Bus contention
Encyclopedia
Bus contention, in computer design, is an undesirable state of the bus
in which more than one device on the bus attempts to place values on the bus at the same time. Most bus architectures require their devices follow an arbitration protocol carefully designed to make the likelihood of contention negligible. However, when devices on the bus have logic errors, manufacturing defects or are driven beyond their design speeds, arbitration may break down and contention may result. Contention may also arise on systems which have a programmable memory mapping
and when illegal values are written to the registers
controlling the mapping.
Contention can lead to erroneous operation, and in unusual cases, damage to the hardware—such as fusing of the bus wiring.
Bus contention is sometimes countered by buffering the output of memory-mapped devices. However, it has been noted that high impedance from one device will still interfere with the bus values of other devices. Currently, no standard solution exists for data-bus contention between memory devices, such as EEPROM and SRAM.
Computer bus
In computer architecture, a bus is a subsystem that transfers data between components inside a computer, or between computers.Early computer buses were literally parallel electrical wires with multiple connections, but the term is now used for any physical arrangement that provides the same...
in which more than one device on the bus attempts to place values on the bus at the same time. Most bus architectures require their devices follow an arbitration protocol carefully designed to make the likelihood of contention negligible. However, when devices on the bus have logic errors, manufacturing defects or are driven beyond their design speeds, arbitration may break down and contention may result. Contention may also arise on systems which have a programmable memory mapping
Memory mapping
In computing, memory mapping may refer to:* Memory-mapped file, also known as mmap* Memory-mapped I/O, an alternative to port I/O; a communication between CPU and peripheral device using the same instructions, and same bus, as between CPU and memory...
and when illegal values are written to the registers
Hardware register
In digital electronics, especially computing, a hardware register stores bits of information, in a way that all the bits can be written to or read out simultaneously.The hardware registers inside a central processing unit are called processor registers....
controlling the mapping.
Contention can lead to erroneous operation, and in unusual cases, damage to the hardware—such as fusing of the bus wiring.
Bus contention is sometimes countered by buffering the output of memory-mapped devices. However, it has been noted that high impedance from one device will still interfere with the bus values of other devices. Currently, no standard solution exists for data-bus contention between memory devices, such as EEPROM and SRAM.