Lines Matching +full:system +full:- +full:on +full:- +full:chips

9 The documents in this directory give detailed instructions on how to access
17 A "General Purpose Input/Output" (GPIO) is a flexible software-controlled
18 digital signal. They are provided from many kinds of chips, and are familiar
20 represents a bit connected to a particular pin, or "ball" on Ball Grid Array
25 System-on-Chip (SOC) processors heavily rely on GPIOs. In some cases, every
26 non-dedicated pin can be configured as a GPIO; and most chips have at least
28 provide GPIOs; multifunction chips like power managers, and audio codecs
29 often have a few such pins to help with pin scarcity on SOCs; and there are
30 also "GPIO Expander" chips that connect using the I2C or SPI serial buses.
31 Most PC southbridges have a few dozen GPIO-capable pins (with only the BIOS
36   - Output values are writable (high=1, low=0). Some chips also have
38     value might be driven, supporting "wire-OR" and similar schemes for the
41   - Input values are likewise readable (1, 0). Some chips support readback
42     of pins configured as "output", which is very useful in such "wire-OR"
44     input de-glitch/debounce logic, sometimes with software controls.
46   - Inputs can often be used as IRQ signals, often edge triggered but
47     sometimes level triggered. Such IRQs may be configurable as system
48     wakeup events, to wake the system from a low power state.
50   - Usually a GPIO will be configurable as either input or output, as needed
53   - Most GPIOs can be accessed while holding spinlocks, but those accessed
56 On a given board each GPIO is used for one specific purpose like monitoring
57 MMC/SD card insertion/removal, detecting card write-protect status, driving
58 a LED, configuring a transceiver, bit-banging a serial bus, poking a hardware
59 watchdog, sensing a switch, and so on.
69 Active-High and Active-Low
70 --------------------------
76 being either active-high ("1" means "active", the default) or active-low ("0"
81 --------------------------
86 This is sometimes called a "wire-AND"; or more practically, from the negative
87 logic (low=true) perspective this is a "wire-OR".
89 One common example of an open drain signal is a shared active-low IRQ line.