Question

1. How does a system recover from errors?

2. Explain DMA operations.

Answer 1

1. There are different ways for a system to recover from errors. It also depends on the source of the error. One can sometimes need to remove the hardware recently added and start a repair session for the operating system. Usually the boot and restore will help in the recovery. Otherwise one can try to reinstall the operating system.

Whenever there is error in the system, the operating system looks for the cause of error, if it is file crashing, or some software issues, it tries to show a message on the screen to troubleshoot it.

2. DMA or direct memory access deals with a series of operations to be executed whenever required.

• Usually when the device needs to send data to another device or memory, a DMA request is sent to the controller.
• The controller then sends back an HRQ or hold request to the processor.
• Processor will then assert HLDA and data is tri-stated by the processor. Other buses such as control and address buses are offered the same treatment.
• The control by the CPU is left HLDA signal is issued to HOLD request.
• The CPU now goes into HOLD state.
• DMA takes over and manages the required operations using buses.