Ubuntu Manpage: smb — SMB generic I/O device driver

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NAME

       smb — SMB generic I/O device driver

SYNOPSIS

       device smb

DESCRIPTION

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.

ERRORS

       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.

HISTORY

       The smb manual page first appeared in FreeBSD 3.0.

AUTHORS