Fix heap without PSRAM. Never set heap_size.

ports/esp32s2/supervisor/port.c

@@ -59,8 +59,6 @@ void tick_timer_cb(void* arg) {
     supervisor_tick();
 }
 
-uint32_t* heap;
-
 safe_mode_t port_init(void) {
     esp_timer_create_args_t args;
     args.callback = &tick_timer_cb;
@@ -69,7 +67,7 @@ safe_mode_t port_init(void) {
     args.name = "CircuitPython Tick";
     esp_timer_create(&args, &_tick_timer);
 
-    heap = malloc(HEAP_SIZE);
+    heap = NULL;
     never_reset_module_internal_pins();
 
     #ifdef CONFIG_SPIRAM
@@ -81,6 +79,10 @@ safe_mode_t port_init(void) {
         heap = malloc(HEAP_SIZE);
         heap_size = HEAP_SIZE / sizeof(uint32_t);
     }
+    if (heap == NULL) {
+        return NO_HEAP;
+    }
+
     return NO_SAFE_MODE;
 }
 
@@ -142,13 +144,6 @@ supervisor_allocation* port_fixed_stack(void) {
     return &_fixed_stack;
 }
 
-supervisor_allocation _fixed_heap;
-supervisor_allocation* port_fixed_heap(void) {
-    _fixed_heap.ptr = port_heap_get_bottom();
-    _fixed_heap.length = (port_heap_get_top() - port_heap_get_bottom()) * sizeof(uint32_t);
-    return &_fixed_heap;
-}
-
 // Place the word to save just after our BSS section that gets blanked.
 void port_set_saved_word(uint32_t value) {
 }

supervisor/shared/safe_mode.c

@@ -133,6 +133,10 @@ void print_safe_mode_message(safe_mode_t reason) {
                 serial_write_compressed(translate("The CircuitPython heap was corrupted because the stack was too small.\nPlease increase the stack size if you know how, or if not:"));
                 serial_write_compressed(FILE_AN_ISSUE);
                 return;
+            case NO_HEAP:
+                serial_write_compressed(translate("CircuitPython was unable to allocate the heap.\n"));
+                serial_write_compressed(FILE_AN_ISSUE);
+                return;
             default:
                 break;
         }

supervisor/shared/safe_mode.h

@@ -42,6 +42,7 @@ typedef enum {
   FLASH_WRITE_FAIL,
   MEM_MANAGE,
   WATCHDOG_RESET,
+  NO_HEAP,
 } safe_mode_t;
 
 safe_mode_t wait_for_safe_mode_reset(void);