ecpp - IEEE 1284 compliant parallel port driver


#include <sys/types.h>

#include <sys/ecppio.h>



The ecpp driver provides a bi-directional interface to IEEE 1284
compliant devices as well as a forward single-directional interface to
Centronics devices. In addition to the Centronics protocol, the ecpp
driver supports the IEEE 1284 Compatibility, Nibble, and ECP protocols.
ECPP_COMPAT_MODE and ECPP_CENTRONICS modes of operation have logically
identical handshaking protocols, however devices that support
ECPP_COMPAT_MODE are IEEE 1284 compliant devices. IEEE 1284 compliant
devices support at least ECPP_COMPAT_MODE and ECPP_NIBBLE_MODE.
Centronics devices support only ECPP_CENTRONICS mode.

By default, ECPP_COMPAT_MODE devices have a strobe handshaking pulse
width of 500ns. For this mode, forward data transfers are conducted by
DMA. By default, the strobe pulse width for ECPP_CENTRONICS devices is
two microseconds. Forward transfers for these devices are managed through
PIO. The default characteristics for both ECPP_COMPAT_MODE and
ECPP_CENTRONICS devices may be changed through tunable variables defined
in ecpp.conf.

The ecpp driver is an exclusive-use device, meaning that if the device is
already open, subsequent opens fail with EBUSY.

Default Operation

Each time the ecpp device is opened, the device is marked as EBUSY and
the configuration variables are set to their default values. The
write_timeout period is set to 90 seconds.

The driver sets the mode variable according to the following algorithm:
The driver initially attempts to negotiate the link into ECPP_ECP_MODE
during open(2). If it fails, the driver tries to negotiate into
ECPP_NIBBLE_MODE mode. If that fails, the driver operates in
ECPP_CENTRONICS mode. Upon successfully opening the device, IEEE 1284
compliant devices will be left idle in either reverse idle phase of
ECPP_ECP_MODE or in ECPP_NIBBLE_MODE. Subsequent calls to write(2)
invokes the driver to move the link into either ECPP_COMPAT_MODE or the
forward phase of ECPP_ECP_MODE. After the transfer completes, the link
returns to idle state.

The application may attempt to negotiate the device into a specific mode
or set the write_timeout values through the ECPPIOC_SETPARMS ioctl(2)
call. For mode negotiation to be successful, both the host workstation
and the peripheral must support the requested mode.


Characteristics of the ecpp driver may be tuned by the variables
described in /kernel/drv/ecpp.conf. These variables are read by the
kernel during system startup. To tune the variables, edit the ecpp.conf
file and invoke update_drv(8) to have the kernel read the file again.

Some Centronics peripherals and certain IEEE 1284 compatible peripherals
will not operate with the parallel port operating in a fast handshaking
mode. If printing problems occur, set "fast-centronics" and
"fast-1284-compatible" to "false." See /kernel/drv/ecpp.conf for more

Read/Write Operation
The ecpp driver is a full duplex STREAMS device driver. While an
application is writing to an IEEE 1284 compliant device, another thread
may read from it.

Write Operation

A write(2) operation returns the number of bytes successfully written to
the stream head. If a failure occurs while a Centronics device is
transferring data, the content of the status bits will be captured at the
time of the error and can be retrieved by the application program using
the BPPIOC_GETERR ioctl(2) call. The captured status information is
overwritten each time an attempted transfer or a BPPIOC_TESTIO ioctl(2)

Read Operation

If a failure or error condition occurs during a read(2), the number of
bytes successfully read is returned (short read). When attempting to read
a port that has no data currently available, read(2) returns 0 if
O_NDELAY is set. If O_NONBLOCK is set, read(2) returns -1 and sets errno
to EAGAIN. If O_NDELAY and O_NONBLOCK are clear, read(2) blocks until
data become available.


The ioctl(2) calls described below are supported. Note that when ecpp is
transferring data, the driver waits until the data has been sent to the
device before processing the ioctl(2) call.

The ecpp driver supports prnio(4I) interfaces.

Note -

The PRNIOC_RESET command toggles the nInit signal for 2 ms, followed by
default negotiation.

The following ioctl(2) calls are supported for backward compatibility and
are not recommended for new applications:

Get current transfer parameters. The argument is a
pointer to a struct ecpp_transfer_parms. See below
for a description of the elements of this structure.
If no parameters have been configured since the
device was opened, the structure will be set to its
default configuration. See Default Operation above
for more information.

Set transfer parameters. The argument is a pointer to
a struct ecpp_transfer_parms. If a parameter is out
of range, EINVAL is returned. If the peripheral or
host device cannot support the requested mode,
EPROTONOSUPPORT is returned. See below for a
description of ecpp_transfer_parms and its valid

The Transfer Parameters Structure is defined in

struct ecpp_transfer_parms {
int write_timeout;
int mode;

The write_timeout field is set to the value of ecpp-
transfer-timeout specified in the ecpp.conf. The
write_timeout field specifies how long the driver
will wait for the peripheral to respond to a transfer
request. The value must be greater than 0 and less
than ECPP_MAX_TIMEOUT. All other values are out of

The mode field reflects the IEEE 1284 mode to which
the parallel port is currently configured. The mode
may be set to one of the following values only:
ECPP_ECP_MODE. All other values are invalid. If the
requested mode is not supported, ECPPIOC_SETPARMS
will return EPROTONOSUPPORT and the mode will be set
to ECPP_CENTRONICS mode. Afterwards, the application
may change the mode back to the original mode with

This ioctl gets the IEEE 1284 device ID from the
peripheral in specified mode. Currently, the device
ID can be retrieved only in Nibble mode. A pointer to
the structure defined in <sys/ecppsys.h> must be
passed as an argument.

The 1284 device ID structure:

struct ecpp_device_id {
int mode; /* mode to use for reading device id */
int len; /* length of buffer */
int rlen; /* actual length of device id string */
char *addr; /* buffer address */

The mode is the IEEE 1284 mode into which the port
will be negotiated to retrieve device ID information.
If the peripheral or host do not support the mode,
EPROTONOSUPPORT is returned. Applications should set
mode to ECPP_NIBBLE_MODE. len is the length of the
buffer pointed to by addr. rlen is the actual length
of the device ID string returned from the peripheral.
If the returned rlen is greater than len, the
application can call ECPPIOC_GETDEVID again with a
buffer length equal or greater than rlen. Note that
the two length bytes of the IEEE 1284 device ID are
not taken into account and are not returned in the
user buffer.

After ECPPIOC_GETDEVID successfully completes, the
driver returns the link to ECPP_COMPAT_MODE. The
application is responsible for determining the
previous mode the link was operating in and returning
the link to that mode.

Tests the forward transfer readiness of a peripheral
operating in Centronics or Compatibility mode.

TESTIO determines if the peripheral is ready to
receive data by checking the open flags and the
Centronics status signals. If the current mode of the
device is ECPP_NIBBLE_MODE, the driver negotiates the
link into ECPP_COMPAT_MODE, check the status signals
and then return the link to ECPP_NIBBLE_MODE mode. If
the current mode is ECPP_CENTRONICS or
ECPP_COMPAT_MODE, TESTIO examines the Centronics
status signals in the current mode. To receive data,
the device must have the nErr and Select signals
asserted and must not have the PE and Busy signals
asserted. If ecpp is transferring data, TESTIO waits
until the previous data sent to the driver is
delivered before executing TESTIO. However if an
error condition occurs while a TESTIO is waiting,
TESTIO returns immediately. If TESTIO determines that
the conditions are ok, 0 is returned. Otherwise, -1
is returned, errno is set to EIO and the state of the
status pins is captured. The captured status can be
retrieved using the BPPIOC_GETERR ioctl(2) call. The
timeout_occurred and bus_error fields will never be
set by this ioctl(2).

Get last error status. The argument is a pointer to a
struct bpp_error_status defined in <sys/bpp_io.h>
header file. The error status structure is:

struct bpp_error_status {
char timeout_occurred; /* 1=timeout */
char bus_error; /* not used */
uchar_t pin_status; /* status of pins which
/* could cause error */

The pin_status field indicates possible error
conditions. The valid bits for pin_status are:
A set bit indicates that the associated pin is

This structure indicates the status of all the
appropriate status bits at the time of the most
recent error condition during a write(2) call, or the
status of the bits at the most recent BPPIOC_TESTIO

pin_status indicates possible error conditions under
modes, the state of the status pins will indicate the
state of the device. For instance, many Centronics
printers lower the nErr signal when a paper jam
occurs. The behavior of the status pins depends on
the device. Additional status information may be
retrieved through the backchannel.

The timeout_occurred value is set when a timeout
occurs during write(2). bus_error is not used in this

The following ioctls are used to directly read and write the parallel
port status and control signals. If the current mode of the device is
ECPP_ECP_MODE or ECPP_NIBBLE_MODE, the driver negotiates the link into
ECPP_COMPAT_MODE, gets or sets the registers and then returns the link to
ECPP_NIBBLE_MODE. If the current mode is ECPP_CENTRONICS or
ECPP_COMPAT_MODE, these ioctls will get/set the register values in the
current mode.

Read register values. The argument is a pointer to a
struct ecpp_regs. See below for a description of this

Set ecpp register values. The argument is a pointer to
a struct ecpp_regs. See below for a description of
this structure. If a parameter is out of range, EINVAL
is returned.

The Port Register Structure is defined in

struct ecpp_regs {
uchar dsr; /* status reg */
u_char dcr; /* control reg */

The status register is read-only. The ECPPIOC_SETREGS
ioctl has no affect on this register. Valid bit values
ECPP_nBUSY. All other bits are reserved and always
return 1.

The control register is read/write. Valid bit values
for dcr are: ECPP_STB, ECPP_AFX, ECPP_nINIT,
ECPP_SLCTIN. All other bits are reserved. Reading
reserved bits always return 1. An attempt to write 0s
into these bits results in EINVAL.


x86 only. (Backwards compatibility with former lp(4D)

1284 compliant parallel port device special files
appears in both namespaces.



Device driver (SPARC)


Device driver (x86)


Driver configuration file


The device is opened for write-only access and a read is
attempted, or the device is opened for read-only access and a
write is attempted.

The device has been opened and another open is attempted. An
attempt has been made to unload the driver while one of the
units is open.

A ECPPIOC_SETPARMS ioctl() is attempted with an out-of-range
value in the ecpp_transfer_parms structure. A ECPPIOC_SETREGS
ioctl() is attempted with an invalid value in the ecpp_regs
structure. An ioctl() is attempted with an invalid value in the
command argument.An invalid command argument is received during
modload(8) or modunload(8).

The driver encountered a bus error when attempting an access. A
read or write did not complete properly, due to a peripheral
error or a transfer timeout.

The driver has received an open request for a unit for which
the attach failed. The driver has received a write request for
a unit which has an active peripheral error.


See attributes(7) for descriptions of the following attributes:

|Architecture | PCI-based systems |
| | ISA-based systems (x86) |
|Interface stability | Evolving |


ioctl(2), open(2), read(2), write(2), usbprn(4D), prnio(4I),
streamio(4I), attributes(7), modload(8), modunload(8), update_drv(8)

IEEE Std 1284-1994


Parallel port controller not supported

Driver does not support parallel port controller on the given host.
Attach failed.

May 17, 2020 ECPP(4D)