NAME

bus − control of access to the system I/O bus

DESCRIPTION

Bus is a special file that controls a process’s access to the I/O space (segment 0xf) of the IBM RT PC or the PCIF map (segment 0xd) on the IBM 6152 Academic System.  Its use is usually associated with opening one of the bit-mapped display devices, when the user wants to read from or write to device control registers or display memory. 

Unlike /dev/kmem (mem(4)), which restricts memory accesses to reads and writes through a file descriptor, opening /dev/bus allows the process direct access to the 64KB of I/O addresses and the 16MB of memory addresses on the system I/O bus.  Closing /dev/bus removes these access rights. 

No other operations on /dev/bus are provided. 

NOTES

On the IBM 6152 Academic System, the I/O addresses are limited to those addresses used by display devices. 

FILES

/dev/bus

SEE ALSO

ibm5081(4), ibm5151(4), ibm6153(4), ibm6154(4), ibm6155(4), ibm8514(4), ibmaed(4), mem(4), vga(4)

BUGS

On the IBM RT PC, opening /dev/bus allows access to all devices on the system I/O bus. 
 

PRPQs 5799-WZQ/5799-PFF: IBM/4.3  —  Dec 1987