|  | Parallel Port Devices | 
|  | ===================== | 
|  |  | 
|  | .. kernel-doc:: include/linux/parport.h | 
|  | :internal: | 
|  |  | 
|  | .. kernel-doc:: drivers/parport/ieee1284.c | 
|  | :export: | 
|  |  | 
|  | .. kernel-doc:: drivers/parport/share.c | 
|  | :export: | 
|  |  | 
|  | .. kernel-doc:: drivers/parport/daisy.c | 
|  | :internal: | 
|  |  | 
|  | 16x50 UART Driver | 
|  | ================= | 
|  |  | 
|  | .. kernel-doc:: drivers/tty/serial/serial_core.c | 
|  | :export: | 
|  |  | 
|  | .. kernel-doc:: drivers/tty/serial/8250/8250_core.c | 
|  | :export: | 
|  |  | 
|  | Pulse-Width Modulation (PWM) | 
|  | ============================ | 
|  |  | 
|  | Pulse-width modulation is a modulation technique primarily used to | 
|  | control power supplied to electrical devices. | 
|  |  | 
|  | The PWM framework provides an abstraction for providers and consumers of | 
|  | PWM signals. A controller that provides one or more PWM signals is | 
|  | registered as :c:type:`struct pwm_chip <pwm_chip>`. Providers | 
|  | are expected to embed this structure in a driver-specific structure. | 
|  | This structure contains fields that describe a particular chip. | 
|  |  | 
|  | A chip exposes one or more PWM signal sources, each of which exposed as | 
|  | a :c:type:`struct pwm_device <pwm_device>`. Operations can be | 
|  | performed on PWM devices to control the period, duty cycle, polarity and | 
|  | active state of the signal. | 
|  |  | 
|  | Note that PWM devices are exclusive resources: they can always only be | 
|  | used by one consumer at a time. | 
|  |  | 
|  | .. kernel-doc:: include/linux/pwm.h | 
|  | :internal: | 
|  |  | 
|  | .. kernel-doc:: drivers/pwm/core.c | 
|  | :export: |