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`.