ESP32: Micropython allocated heap is reduced for IDF >= 4.2.2.

[glenn20]

Micropython allocates a heap size of only 65536 bytes on the ESP32 for later versions of the ESP IDF (>= 4.2.2) instead of the actually available 110536 bytes.

Since the implementationof a new allocator in the IDF (October 2020), heap_cap_get_largest_block() returns the size of the largest allocatable block rounded down to the nearest power of 2 (in contradiction with the documentation.

I have filed an issue against the IDF at espressif/esp-idf#7808.

The follwing patch provides an ugly work around:

diff --git a/ports/esp32/main.c b/ports/esp32/main.c
index 2ba613668..dce82b7fb 100644
--- a/ports/esp32/main.c
+++ b/ports/esp32/main.c
@@ -131,7 +131,20 @@ void mp_task(void *pvParameter) {
     #else
     // Allocate the uPy heap using malloc and get the largest available region
     size_t mp_task_heap_size = heap_caps_get_largest_free_block(MALLOC_CAP_8BIT);
-    void *mp_task_heap = malloc(mp_task_heap_size);
+    void *mp_task_heap;
+    for (size_t incr = mp_task_heap_size >> 1;
+         incr > 4;
+         incr >>= 1)
+    {
+        mp_task_heap_size += incr;
+        mp_task_heap = heap_caps_malloc(mp_task_heap_size, MALLOC_CAP_8BIT);
+        if (mp_task_heap == NULL) {
+            mp_task_heap_size -= incr;
+        }
+        heap_caps_free(mp_task_heap);
+        printf("HeapSize=0x%x  %d\n", mp_task_heap_size, mp_task_heap_size);
+    }
+    mp_task_heap = malloc(mp_task_heap_size);
     #endif
 
 soft_reset:

[IhorNehrutsa]

Correspond to ESP32: RAM leak in ESP-IDF v4.3 #7813

[glenn20]

A fix for this bug is in progress from Espressif (and appears to have landed in 4.3-dev - thanks @IhorNehrutsa) and once it arrives the memory allocated to gc heap on ESP32S2 will increase from 128kB to 157kB on the GENERIC_S2 target - exacerbating the issues on ESP32S2.

I have submitted PR #7963 to set a configurable limit on the amount of RAM micropython allocates to the heap.