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| 16-device-drivers |
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Device controller and driver
driver Defn: a special kernel module that contrls the operations of a device with the device specific information controller Defn: a hardware unit on a device that can know and control a devices status or behaviour, which communicates with the CPU via a driver
Types of IO devices
- character stream vs block
- swqeuential vs random access
- synchronous vs async
- sharable or dedicated
OS provides a consistent interface for them in the /dev folder (unix systems). e.g., ramdisk device is name /dev/memdrv. each device has a file under /dev that can be handled with file operations read()/write()
block devices
commands (sent from device driver to device controller)
- read block
- write block
- seek block (for random access block devices)
the sequence of read/write requests can (should) be optimized
character devices
- commands
- get char
- put char
also support buffering (accepting keyboard input line by line) and editing of buffers (e.g., spcial treatement of backspace character)
IO models
IO system calls use different IO models
- blocking - when a proccess needs IO input it waits to recieve it before c
- non blocking
- async