a silly fmc-0000 look-alike if the device has no +identifiers nor bus_id, a more specific fmc-0400 if the device has a +bus-specific address but no associated name, or something like +fdelay-0400 if the FMC core can rely on both a mezzanine name and a bus +address. + +Currently the driver only supports read and write: you can lseek to the +desired address and read or write a register. + +The driver assumes all registers are 32-bit in size, and only accepts a +single read or write per system call. However, as a result of Unix read +and write semantics, users can simply fread or fwrite bigger areas in +order to dump or store bigger memory areas. + +There is currently no support for mmap, user-space interrupt management +and DMA buffers. They may be added in later versions, if the need +arises. + +The example below shows raw access to a SPEC card programmed with its +golden FPGA file, that features an SDB structure at offset 256 - i.e. +64 words. The mezzanine's EEPROM in this case is not programmed, so the +default name is fmc-<bus><devfn>, and there are two cards in the system: + + spusa.root# insmod fmc-chardev.ko + [ 1073.339332] spec 0000:02:00.0: Driver has no ID: matches all + [ 1073.345051] spec 0000:02:00.0: Created misc device "fmc-0200" + [ 1073.350821] spec 0000:04:00.0: Driver has no ID: matches all + [ 1073.356525] spec 0000:04:00.0: Created misc device "fmc-0400" + spusa.root# ls -l /dev/fmc* + crw------- 1 root root 10, 58 Nov 20 19:23 /dev/fmc-0200 + crw------- 1 root root 10, 57 Nov 20 19:23 /dev/fmc-0400 + spusa.root# dd bs=4 skip=64 count=1 if=/dev/fmc-0200 2> /dev/null | od -t x1z + 0000000 2d 42 44 53 >-BDS< + 0000004 + +The simple program tools/fmc-mem in this package can access an FMC char +device and read or write a word or a whole area. Actually, the program +is not specific to FMC at all, it just uses lseek, read and write. + +Its first argument is the device name, the second the offset, the third +(if any) the value to write and the optional last argument that must +begin with "+" is the number of bytes to read or write. In case of +repeated reading data is written to stdout; repeated writes read from +stdin and the value argument is ignored. + +The following examples show reading the SDB magic number and the first +SDB record from a SPEC device programmed with its golden image: + + spusa.root# ./fmc-mem /dev/fmc-0200 100 + 5344422d + spusa.root# ./fmc-mem /dev/fmc-0200 100 +40 | od -Ax -t x1z + 000000 2d 42 44 53 00 01 02 00 00 00 00 00 00 00 00 00 >-BDS............< + 000010 00 00 00 00 ff 01 00 00 00 00 00 00 51 06 00 00 >............Q...< + 000020 c9 42 a5 e6 02 00 00 00 11 05 12 20 2d 34 42 57 >.B......... -4BW< + 000030 73 6f 72 43 72 61 62 73 49 53 47 2d 00 20 20 20 >sorCrabsISG-. < + 000040 |