Each time the bpp device is opened, the default configuration is BPP_ACK_BUSY_HS for read handshake, BPP_ACK_HS for write handshake, 1 microsecond for all setup times and strobe widths, and 60 seconds for both timeouts. This configuration (in the write mode) drives many common personal computer parallel printers with Centronics-type interfaces. The application should use the BPPIOC_SETPARMS ioctl request to configure the bpp for the particular device which is attached, if necessary.

If a failure or error condition occurs during a write(2), the number of bytes successfully written is returned (short write). Note that errno will not be set. The contents of certain status bits will be captured at the time of the error, and can be retrieved by the application program, using the BPPIOC_GETERR ioctl request. Subsequent write(2) calls may fail with the system error ENXIO if the error condition is not rectified. The captured status information will be overwritten each time an attempted transfer or a BPPIOC_TESTIO ioctl request occurs.

If a failure or error condition occurs during a read(2), the number of bytes successfully read is returned (short read). Note that errno will not be set. The contents of certain status bits will be captured at the time of the error, and can be retrieved by the application, using the BPPIOC_GETERR ioctl request. Subsequent read(2) calls may fail with ENXIO if the error condition is not rectified. The captured register information will be overwritten each time an attempted transfer or a BPPIOC_TESTIO ioctl request.

If the read_handshake element of the bpp_transfer_parms structure (see below) is set to BPP_CLEAR_MEM or BPP_SET_MEM, zeroes or ones, respectively, are written into the user buffer.

When the driver is opened for reading and writing, it is assumed that scanning will take place, as scanners are the only devices supported by this mode. Most scanners require that the SLCT_IN or AFX pin be set to tell the scanner the direction of the transfer. The AFX line is set when the read_handshake element of the bpp_transfer_parms structure is set to BPP_HSCAN_HS, otherwise the SLCT_IN pin is set. Normally, scanning starts by writing a command to the scanner, at which time the pin is set. When the scan data is read back, the pin is reset.

This structure is defined in <sys/bpp_io.h>.

struct bpp_transfer_parms { enum handshake_t read_handshake; /* parallel port read handshake mode */ int read_setup_time; /* DSS register - in nanoseconds */ int read_strobe_width; /* DSW register - in nanoseconds */ int read_timeout; /* * wait this many seconds * before aborting a transfer */ enum handshake_t write_handshake; /* parallel port write handshake mode */ int write_setup_time; /* DSS register - in nanoseconds */ int write_strobe_width; /* DSW register - in nanoseconds */ int write_timeout; /* * wait this many seconds * before aborting a transfer */ }; /* Values for read_handshake and write_handshake fields */ enum handshake_t { BPP_NO_HS, /* no handshake pins */ BPP_ACK_HS, /* handshake controlled by ACK line */ BPP_BUSY_HS, /* handshake controlled by BSY line */ BPP_ACK_BUSY_HS, /* * handshake controlled by ACK and BSY lines * read_handshake only! */ BPP_XSCAN_HS, /* xerox scanner mode, * read_handshake only! */ BPP_HSCAN_HS, /* * HP scanjet scanner mode * read_handshake only! */ BPP_CLEAR_MEM, /* write 0's to memory, * read_handshake only! */ BPP_SET_MEM, /* write 1's to memory, * read_handshake only! */ /* The following handshakes are RESERVED. Do not use. */ BPP_VPRINT_HS, /* valid only in read/write mode */ BPP_VPLOT_HS /* valid only in read/write mode */ };

The read_setup_time field controls the time between dstrb falling edge to bsy rising edge if the read_handshake field is set to BPP_NO_HS or BPP_ACK_HS. It controls the time between dstrb falling edge to ack rising edge if the read_handshake field is set to BPP_ACK_HS or BPP_ACK_BUSY_HS. It controls the time between ack falling edge to dstrb rising edge if the read_handshake field is set to BPP_XSCAN_HS.

The read_strobe_width field controls the time between ack rising edge and ack falling edge if the read_handshake field is set to BPP_NO_HS or BPP_ACK_BUSY_HS. It controls the time between dstrb rising edge to dstrb falling edge if the read_handshake field is set to BPP_XSCAN_HS.

The values allowed for the write_handshake field are duplicates of the definitions for the read_handshake field. Note that some of these handshake definitions are only valid in one mode or the other.

The write_setup_time field controls the time between data valid to dstrb rising edge for all values of the write_handshake field.

The write_strobe_width field controls the time between dstrb rising edge and dstrb falling edge if the write_handshake field is not set to BPP_VPRINT_HS or BPP_VPLOT_HS. It controls the minimum time between dstrb rising edge to dstrb falling edge if the write_handshake field is set to BPP_VPRINT_HS or BPP_VPLOT_HS.

This structure is defined in <sys/bpp_io.h>.

struct bpp_pins { uchar_t output_reg_pins; /* pins in P_OR register */ uchar_t input_reg_pins; /* pins in P_IR register */ }; /* Values for output_reg_pins field */ #define BPP_SLCTIN_PIN 0x01 /* Select in pin */ #define BPP_AFX_PIN 0x02 /* Auto feed pin */ #define BPP_INIT_PIN 0x04 /* Initialize pin */ #define BPP_V1_PIN 0x08 /* reserved pin 1 */ #define BPP_V2_PI 0x10 /* reserved pin 2 */ #define BPP_V3_PIN 0x20 /* reserved pin 3 */ #define BPP_ERR_PIN 0x01 /* Error pin */ #define BPP_SLCT_PIN 0x02 /* Select pin */ #define BPP_PE_PIN 0x04 /* Paper empty pin */

This structure is defined in the include file <sys/bpp_io.h>.

struct bpp_error_status { char timeout_occurred; /* 1 if a timeout occurred */ char bus_error; /* 1 if an SBus bus error */ uchar_t pin_status; /* * status of pins which could * cause an error */ }; /* Values for pin_status field */ #define BPP_ERR_ERR 0x01 /* Error pin active */ #define BPP_SLCT_ERR 0x02 /* Select pin active */ #define BPP_PE_ERR 0x04 /* Paper empty pin active */ #define BPP_SLCTIN_ERR 0x10 /* Select in pin active */ #define BPP_BUSY_ERR 0x40 /* Busy pin active */