double_tap.c

#include <string.h>

#include <esp_system.h>
#include <esp32s3/rom/cache.h>

#include "double_tap.h"

#define NUM_TOKENS 3
static const uint32_t MAGIC_TOKENS[NUM_TOKENS] = {
    0xf01681de, 0xbd729b29, 0xd359be7a,
};

static void *magic_area;
static uint32_t backup_area[NUM_TOKENS];

#if ESP_IDF_VERSION >= ESP_IDF_VERSION_VAL(5, 0, 0)
// Current IDF does not map external RAM to a fixed address.
// The actual VMA depends on other enabled devices, so the precise
// location must be discovered.
#include <esp_psram.h>
#include <esp_private/esp_psram_extram.h>
static uintptr_t get_extram_data_high(void) {
    // get a pointer into SRAM area (only the address is useful)
    void *psram_ptr = heap_caps_malloc(16, MALLOC_CAP_SPIRAM);
    heap_caps_free(psram_ptr);

    // keep moving backwards until leaving PSRAM area
    uintptr_t psram_base_addr = (uintptr_t) psram_ptr;
    psram_base_addr &= ~(CONFIG_MMU_PAGE_SIZE - 1); // align to start of page
    while (esp_psram_check_ptr_addr((void *) psram_base_addr)) {
        psram_base_addr -= CONFIG_MMU_PAGE_SIZE;
    }

    // offset is one page from start of PSRAM
    return psram_base_addr + CONFIG_MMU_PAGE_SIZE + esp_psram_get_size();
}
#else
#include <soc/soc.h>
#define get_extram_data_high() ((uintptr_t) SOC_EXTRAM_DATA_HIGH)
#endif


void double_tap_init(void) {
    // magic location block ends 0x20 bytes from end of PSRAM
    magic_area = (void *) (get_extram_data_high() - 0x20 - sizeof(MAGIC_TOKENS));
}

void double_tap_mark() {
    memcpy(backup_area, magic_area, sizeof(MAGIC_TOKENS));
    memcpy(magic_area, MAGIC_TOKENS, sizeof(MAGIC_TOKENS));
    Cache_WriteBack_Addr((uintptr_t) magic_area, sizeof(MAGIC_TOKENS));
}

void double_tap_invalidate() {
    if (memcmp(backup_area, MAGIC_TOKENS, sizeof(MAGIC_TOKENS))) {
        // different contents: restore backup
        memcpy(magic_area, backup_area, sizeof(MAGIC_TOKENS));
    } else {
        // clear memory
        memset(magic_area, 0, sizeof(MAGIC_TOKENS));
    }
    Cache_WriteBack_Addr((uintptr_t) magic_area, sizeof(MAGIC_TOKENS));
}

bool double_tap_check_match() {
    return (memcmp(magic_area, MAGIC_TOKENS, sizeof(MAGIC_TOKENS)) == 0);
}