Abstract: An improved access control system for a memory system in which memory locations can be allocated to virtual output queues dedicated to output ports from the system. The virtual queues can be used to handle data of different priorities. Thresholds are defined for the occupancy of the overall memory and of each virtual queue. The access control system regulates the acceptance of data stored in input adapters by determining whether a back pressure situation exists for the data's target output adapter for the class of traffic to which the data belongs. A single-bit access-controlling back pressure signal is generated as a function of the occupancy level of either the overall memory or of the virtual queue defined for the target output adapter.

Abstract: This invention relates to a protocol implemented in a communication system for exchanging data and control messages between adapters to which are attached different users, and a shared memory subsystem comprising a depository storage, a manager of storage and a microprocessor. Such protocol enables the adapters to be the initiators of the transmission and reception of data by using the control lines that connect the manager of storage to all adapters in the same way as the data bus and the address bus. Moreover, the adapters slice the messages into data bursts to which are associated control words specifying the sizes, the owner and the position of the burst in the message. Consequently, those data bursts may be interleaved when transiting on the data bus without the intervention of the microprocessor for the routing, and they will be stored in or read from the depository storage according to the identification of the user in the control word.

Abstract: A hot plug circuit insuring that the plugging of cards to a board is performed in the hot-plug mode when the cards are supplied from a common power supply located on one of the cards or on the board. This circuit (62) limits the surge current generated at the interconnection of first circuits (30) arranged on a first card (1) and powered by a supply device (2) providing a first supply voltage (ground) on a first supply line (36) and a second supply voltage (+V) on a second supply line (34), with second circuit (24) on a second card powered by the supply device (2) through a third supply line (74) and fourth supply line (76). The surge current results from the charge of a decoupling capacitor of capacitance Cd arranged on the second card between the third and fourth supply lines when the cards are interconnected through an interconnecting arrangement (14, 12, 22).

Abstract: A Control Unit is described, including a Processing Unit (12) controlled by a Service Processor (14), and a plurality of adapters (18) exchanging data and/or control signals with said Processing Unit (PU). For ensuring a continuous operation of the Control Unit, the adapters are partitioned into at least two sets (56,58), and the PU is partitioned into at least two parts (26,28), each set of adapters being connected to a dedicated PU part by a primary bus (52,54). Besides, in order to allow the fallback of a set of adapters onto another PU part if the PU part to which it is normally connected is inoperative, a bus switching device (30) is provided. This bus switching device includes at least two Switch parts (38,40), and each Switch part performs the switching of a given set of adapters onto a given PU part, according to the status of each PU part.

Abstract: Adapter interfaces (ADAPT) and line driver interfaces (RDVP and RDVC) are divided into subgroups within a pyramid type of architecture. Each subgroup is provided with independent preselection means for determining the path through the pyramid from the CCU BUS to the adapter to be serviced first.