Specifications

Device Driver Entry Points
Cloned UCB Routine
UCB$W_CHARGE(R2) Mailbox byte quota charge (UCB$W_SIZE)
UCB$W_REFC(R2) 0
UCB$L_STS(R2) UCB$V_DELETEUCB set, UCB$V_ONLINE set
UCB$W_DEVSTS(R2) UCB$V_DELMBX set if DEV$V_MBX is set in
UCB$L_DEVCHAR(R2)
UCB$L_OPCNT(R2) 0
UCB$L_SVAPTE(R2) 0
UCB$W_BOFF(R2) 0
UCB$W_BCNT(R2) 0
UCB$L_ORB(R2) Address of cloned ORB
ORB$L_OWNER
of template ORB
UIC of current process
ORB$L_ACL_MUTEX
of template ORB
FFFF
16
ORB$W_FLAGS
of template ORB
ORB$V_PROT_16 set
ORB$W_PROT
of template ORB
0
ORB$L_ACL_COUNT
of template ORB
0
ORB$L_ACL_DESC
of template ORB
0
ORB$R_MIN_CLASS
of template ORB
0 in first longword
Exit
A cloned UCB routine issues an RSB instruction to return control to
EXE$ASSIGN. If the routine returns error status in R0, EXE$ASSIGN undoes
the process of UCB cloning and completes with failure status in R0.
Description
When a process requests that a channel be assigned to a template device,
EXE$ASSIGN does not assign the channel to the template device itself. Rather,
it creates a copy of the template device’s UCB and ORB, initializing and clearing
certain fields as appropriate.
The driver’s cloned UCB routine verifies the contents of these fields and completes
their initialization.
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