I/O priority control — daisy chaining: Which of the following is NOT a characteristic of a daisy-chain priority control scheme for multiple devices?

Introduction / Context:
Daisy-chain priority is a classic hardware scheme for servicing interrupts or bus requests from multiple peripherals. The devices are physically chained so that request/grant signals propagate in order, giving a fixed hardware priority from the head to the tail of the chain.

Given Data / Assumptions:

• Devices are connected in a linear chain for request/grant propagation.
• Signals pass through each device to the next, establishing priority by physical position.
• We are identifying a statement that does not reflect this scheme’s characteristics.

Concept / Approach:

In daisy chaining, priority is inherently positional and therefore fixed by wiring order, not dynamically programmable. The wiring can simplify control-line count since a single grant line can be passed device-to-device. However, a device failure can block downstream devices, a known drawback.

Step-by-Step Solution:

Verification / Alternative check:

Bus standards and textbooks describe daisy chains as having static priority without additional logic; programmable priority requires separate controllers or software schemes.

Why Other Options Are Wrong:

• Easy to add devices: Generally true by extending the chain.
• Failure of one device may affect others: True—signals may not propagate past a failed device.
• Control lines independent of device count: Largely true; the same grant chain is reused.
• None of the above: Incorrect because one option is indeed not a characteristic.

Common Pitfalls:

Assuming “programmable” priority just because firmware exists; ignoring the reliability trade-off of chained propagation.

Final Answer:

priority is programmable