CSE 131 Lecture Notes - Lecture 18: Direct Memory Access, Electronic Component, Interrupt Handler
Document Summary
May be able to handle multiple devices. May be more than one controller per mechanical component. Convert serial bit stream to block of bytes. All memory accesses go over a shared bus. No need to specify device in advance. Name of a file or device is a string or an integer. Doesn"t depend on the machine (underlying hardware) Done as close to the hardware as possible. Most is asynchronous but blocking calls are easier. Data coming off a device cannot be stored in final destination. There are three ways an i/o can be performed: programmed i/o, interrupt driven i/o, i/o using dma. Checks if page is available and if it is, the printer will transfer one letter at a time while the user program is blocked. We cannot run another process while we wait. But, we need to process an interrupt routine for every character. I/o using dma frees the cpu to do anything until the job is done.
