SMB(4)

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. In order 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 {
    	char cmd;
    	int count;
    	u_char slave;
    	union {
    		char byte;
    		short word;
    		char *byte_ptr;
    		short *word_ptr;
    		struct {
    			short sdata;
    			short *rdata;
    		} process;
    	} data;
    };

The slave field is always used, and provides the address of the SMBus slave device to talk to. 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 |
The QuickWrite command just issues the device address with write intent to the bus, without transferring any data.
SMB_QUICK_READ |
The QuickRead command just issues the device address with read intent to the bus, without transferring any data.
SMB_SENDB |
The SendByte command sends the byte provided in the cmd field to the device.
SMB_RECVB |
The ReceiveByte command reads a single byte from the device which will be returned in the cmd field.
SMB_WRITEB |
The WriteByte command first sends the byte from the cmd field to the device, followed by the byte given in data.byte.
SMB_WRITEW |
The WriteWord command first sends the byte from the cmd field to the device, followed by the word given in data.word. Note that the SMBus byte-order is little-endian by definition.
SMB_READB |
The ReadByte command first sends the byte from the cmd field to the device, and then reads one byte of data from the device. The returned data will be stored in the location pointed to by data.byte_ptr.
SMB_READW |
The ReadWord command first sends the byte from the cmd field to the device, and then reads one word of data from the device. The returned data will be stored in the location pointed to by data.word_ptr.
SMB_PCALL |
The ProcedureCall command first sends the byte from the cmd field to the device, followed by the word provided in data.process.sdata. It then reads one word of data from the device, and returns it in the location pointed to by data.process.rdata.
SMB_BWRITE |
The BlockWrite command first sends the byte from the cmd field to the device, followed by count bytes of data that are taken from the buffer pointed to by data.byte_ptr. 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 is available in the constant SMB_MAXBLOCKSIZE.
SMB_BREAD |
The BlockRead command first sends the byte from the cmd field to the device, and then reads count bytes of data that from the device. These data will be returned in the buffer pointed to by data.byte_ptr.

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.