CODEWITHSUNDEEP
linuxgpio
surendra nath
surendra nath

Reputation: 339

Why all the pins on a chip are not GPIOs?

Documentation of GPIOs in Linux states:

A "General Purpose Input/Output" (GPIO) is a flexible software-controlled digital signal. They are provided from many kinds of chip, and are familiar to Linux developers working with embedded and custom hardware.

If we are capable of control the behavior of a pin, then why all the pins on a chip are not GPIOs?

OR

How can we provide functionality through software for a pin on chip?

Please explain.

Upvotes: 0

Views: 320

Answers (2)

JairoV
JairoV

Reputation: 2094

When you design an integrated circuit (chip) you design with some component model in mind, those internal components may have specific needs that can not be reassigned among different pins, then those pins are fixed function.

For example pins related to memory controller have a very strict performance requirements set (in terms of signal integrity, toggle rate, output driver, capacitance), those pins are fixed function not reassignable, thus you can not use those pins for GPIO. If you do it you will end with a slower chip because the additional circuit change those values becoming unfeasible. Other example are power domain pins (those tipically called VCC, VDD, VEE, GND,).

Thats why GPIO pins are always shared with slow interfaces like SPI, I2C, SMBUS but never with fast interfaces like SATA, DDR, etc.

In other cases the only reason is because the chip doesnt make sense without a particular component, for example, given you must to have RAM memory, then RAM dedicated pins doesnt need to be reassignable because you never will implement the system without RAM memory and never will need reuse those pins for GPIO

Upvotes: 3

Rajeshkumar
Rajeshkumar

Reputation: 798

All the pins in SOC are not GPIO. A specific group of pins mapped as GPIO. Other pins are configured for specific interfaces like DDR, SPI, I2C... etc, which includes clock, data and power supply pins. GPIO is generic pins can be used for any purpose based on user requirement. It can be used for handling IRQs, trigger Resets, Glow LEDs..etc.

for example, Consider a FPGA is connected to SOC via GPIOs. User need to program the FPGA via these GPIO pins. In SOC side user need to write a specific program with mentioned sequence to drive those GPIO to program the FPGA config file.

Upvotes: 1

Related Questions