Sending pointer to a struct through a queue in FreeRTOS - c

Question

I can't seem to figure out how to send a pointer to a struct using a queue in FreeRTOS. I've tried all I could think of, yet I always get a pointer to some random region of memory.
I'm trying to send a pointer to a button struct to another task, where it will then be drawn on the screen. I tried sending the whole object and it worked, but since there's a lot of data in the struct (data of two icons) I don't really want to do that.
The code is being run in Atmel SAME70 Xplained.
Here is a simpler version of the code I'm working on:
typedef struct {
uint32_t width;
uint32_t height;
uint32_t x;
uint32_t y;
uint8_t status;
void (*callback)(t_but);
tImage iconOn;
tImage iconOff;
} t_but;
void task_lcd(void) {
xQueueButtons = xQueueCreate(6, sizeof(struct t_but *));
t_but *button;
configure_lcd();
draw_screen();
while (1) {
if (xQueueReceive(xQueueButtons, &(button), (TickType_t)500 / portTICK_PERIOD_MS)) {
// This always prints some random numbers.
printf("Button X: %" PRIu32 "\r\n", button->x);
}
}
}
void task_buttons(void) {
t_but butPlay = {.width = 64,
.height = 64,
.x = 60,
.y = 445,
.status = 0,
.callback = &ButPlayCallback,
.iconOn = play_red,
.iconOff = play_black};
xQueueSend(xQueueButtons, &butPlay, 0);
while (1) {
// Some other code.
}
}
Any help is very much appreciated.

Answer 1

It appears from the API that the xQueueSend does a copy via the pointer passed so if you want to pass a pointer on the queue you need to pass the address of a pointer that is pointing at your structure.
void task_buttons(void) {
t_but butPlay = {.width = 64,
.height = 64,
.x = 60,
.y = 445,
.status = 0,
.callback = &ButPlayCallback,
.iconOn = play_red,
.iconOff = play_black};
t_but * const p_but = &butPlay;
xQueueSend(xQueueButtons, &p_but, 0);
while (1) {
// Some other code.
}
}