The special file /_d_e_v/_p_l_p refers to the parallel printer interface on the
Indigo, Indy, Indigo2, Challenge/Onyx, O2, OCTANE, Origin200 and Onyx2
products. Special file /_d_e_v/_p_l_p_b_i is also available on the Indigo, Indy
and Indigo2 platforms and is used to access the parallel printer
interface in bidirectional access mode.
The plp device supports output to a Centronics-compatible printer
connected to the builtin parallel printer port. Normally, /_d_e_v/_p_l_p is
directly accessed only by a print spooling mechanism such as the llllpppp((((1111))))
subsystem. Multiple processes may open the device, but these processes
must synchronize writes to prevent intermingled data. Processes may open
the device read-only to obtain printer status. The special file
/_d_e_v/_p_l_p_b_i may be open for reading and writing by one process at a time.
A printer reset is automatically issued only once at system startup.
Different platforms support different operation modes and features as
described below.
The plp devices on the O2 are IEEE 1284-II compliant and supports all
three IEEE 1284-II interfaces: Compatibility(Centronics), bidirectional
Enhanced Parallel Port(EPP), and bidirectional Extended Capabilities
Port(ECP). Bidirectional Centronics mode is not supported. Compatibility
(Centronics) mode is actually available as two different types: PIO or
FIFO mode. FIFO Compatibility mode is a faster Centronics mode which uses
DMA access. PIO Compatibility mode uses standard PIO access (no DMA). PIO
Compatibility mode has been found to be more compatible with some types
of printers and should be used only if problems occur in FIFO
Compatibility mode. The O2 plp driver also has the capability to perform
auto-negotiation with printers (peripherals) to set up the proper
protocol. This auto-negotiation mode, or any other supported mode, can be
specified through ////vvvvaaaarrrr////ssssyyyyssssggggeeeennnn////mmmmaaaasssstttteeeerrrr....dddd////eeeeccccppppllllpppp to override the default mode
(Compatibility FIFO mode).
The plp devices on the OCTANE, Origin200, and Onyx2 are IEEE 1284-II
compliant devices. However only Compatibility(Centronics) and Extended
Capabilities Port(ECP) output mode are supported. Bidirectional
Centronics, bidirectional ECP, EPP and auto-negotiation mode are not
supported. As with the O2 platform, Compatibility mode is available as
either FIFO or PIO Compatibility mode. The default operation mode