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.

SEE ALSO

     ioctl(2), smbus(4)

HISTORY

     The smb manual page first appeared in FreeBSD 3.0.

AUTHORS

     This manual page was written by Nicolas Souchu and extended by
     Michael Gmelin <freebsd@grem.de>.