Bypass mechanism for daisy chain connected units

Claim 1

A bypass mechanism for improving operation of a daisy chain line linking a plurality of units and used for propagating a signal which may be trapped by a first unit in the chain having a pending service request to be serviced by a common resource, said daisy chain line being connected to the units through input means (56) and the signal to be propagated, if not trapped by the unit, being sent through output means (54) to a next unit in the chain, said mechanism allowing a desired maximum number x of distinct not contiguous sets comprising a variable number of contiguous units to be disconnected from the chain, and being characterized in that it comprises: x bidirectional lines (26) to which all units are attached, each unit having the capability to conditionally receive the signal to be propagated from said bidirectional lines and to conditionally provide the signal to be propagated to said bidirectional lines, control logic means (16, 12, 20) for identifying the sets of units, if any, which have to be disconnected from the daisy chain and sending bypass out control signals to the units preceding a first unit in each identified set and bypass in control signals to the units following a last unit in each identified set, said bypass out control signals and bypass in control signals being indicative of selected lines among the x bidirectional lines to be used for bypassing each identified set of units, first bypass control means (50, 70-1, 70-2) located in each unit and which are responsive to the bypass out control signal received from the control logic means to cause the signal to be propagated to be sent to the selected bidirectional line as indicated by the received bypass out control signal, second bypass control means (60,74-1, 74-2) located in each unit and responsive to the bypass control in signal received from the control logic means to cause the signal to be propagated along the chain to be received from the selected bidirectional line as indicated by the received bypass in control signal so as to bypass each set of units by means of a selected bidirectional line.