Enable PYSTACK to keep function state out of the heap

Author: tannewt

main.c

@@ -97,6 +97,10 @@ void do_str(const char *src, mp_parse_input_kind_t input_kind) {
     }
 }
 
+#if MICROPY_ENABLE_PYSTACK
+static size_t PLACE_IN_DTCM_BSS(_pystack)[CIRCUITPY_PYSTACK_SIZE / sizeof(size_t)];
+#endif
+
 void start_mp(supervisor_allocation* heap) {
     reset_status_led();
     autoreload_stop();
@@ -125,6 +129,10 @@ void start_mp(supervisor_allocation* heap) {
     // Clear the readline history. It references the heap we're about to destroy.
     readline_init0();
 
+    #if MICROPY_ENABLE_PYSTACK
+    mp_pystack_init(_pystack, _pystack + sizeof(_pystack));
+    #endif
+
     #if MICROPY_ENABLE_GC
     gc_init(heap->ptr, heap->ptr + heap->length / 4);
     #endif

py/circuitpy_mpconfig.h

@@ -119,6 +119,7 @@
 #define MICROPY_QSTR_BYTES_IN_HASH       (1)
 #define MICROPY_REPL_AUTO_INDENT         (1)
 #define MICROPY_REPL_EVENT_DRIVEN        (0)
+#define MICROPY_ENABLE_PYSTACK           (1)
 #define MICROPY_STACK_CHECK              (1)
 #define MICROPY_STREAMS_NON_BLOCK        (1)
 #ifndef MICROPY_USE_INTERNAL_PRINTF
@@ -785,6 +786,10 @@ void supervisor_run_background_tasks_if_tick(void);
 #define CIRCUITPY_FILESYSTEM_FLUSH_INTERVAL_MS 1000
 #endif
 
+#ifndef CIRCUITPY_PYSTACK_SIZE
+#define CIRCUITPY_PYSTACK_SIZE 1024
+#endif
+
 #define CIRCUITPY_BOOT_OUTPUT_FILE "/boot_out.txt"
 
 #define CIRCUITPY_VERBOSE_BLE 0