Usage of LittlevGL tasks in Micropython

gersch07 · January 26, 2020, 10:33am

Dear all,

I’m currently working on a small project, where a LittlevGL GUI in micropython should continuously refresh position data acquired by a UART GPS module (u-blox Neo-6m). My guess is that calling the “UART read” functions (which can take up to 400ms) would cause the GUI to be blocked during that time.
To circumvent this, I’ve tried to put the “UART read” (here: a dummy) function into a LittlevGL task, but haven’t had a success so far…
My (extremely basic) code looks like that:

#----------------------------- import packages -------------------------------

import lvgl as lv
import lvesp32
from time import sleep_ms

#------------- define a task that would, in a loop, block the GUI ------------

def some_blocking_function(data=None):
    print("Hello, I'll be blocking your GUI...")
    sleep_ms(300)

lv.init()
lv.task_core_init()
some_blocking_task = lv.task_create(some_blocking_function, 500, lv.TASK_PRIO.HIGH, None)
lv.task_enable(some_blocking_task)

#try:
while True:
    print("I'm not busy...")
    lv.task_handler()
    sleep_ms(100)

Does anyone have an idea what I’m doing wrong? It seems that my “some_blocking_task” is never called…
Thanks a lot for your help!

embeddedt · January 26, 2020, 12:58pm

A couple of issues I see:

Do not sleep in some_blocking_function. That will block the GUI for 300ms.
You do not need to call lv.task_core_init (as lv.init initializes everything for you here).
100ms is a pretty slow period to call lv.task_handler in. I would suggest calling it every 5-10 ms.
I don’t think calling lv.task_enable is needed either.

gersch07 · January 26, 2020, 3:18pm

Thanks for your suggestions! With them, the code executes both the loop and the task.
However, I’m afraid that achieving a responsive GUI that doesn’t block even if some readout function requires ~400 ms would require multithreading / something like freeRTOS…

EDIT: By the way, is it possible to implement features of the “uasyncio” library into the LittlevGL bindings? I really don’t have any idea how complicated this would be…

amirgon · January 26, 2020, 3:57pm

Did you try running your blocking readout function from another thread?

Under the hoods, a new micropython thread is actually a new FreeRTOS task:

github.com

micropython/micropython/blob/d89ed3e62b152174c3eb5c96713e9b983b11f7ed/ports/esp32/mpthreadport.c#L120-L140


void mp_thread_create_ex(void *(*entry)(void*), void *arg, size_t *stack_size, int priority, char *name) {
    // store thread entry function into a global variable so we can access it
    ext_thread_entry = entry;


    if (*stack_size == 0) {
        *stack_size = MP_THREAD_DEFAULT_STACK_SIZE; // default stack size
    } else if (*stack_size < MP_THREAD_MIN_STACK_SIZE) {
        *stack_size = MP_THREAD_MIN_STACK_SIZE; // minimum stack size
    }


    // Allocate linked-list node (must be outside thread_mutex lock)
    thread_t *th = m_new_obj(thread_t);


    mp_thread_mutex_lock(&thread_mutex, 1);


    // create thread
    BaseType_t result = xTaskCreatePinnedToCore(freertos_entry, name, *stack_size / sizeof(StackType_t), arg, priority, &th->id, MP_TASK_COREID);
    if (result != pdPASS) {
        mp_thread_mutex_unlock(&thread_mutex);
        mp_raise_msg(&mp_type_OSError, "can't create thread");
    }

amirgon · February 26, 2021, 12:21am

Example of LVGL + uasyncio:

github.com

lvgl/lv_binding_micropython/blob/master/examples/uasyncio_example1.py

##################################################################################################
#
# Example of LVGL with uasyncio event loop on unix and esp32 ports
#
# Running on Linux: (need micropython-dev for uasyncio):
#   ports/unix/micropython-dev -i lib/lv_bindings/examples/uasyncio_example1.py
#
#
##################################################################################################

# Workaround for including frozen modules when running micropython with a script argument
# https://github.com/micropython/micropython/issues/6419
import sys
sys.path.append("")

# Imports

from urandom import getrandbits, seed
from utime import ticks_us
from uasyncio import sleep, create_task, Loop

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