Digital

NAME

cxa − CXA16 communications interface

SYNOPSIS

controller dhu0 at uba0 csr 0160440 flags 0xffff vector dhurint dhuxint

DESCRIPTION

A CXA16 provides 16 data-leads-only communication lines with no modem control.  The CXA16 conforms to RS423A.  Each line attached to the CXA16 communications multiplexer behaves as described in tty(7) and can be set to run at any of 16 speeds; see tty(7) for the encoding. 

A flags field of 0xffff must be used to specify that all lines are to operate as hardwired. This is done to prevent the line from being treated as a modem control line. 

The dhu driver normally interrupts on each input character. 

Note

The cxa, cxb, and cxy devices operate under the control of the dhu driver. 

ERRORS

dhu%d: receive fifo overflow

The character input fifo overflowed before it could be serviced. This can happen if a hard error occurs when the CPU is running with elevated priority, as the system then prints a message on the console with interrupts disabled.  This can cause a few input characters to be lost to users.  It is not serious. 

dhu%d:%d DMA ERROR

A DMA transfer error has occurred.  The cxa unit number and line number are printed.  This means that the channel indicated has failed to transfer DMA data within 20 microseconds of the bus request being acknowledged or that there is a memory parity error.  This may cause a few output characters to be lost. 

dhu%d: DIAG. FAILURE

This indicates that the cxa internal diagnostics have detected an error. 

dhu%d: DHU HARDWARE ERROR. TX.DMA.START failed

The cxa failed to clear the start bit. Normally, this is cleared to signal that a DMA transfer has completed. 

FILES

/dev/tty??

RELATED INFORMAION

cxb(7), cxy(7), tty(7), MAKEDEV(8)