Memory controller for use with write-back cache system and multiple bus

Abstract

A computer system incorporating a memory controller which is capable of working with a write-back cache which operates using burst operations and with ISA and EISA bus masters. A state machine is provided for use with the cache controller and a state machine is provided for use with the EISA and ISA bus masters. When a bus master has requested data which is present only in the cache controller and a write-back operation must be performed, the memory controller halts the operation of the EISA and ISA bus masters until the data can be fully written back by the cache controller. In the case of an EISA bus master, this halting operation is performed by stretching the clocking signal which forms the synchronizing signal for the EISA bus. In the case of ISA bus masters, this halting is done by providing a wait state indication to the ISA bus masters. The state machine responsible for the memory controller cooperating with the bus masters is paused and the state machine for the cache controller is activated. The bus master state machine is paused until the cache controller state machine has completed all transfer operations and the data is fully contained in the main memory.