smb
—
SMB generic I/O device driver
The smb character device driver provides generic I/O to any
smbus(4)
instance. To control SMB devices, use /dev/smb? with
the ioctls described below. Any of these ioctl commands takes a pointer to
struct smbcmd as its argument.
#include <sys/types.h>
struct smbcmd {
u_char cmd;
u_char reserved;
u_short op;
union {
char byte;
char buf[2];
short word;
} wdata;
union {
char byte;
char buf[2];
short word;
} rdata;
int slave;
char *wbuf; /* use wdata if NULL */
int wcount;
char *rbuf; /* use rdata if NULL */
int rcount;
};
The slave field is always used, and provides
the address of the SMBus slave device. The slave address is specified in the
seven most significant bits (i.e., “left-justified”). The
least significant bit of the slave address must be zero.
Ioctl |
Description
|
SMB_QUICK_WRITE |
QuickWrite does not transfer any data. It just issues
the device address with write intent to the bus. |
SMB_QUICK_READ |
QuickRead does not transfer any data. It just issues
the device address with read intent to the bus. |
SMB_SENDB |
SendByte sends the byte provided in
cmd to the device. |
SMB_RECVB |
ReceiveByte reads a single byte from the device which
is returned in cmd. |
SMB_WRITEB |
WriteByte first sends the byte from
cmd to the device, followed by the byte given in
wdata.byte. |
SMB_WRITEW |
WriteWord first sends the byte from
cmd to the device, followed by the word given in
wdata.word. Note that the SMBus byte-order is
little-endian by definition. |
SMB_READB |
ReadByte first sends the byte from
cmd to the device, then reads one byte of data from
the device. Returned data is stored in
rdata.byte. |
SMB_READW |
ReadWord first sends the byte from
cmd to the device, then reads one word of data from
the device. Returned data is stored in
rdata.word. |
SMB_PCALL |
ProcedureCall first sends the byte from
cmd to the device, followed by the word provided in
wdata.word. It then reads one word of data from the
device and returns it in rdata.word. |
SMB_BWRITE |
BlockWrite first sends the byte from
cmd to the device, then the byte from
wcount followed by wcount
bytes of data that are taken from the buffer pointed to by
wbuf. The SMBus specification mandates that no more
than 32 bytes of data can be transferred in a single block read or write
command. This value can be read from the constant
SMB_MAXBLOCKSIZE . |
SMB_BREAD |
BlockRead first sends the byte from
cmd to the device, then reads a count of data bytes
that the device is going to provide and then reads that many bytes. The
count is returned in rcount. The data is returned in
the buffer pointed to by rbuf. |
The
read(2)
and
write(2)
system calls are not implemented by this driver.
The ioctl(2)
commands can cause the following driver-specific errors:
- [
ENXIO
]
- Device did not respond to selection.
- [
EBUSY
]
- Device still in use.
- [
ENODEV
]
- Operation not supported by device (not supposed to happen).
- [
EINVAL
]
- General argument error.
- [
EWOULDBLOCK
]
- SMBus transaction timed out.
The smb
manual page first appeared in
FreeBSD 3.0.
This manual page was written by Nicolas Souchu and
extended by
Michael Gmelin ⟨freebsd@grem.de⟩.