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zsh - On-board serial HDLC/SDLC interface

#include <fcntl.h>

open(/dev/zshn, mode );

open(/dev/zsh, mode );

The zsh module is a loadable STREAMS driver that implements the sending and receiving of data packets as HDLC frames over synchronous serial lines. The module is not a standalone driver, but instead depends upon the zs module for the hardware support required by all on-board serial devices. When loaded this module acts as an extension to the zs driver, providing access to an HDLC interface through character-special devices.

The zshn devices provide what is known as a data path which supports the transfer of data via read(2) and write(2) system calls, as well as ioctl(2) calls. Data path opens are exclusive in order to protect against injection or diversion of data by another process.

The zsh device provides a separate control path for use by programs that need to configure or monitor a connection independent of any exclusive access restrictions imposed by data path opens. Up to three control paths may be active on a particular serial channel at any one time. Control path accesses are restricted to ioctl(2) calls only; no data transfer is possible.

When used in synchronous modes, the Z8530 SCC supports several options for clock sourcing and data encoding. Both the transmit and receive clock sources can be set to be the external Transmit Clock (TRxC), external Receive Clock (RTxC), the internal Baud Rate Generator (BRG), or the output of the SCC's Digital Phase-Lock Loop (DPLL).

The Baud Rate Generator is a programmable divisor that derives a clock frequency from the PCLK input signal to the SCC. A programmed baud rate is translated into a 16-bit time constant that is stored in the SCC. When using the BRG as a clock source the driver may answer a query of its current speed with a value different from the one specified. This is because baud rates translate into time constants in discrete steps, and reverse translation shows the change. If an exact baud rate is required that cannot be obtained with the BRG, an external clock source must be selected.

Use of the DPLL option requires the selection of NRZI data encoding and the setting of a non-zero value for the baud rate, because the DPLL uses the BRG as its reference clock source.

A local loopback mode is available, primarily for use by the syncloop(1M) utility for testing purposes, and should not be confused with SDLC loop mode, which is not supported on this interface. Also, an auto-echo feature may be selected that causes all incoming data to be routed to the transmit data line, allowing the port to act as the remote end of a digital loop. Neither of these options should be selected casually, or left in use when not needed.

The zsh driver keeps running totals of various hardware generated events for each channel. These include numbers of packets and characters sent and received, abort conditions detected by the receiver, receive CRC errors, transmit underruns, receive overruns, input errors and output errors, and message block allocation failures. Input errors are logged whenever an incoming message must be discarded, such as when an abort or CRC error is detected, a receive overrun occurs, or when no message block is available to store incoming data. Output errors are logged when the data must be discarded due to underruns, CTS drops during transmission, CTS timeouts, or excessive watchdog timeouts caused by a cable break.

The zsh driver supports several ioctl() commands, including: S_IOCGETMODE

S_IOCSETMODE S_IOCGETSTATS S_IOCCLRSTATS S_IOCGETSPEED S_IOCGETMCTL

The following structures are used with zsh ioctl() commands:

struct scc_mode {
 char sm_txclock; /* transmit clock sources */
 char sm_rxclock; /* receive clock sources */
 char sm_iflags; /* data and clock inversion flags (non-zsh) */
 uchar_t sm_config; /* boolean configuration options */
 int sm_baudrate; /* real baud rate */
 int sm_retval; /* reason codes for ioctl failures */
};
struct sl_stats {
 long ipack; /* input packets */
 long opack; /* output packets */
 long ichar; /* input bytes */
 long ochar; /* output bytes */
 long abort; /* abort received */
 long crc; /* CRC error */
 long cts; /* CTS timeouts */
 long dcd; /* Carrier drops */
 long overrun; /* receive overrun */
 long underrun; /* transmit underrun */
 long ierror; /* input error */
 long oerror; /* output error */
 long nobuffers; /* receive side memory allocation failure */
};

An open() will fail if a STREAMS message block cannot be allocated, or: ENXIO

EBUSY

An ioctl() will fail if: EINVAL

EINVAL /dev/zsh[0-1],/dev/zsh /usr/include/sys/ser_sync.h

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE ATTRIBUTE VALUE

Architecture x86

syncinit(1M), syncloop(1M), syncstat(1M), ioctl(2), open(2), read(2), write(2), attributes(5), zs(7D)

Refer to the Zilog Z8530 SCC Serial Communications Controller Technical Manual for details of the SCC's operation and capabilities.

zsh data open failed, no memory, rq=nnn zsh clone open failed, no memory, rq=nnn zsh_open: can't alloc message block zsh: clone device d must be attached before use! zshn: invalid operation for clone dev. zshn: not initialized, can't send message zshn: transmit hung