Bus Commands¶

The 1-Wire bus defines different layers of access to the devices on the bus. The own functions provide access to the network and transport layers. The network layer designates the next command as being either for all devices on the bus, or for a specific device. The network layer also specifies the speed used by the link layer.

struct ow_cmd encapsulates network access, speed, and timing information. It specifies the commands to send and whether or not to read data. Its members are:

flags

Flags controlling the interpretation of the structure. These flags are defined in <dev/ow/ow.h>:

OW_FLAG_OVERDRIVE

Send xpt_cmd bytes and read xpt_read bytes at overdrive speed.

OW_FLAG_READ_BIT

Interpret xpt_read_len to be in bits to be read after xpt_cmd rather than bytes.

rom_cmd

ROM command bytes to send.

rom_len

Number of ROM command bytes to send.

rom_read_len

Number of bytes to read after sending the ROM command.

rom_read

Buffer for bytes read after the ROM command.

xpt_cmd

Transport command to send.

xpt_len

Length of the transport command bytes to send. Specify 0 for no transport command.

xpt_read_len

Number of bytes to read after xpt_cmd bytes are sent. If the OW_FLAG_READ_BIT bit is set in flags, then it is the number of bits to read. Bits read are packed into bytes.

xpt_read

Buffer for data read.

own_command_wait() acquires the 1-Wire bus, waiting if necessary, sends the command, and then releases the bus. own_send_command() sends the command without bus reservation. pdev is the client device (the presentation layer device) sending the command. The cmd argument describes the transaction to send to the 1-Wire bus.

own_self_command() fills in cmd with a MATCH_ROM ROM command, the ROM address of pdev and the xpt_cmd as a convenient way to create directed commands.

Bus Reservation¶

The 1-Wire system includes an advisory lock for the bus that presentation layer devices can use to coordinate access. Locking is purely advisory at this time.

own_acquire_bus() reserves the bus. It waits indefinitely if the how argument is OWN_WAIT and returns the error EWOULDBLOCK if passed OWN_DONTWAIT when the bus is owned by another client.

own_release_bus() releases the bus.

Data Integrity¶

own_crc() computes the 1-Wire standard CRC function over the data passed in buffer and len and returns the result.

Notes¶

The 1-Wire standard (Maxim AN937) defines layers that are akin to ISO networking layers. The lowest relevant layer, the link layer, defines the polling windows and the timing of the signaling of different modes. The network layer is built on top of the link layer and is used to address devices in a unicast or multicast manner. The transport layer defines commands and responses from the devices. The presentation layer is composed of the device specific commands and actions used to control the specific 1-Wire devices on bus.

These interfaces are implemented by the ow(4) device. Presentation layer devices (children of the newbus ow(4) device) should only call the functions described here. The functionality provided by the owc(4) device (specifically the owll(9) interface) should only be called by the ow(4) driver.