:PROPERTIES: :ID: f1434d6f-fa94-4f5e-af19-9f27df023821 :mtime: 20240316062100 :ctime: 20240316062058 :END: #+title: polling #+filetags: :public:operatingsystems:project: * Polling Polling is a type of protocol for communication between an IO Device and a [[id:43419046-076d-4a73-b854-37054293a1f4][device driver.]] ** Steps for polling 1. The driver repeatedly reads the busy bit until that bit becomes ready. 2. The driver sets the write bit in the command register and writes a byte into the data-out register. 3. The driver sets the command-ready bit to true. 4. When the device notices that the command-ready bit is set, it sets the busy bit. 5. The device reads the command register and sees the write command. It reads the data-out register to get the byte and does the I/O to the device. 6. The controller clears the command-ready bit, clears the error bit in the status register to indicate that the device I/O succeeded, and clears the busy bit to indicate that it is finished.