GPIO HWIP Technical Specification

Overview

This document specifies GPIO hardware IP functionality. This module conforms to the Comportable guideline for peripheral device functionality See that document for integration overview within the broader top level system.

Features

• 32 GPIO ports
• Configurable interrupt per GPIO for detecting rising edge, falling edge, or active low/high input
• Two ways to update GPIO output: direct-write and masked (thread-safe) update

Description

The GPIO block allows software to communicate through general purpose I/O pins in a flexible manner. Each of 32 independent bits can be written as peripheral outputs in two modes. Each of the 32 bits can be read by software as peripheral inputs. How these peripheral inputs and outputs are connected to the chip IO is not within the scope of this document. See the Comportability Specification for peripheral IO options at the top chip level.

In the output direction, this module provides direct 32b access to each GPIO value using direct write. This mode allows software to control all GPIO bits simultaneously. Alternately, this module provides masked writes to half of the bits at a time, allowing software to affect the output value of a subset of the bits without requiring a read-modify-write. In this mode the user provides a mask of which of the 16 bits are to be modified, along with their new value. The details of this mode are given in the Programmers Guide below.

In the input direction, software can read the contents of any of the GPIO peripheral inputs. In addition, software can request the detection of an interrupt event for any of the 32 bits in a configurable manner. The choices are positive edge, negative edge or level detection events. A noise filter is available through configuration for any of the 32 GPIO inputs. This requires the input to be stable for 16 cycles of the module clock before the input register reflects the change and interrupt generation is evaluated. Note that if the filter is enabled and the pin is set to output then there will be a corresponding delay in a change in output value being reflected in the input register.

See the Design Details section for more details on output, input, and interrupt control.

Theory of Operations

Block Diagram

The block diagram above shows the DATA_OUT and DATA_OE registers managed by hardware outside of the auto-generated register file. For reference, it also shows the assumed connections to pads in the top level netlist.

Hardware Interfaces

Referring to the Comportable guideline for peripheral device functionality, the module gpio has the following hardware interfaces defined.

Primary Clock: clk_i

Other Clocks: none

Bus Device Interface: tlul

Bus Host Interface:

Peripheral Pins for Chip IO:

Interrupts:

Security Alerts: none

Design Details

GPIO Output logic

The GPIO module maintains one 32-bit output register DATA_OUT with two ways to write to it. Direct write access uses DIRECT_OUT, and masked access uses MASKED_OUT_UPPER and MASKED_OUT_LOWER. Direct access provides full write and read access for all 32 bits in one register.

For masked access the bits to modify are given as a mask in the upper 16 bits of the MASKED_OUT_UPPER and MASKED_OUT_LOWER register write, while the data to write is provided in the lower 16 bits of the register write. The hardware updates DATA_OUT with the mask so that the modification is done without software requiring a Read-Modify-Write.

Reads of masked registers return the lower/upper 16 bits of the DATA_OUT contents. Zeros are returned in the upper 16 bits (mask field). To read what is on the pins, software should read the DATA_IN register. (See GPIO Input section below).

The same concept is duplicated for the output enable register DATA_OE. Direct access uses DIRECT_OE, and masked access is available using MASKED_OE_UPPER and MASKED_OE_LOWER.

The output enable is sent to the pad control block to determine if the pad should drive the DATA_OUT value to the associated pin or not.

A typical use pattern is for initialization and suspend/resume code to use the full access registers to set the output enables and current output values, then switch to masked access for both DATA_OUT and DATA_OE.

For GPIO outputs that are not used (either not wired to a pin output or not selected for pin multiplexing), the output values are disconnected and have no effect on the GPIO input, regardless of output enable values.

GPIO Input

The DATA_IN register returns the contents as seen on the peripheral input, typically from the pads connected to those inputs. In the presence of a pin-multiplexing unit, GPIO peripheral inputs that are not connected to a chip input will be tied to a constant zero input.

The GPIO module provides optional independent noise filter control for each of the 32 input signals. Each input can be independently enabled with the CTRL_EN_INPUT_FILTER (one bit per input). This 16-cycle filter is applied to both the DATA_IN register and the interrupt detection logic. The timing for DATA_IN is still not instantaneous if CTRL_EN_INPUT_FILTER is false as there is top-level routing involved, but no flops are between the chip input and the DATA_IN register.

The contents of DATA_IN are always readable and reflect the value seen at the chip input pad regardless of the output enable setting from DATA_OE. If the output enable is true (and the GPIO is connected to a chip-level pad), the value read from DATA_IN includes the effect of the peripheral’s driven output (so will only differ from DATA_OUT if the output driver is unable to switch the pin or during the delay imposed if the noise filter is enabled).

Interrupts

The GPIO module provides 32 interrupt signals to the main processor. Each interrupt can be independently enabled, tested, and configured. Following the standard interrupt guidelines in the Comportability Specification, the 32 bits of the INTR_ENABLE register determines whether the associated inputs are configured to detect interrupt events. If enabled via the various INTR_CTRL_EN registers, their current state can be read in the INTR_STATE register. Clearing is done by writing a 1 into the associated INTR_STATE bit field.

For configuration, there are 4 types of interrupts available per bit, controlled with four control registers. INTR_CTRL_EN_RISING configures the associated input for rising-edge detection. Similarly, INTR_CTRL_EN_FALLING detects falling edge inputs. INTR_CTRL_EN_LVLHIGH and INTR_CTRL_EN_LVLLOW allow the input to be level sensitive interrupts. In theory an input can be configured to detect both a rising and falling edge, but there is no hardware assistance to indicate which edge caused the output interrupt.

Note #1: all inputs are sent through optional noise filtering before being sent into interrupt detection. Note #2: all output interrupts to the processor are level interrupts as per the Comportability Specification guidelines. The GPIO module, if configured, converts an edge detection into a level interrupt to the processor core.

Programmers Guide

Initialization

Initialization of the GPIO module includes the setting up of the interrupt configuration for each GPIO input, as well as the configuration of the required noise filtering. These do not provide masked access since they are not expected to be done frequently.

// enable inputs 0 and 1 for rising edge detection with filtering,
// inputs 2 and 3 for falling edge detection with filtering,
// input 4 for both rising edge detection (no filtering)
// and inputs 6 and 7 for active low interrupt detection
*GPIO_INTR_ENABLE =          0b11011111;
*GPIO_INTR_CTRL_EN_RISING =  0b00010011;
*GPIO_INTR_CTRL_EN_FALLING = 0b00011100;
*GPIO_INTR_CTRL_EN_LVLLOW  = 0b11000000;
*GPIO_INTR_CTRL_EN_LVLHIGH = 0b00000000;
*GPIO_CTRL_EN_INPUT_FILTER = 0b00001111;

Common Examples

This section below shows the interaction between the direct access and mask access for data output and data enable.

// assume all GPIO are connected to chip pads.
// assume a weak pullup on all pads, returning 1 if undriven.
printf("0x%x", *GPIO_DATA_IN);          // 0xffffffff

*DIRECT_OUT = 0x11223344;
printf("0x%x", *GPIO_DIRECT_OUT);       // 0x11223344

*DIRECT_OE  = 0x00ff00ff;
printf("0x%x", *GPIO_DIRECT_OE);        // 0x00ff00ff

// weak pullup still applies to undriven signals
printf("0x%x", *GPIO_DATA_IN);          // 0xff22ff44

// read of direct_out still returns DATA_OUT contents
printf("0x%x", *GPIO_DIRECT_OUT);       // 0x11223344

// try masked accesses to DATA_OUT
*GPIO_MASKED_OUT_LOWER = 0x0f0f5566
printf("0x%x", *GPIO_MASKED_OUT_LOWER); // 0x00003546
printf("0x%x", *GPIO_DIRECT_OUT);       // 0x11223546

*GPIO_MASKED_OUT_UPPER = 0x0f0f7788
printf("0x%x", *GPIO_MASKED_OUT_UPPER); // 0x00001728
printf("0x%x", *GPIO_DIRECT_OUT);       // 0x17283546

// OE still applies
printf("0x%x", *GPIO_DATA_IN);          // 0xff28ff46

// manipulate OE
*GPIO_DIRECT_OE = 0xff00ff00;
printf("0x%x", *GPIO_DIRECT_OE);        // 0xff00ff00
printf("0x%x", *GPIO_DATA_IN);          // 0x17ff35ff

*GPIO_MASKED_OE_LOWER = 0x0f0f0f0f;
printf("0x%x", *GPIO_MASKED_OE_LOWER);  // 0x00000f0f
printf("0x%x", *GPIO_DIRECT_OE);        // 0xff000f0f
printf("0x%x", *GPIO_DATA_IN);          // 0x17fff5f6

*GPIO_MASKED_OE_UPPER = 0x0f0f0f0f;
printf("0x%x", *GPIO_MASKED_OE_UPPER);  // 0x00000f0f
printf("0x%x", *GPIO_DIRECT_OE);        // 0x0f0f0f0f
printf("0x%x", *GPIO_DATA_IN);          // 0xf7f8f5f6

Interrupt Handling

This section below gives an example of how interrupt clearing works, assuming some events have occurred as shown in comments.

*INTR_ENABLE = 0x000000ff;              // interrupts enabled GPIO[7:0] inputs
printf("0b%x", *GPIO_DATA_IN);          // assume 0b00000000
printf("0b%x", *GPIO_INTR_STATE);       // 0b00000000

*INTR_CTRL_EN_RISING  = 0b00010001;     // rising detect on GPIO[0], GPIO[4]
*INTR_CTRL_EN_FALLING = 0b00010010;     // falling detect on GPIO[1], GPIO[4]
*INTR_CTRL_EN_LVLLOW  = 0b00001100;     // falling detect on GPIO[2], GPIO[3]
*INTR_CTRL_EN_LVLHIGH = 0b11000000;     // falling detect on GPIO[6], GPIO[7]

// already detected intr[3,2] (level low)
printf("0b%b", *GPIO_INTR_STATE);       // 0b00001100

// try and clear [3:2], fails since still active low
*GPIO_INTR_STATE = 0b00001100;
printf("0b%b", *GPIO_INTR_STATE);       // 0b00001100

// EVENT: all bits [7:0] rising, triggers [7,6,4,0], [3,2] still latched
printf("0b%b", *GPIO_DATA_IN);          // 0b11111111
printf("0b%b", *GPIO_INTR_STATE);       // 0b11011101

// try and clear all bits, [7,6] still detecting level high
*GPIO_INTR_STATE = 0b11111111;
printf("0b%b", *GPIO_INTR_STATE);       // 0b11000000

// EVENT: all bits [7:0] falling, triggers [4,3,2,1], [7,6] still latched
printf("0b%b", *GPIO_DATA_IN);          // 0b00000000
printf("0b%b", *GPIO_INTR_STATE);       // 0b11011110

// try and clear all bits, [3,2] still detecting level low
*GPIO_INTR_STATE = 0b11111111;
printf("0b%b", *GPIO_INTR_STATE);       // 0b00001100

// write test register for all 8 events, trigger regardless of external events
*GPIO_INTR_TEST = 0b11111111;
printf("0b%b", *GPIO_INTR_STATE);       // 0b11111111

// try and clear all bits, [3,2] still detecting level low
*GPIO_INTR_STATE = 0b11111111;
printf("0b%b", *GPIO_INTR_STATE);       // 0b00001100

Register Table