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Dedicated GPIO

:link_to_translation:zh_CN:[中文]

Overview

The dedicated GPIO is designed for CPU interaction with GPIO matrix and IO MUX. Any GPIO that is configured as "dedicated" can be access by CPU instructions directly, which makes it easy to achieve a high GPIO flip speed, and simulate serial/parallel interface in a bit-banging way. As toggling a GPIO in this "CPU Dedicated" way costs few overhead, it would be great for cases like performance measurement using an oscilloscope.

Create/Destroy GPIO Bundle

A GPIO bundle is a group of GPIOs, which can be manipulated at the same time in one CPU cycle. The maximal number of GPIOs that a bundle can contain is limited by each CPU. What's more, the GPIO bundle has a strong relevance to the CPU which it derives from. Any operations on the GPIO bundle should be put inside a task which is running on the same CPU core to the GPIO bundle belongs to. Likewise, only those ISRs who are installed on the same CPU core are allowed to do operations on that GPIO bundle.

Note

Dedicated GPIO is more of a CPU peripheral, so it has a strong relationship with CPU core. It's highly recommended to install and operate GPIO bundle in a pin-to-core task. For example, if GPIOA is connected to CPU0, and the dedicated GPIO instruction is issued from CPU1, then it's impossible to control GPIOA.

To install a GPIO bundle, one needs to call :cppdedic_gpio_new_bundle to allocate the software resources and connect the dedicated channels to user selected GPIOs. Configurations for a GPIO bundle are covered in :cppdedic_gpio_bundle_config_t structure:

  • :cppgpio_array: An array that contains GPIO number.
  • :cpparray_size: Element number of :cppgpio_array.
  • :cppflags: Extra flags to control the behavior of GPIO Bundle.
    • :cppin_en and :cppout_en are used to select whether to enable the input and output function (note, they can be enabled together).
    • :cppin_invert and :cppout_invert are used to select whether to invert the GPIO signal.

The following code shows how to install a output only GPIO bundle:

c

// configure GPIO
const int bundleA_gpios[] = {0, 1};
gpio_config_t io_conf = {
    .mode = GPIO_MODE_OUTPUT,
};
for (int i = 0; i < sizeof(bundleA_gpios) / sizeof(bundleA_gpios[0]); i++) {
    io_conf.pin_bit_mask = 1ULL << bundleA_gpios[i];
    gpio_config(&io_conf);
}
// Create bundleA, output only
dedic_gpio_bundle_handle_t bundleA = NULL;
dedic_gpio_bundle_config_t bundleA_config = {
    .gpio_array = bundleA_gpios,
    .array_size = sizeof(bundleA_gpios) / sizeof(bundleA_gpios[0]),
    .flags = {
        .out_en = 1,
    },
};
ESP_ERROR_CHECK(dedic_gpio_new_bundle(&bundleA_config, &bundleA));

To uninstall the GPIO bundle, one needs to call :cppdedic_gpio_del_bundle.

Note

:cppdedic_gpio_new_bundle doesn't cover any GPIO pad configuration (e.g., pull up/down, drive ability, output/input enable), so before installing a dedicated GPIO bundle, you have to configure the GPIO separately using GPIO driver API (e.g., :cppgpio_config). For more information about GPIO driver, please refer to GPIO API Reference <gpio>.

GPIO Bundle Operations

Operations Functions
Write to GPIOs in the bundle by mask :cppdedic_gpio_bundle_write
Read the value that output from the given GPIO bundle :cppdedic_gpio_bundle_read_out
Read the value that input to the given GPIO bundle :cppdedic_gpio_bundle_read_in

Note

Using the above functions might not get a high GPIO flip speed because of the overhead of function calls and the bit operations involved inside. Users can try manipulate_gpios_by_writing_assembly_code instead to reduce the overhead but should take care of the thread safety by themselves.

Manipulate GPIOs by Writing Assembly Code

For advanced users, they can always manipulate the GPIOs by writing assembly code or invoking CPU Low Level APIs. The usual procedure could be:

  1. Allocate a GPIO bundle: :cppdedic_gpio_new_bundle
  2. Query the mask occupied by that bundle: :cppdedic_gpio_get_out_mask or/and :cppdedic_gpio_get_in_mask
  3. Call CPU LL apis (e.g., dedic_gpio_cpu_ll_write_mask) or write assembly code with that mask

  4. The fastest way of toggling IO is to use the dedicated "set/clear" instructions:

    esp32s2 or esp32s3

    • Set bits of GPIO: set_bit_gpio_out imm[7:0]
    • Clear bits of GPIO: clr_bit_gpio_out imm[7:0]
    • Note: Immediate value width depends on the number of dedicated GPIO channels

    esp32c2 or esp32c3 or esp32c6 or esp32h2

    • Set bits of GPIO: csrrsi rd, csr, imm[4:0]
    • Clear bits of GPIO: csrrci rd, csr, imm[4:0]
    • Note: Can only control the lowest 4 GPIO channels

esp32s2

For details of supported dedicated GPIO instructions, please refer to {IDF_TARGET_NAME} Technical Reference Manual > IO MUX and GPIO Matrix (GPIO, IO_MUX) [PDF].

esp32s3

For details of supported dedicated GPIO instructions, please refer to {IDF_TARGET_NAME} Technical Reference Manual > Processor Instruction Extensions (PIE) (to be added later) [PDF].

not (esp32s2 or esp32s3)

For details of supported dedicated GPIO instructions, please refer to {IDF_TARGET_NAME} Technical Reference Manual > ESP-RISC-V CPU [PDF].

Some of the dedicated CPU instructions are also wrapped inside hal/dedic_gpio_cpu_ll.h as helper inline functions.

Note

Writing assembly code in application could make your code hard to port between targets, because those customized instructions are not guaranteed to remain the same format on different targets.

SOC_DEDIC_GPIO_HAS_INTERRUPT

Interrupt Handling

Dedicated GPIO can also trigger interrupt on specific input event. All supported events are defined in :cppdedic_gpio_intr_type_t.

One can enable and register interrupt callback by calling :cppdedic_gpio_bundle_set_interrupt_and_callback. The prototype of the callback function is defined in :cppdedic_gpio_isr_callback_t. Keep in mind, the callback should return true if there's some high priority task woken up.

c

// user defined ISR callback
IRAM_ATTR bool dedic_gpio_isr_callback(dedic_gpio_bundle_handle_t bundle, uint32_t index, void *args)
{
    SemaphoreHandle_t sem = (SemaphoreHandle_t)args;
    BaseType_t high_task_wakeup = pdFALSE;
    xSemaphoreGiveFromISR(sem, &high_task_wakeup);
    return high_task_wakeup == pdTRUE;
}

// enable positive edge interrupt on the second GPIO in the bundle (i.e., index 1)
ESP_ERROR_CHECK(dedic_gpio_bundle_set_interrupt_and_callback(bundle, BIT(1), DEDIC_GPIO_INTR_POS_EDGE, dedic_gpio_isr_callback, sem));

// wait for done semaphore
xSemaphoreTake(sem, portMAX_DELAY);

Application Example

* Software emulation (bit banging) of the UART/I2C/SPI protocols in assembly using the dedicated GPIOs and their associated CPU instructions: peripherals/dedicated_gpio. :SOC_DEDIC_GPIO_HAS_INTERRUPT: * Matrix keyboard example based on dedicated GPIO: peripherals/gpio/matrix_keyboard.

API Reference

inc/dedic_gpio.inc