Guaranteed bandwidth allocation method in a computer system for input/output data transfers

In a computer system having a processing unit, a memory, a system controller and a plurality of peripheral devices coupled by a system bus, an apparatus for peer to peer data transmission comprising:

• means for defining a selected period of time as the granularity for transmission of data over the system bus;
• register means associated with said system controller and each of said peripheral devices for storing a respective programmable bandwidth counter value for each peripheral device;
• means for sequentially selecting each of said system controller and said peripheral devices having a bandwidth counter greater than a selected threshold and for establishing a peer-to-peer transmission path for uninterrupted guaranteed transmission of data during said selected period of time;
• register means associated with said system controller and each of said peripheral devices for storing a remainder weight value;
• and
• means for sequentially selecting said system controller and each of said peripheral devices having a bandwidth counter value less than said selected threshold and having data to be sent and for establishing a peer-to-peer transmission path for uninterrupted non-guaranteed transmission of data for up to a plurality of selected periods of time, where said plurality of selected periods of time correspond to the remainder weight value held in said register means.

A computer implemented method for enabling peer-to-peer communications among a plurality of peripherals coupled by a system bus in a computer system, each of said peripherals associated with an assigned sequential identification number, said method comprising the steps of:

• allocating the bandwidth of the system bus by defining a plurality of time slots for transmission of data between said peripherals;
• loading a respective programmable value, corresponding to a percentage of the allocated time slots, into a register associated with each of said peripherals having a requirement for transmitting data on a timely basis;
• sequentially, using a round robin selection, selecting a selected peripheral of said peripherals requesting transmission of data;
• determining if said value associated with said selected peripheral is greater than a selected threshold;
• transmitting data without interruption for a period of time corresponding to one time slot if said value in the register of the selected peripheral is greater than the selected threshold and decrementing said value in the register associated with said selected peripheral;
• repeating said selecting, determining, and transmitting steps until the values in each of said registers is less than the selected threshold or until said plurality of time slots have been used;
• and
• reloading said value into each of said registers and repeating said selecting, determining, transmitting, selecting and repeating steps;
• and
• loading a second register associated with each of said peripherals with a respective programmable value corresponding to a number of tokens for use in obtaining access to unused time slots in the event said registers associated with said peripherals are less than said selected threshold;
• selecting in a sequential round robin manner, peripherals having a value in said second register and transmission requests;
• and
• transmitting data to or from said selected peripheral without interruption for a period of time corresponding to a plurality of time slots where said plurality of time slots corresponds to the number of tokens loaded in said second register.

In a computer system having a processing unit coupled by a bus to a plurality of devices capable of exchanging data therebetween, a method of prioritizing the transfer of data comprising the steps of:

• a) allowing devices of a first priority ring to communicate, said step a) comprising the steps of:
• assigning said devices having real-time data transmissions to said first priority ring, said first priority ring having guaranteed access to a selectable portion of the available bandwidth of said bus;
• polling each device assigned to said first priority ring in a sequential round robin fashion to determine whether said polled device has data to transmit;
• transmitting said data without interruption from the polled device to a target device;
• and
• for each polled device allowed to transmit data, decreasing an associated respective programmable bandwidth allocation for said polled device;
• and
• b) provided communication of said devices of said first priority ring is complete, allowing devices of a second priority ring to communicate, said step b) comprising the steps of:
• assigning devices having non-real-time data transmissions to said second priority ring having access to the portion of said bandwidth not used by devices assigned to said first priority ring;
• polling each device assigned to said second priority ring in a sequential round robin fashion to determine whether said polled device has data to transmit;
• and
• transmitting said data without interruption from the polled device to a target device.