build: MICROPY_FLOAT_IMPL

original PR:
pycom#470

Implement make option MICROPY_FLOAT_IMPL on Pycom/ESP32, so it is simpler to build Pycom/ESP32 firmware with single or double precision float point numbers. For example :
[esp32]$ make -j8 MICROPY_FLOAT_IMPL=double
instead of changing the 'esp32/mpconfigport.h', line :
#define MICROPY_FLOAT_IMPL (MICROPY_FLOAT_IMPL_FLOAT)
to
#define MICROPY_FLOAT_IMPL (MICROPY_FLOAT_IMPL_DOUBLE)
Batch scripts to build many Pycom/ESP32 firmware variants with combinations of boards (WIPY LOPY SIPY GPY FIPY LOPY4), single/double precision, etc, become possible.

In this way the Pycom/ESP32 building workflow becomes more compatible with MicroPython STM32 mainline workflow.

Author: peter-pycom

esp32/Makefile

@@ -144,6 +144,19 @@ CFLAGS_XTENSA_PSRAM = -mfix-esp32-psram-cache-issue -mfix-esp32-psram-cache-stra
 CFLAGS = $(CFLAGS_XTENSA) $(CFLAGS_XTENSA_PSRAM) $(CFLAGS_XTENSA_OPT) -nostdlib -std=gnu99 -g3 -ggdb -fstrict-volatile-bitfields -Iboards/$(BOARD)
 CFLAGS_SIGFOX = $(CFLAGS_XTENSA) -O2 -nostdlib -std=gnu99 -g3 -ggdb -fstrict-volatile-bitfields -Iboards/$(BOARD)
 
+# Configure floating point support
+ifeq ($(MICROPY_FLOAT_IMPL),double)
+CFLAGS += -DMICROPY_FLOAT_IMPL=MICROPY_FLOAT_IMPL_DOUBLE
+else
+ifeq ($(MICROPY_FLOAT_IMPL),none)
+CFLAGS += -DMICROPY_FLOAT_IMPL=MICROPY_FLOAT_IMPL_NONE
+else
+ifeq ($(MICROPY_FLOAT_IMPL),single)
+CFLAGS += -DMICROPY_FLOAT_IMPL=MICROPY_FLOAT_IMPL_FLOAT
+endif
+endif
+endif
+
 # These flags are used as per the output when linking examples/wifi/scan
 # -u ld_include_panic_highint_hdl is needed so esp32/dport_panic_panic_highint_hdl.S is linked and xt_highint4 is used from there,
 # otherwise xt_highint4 is used from freertos/xtensa/xtensa_vector_defaults.S which has incorrect implementation and results DPORT core lockup

esp32/mpconfigport.h

@@ -101,7 +101,9 @@
 #define MICROPY_PY_UTIMEQ                           (1)
 #define MICROPY_CPYTHON_COMPAT                      (1)
 #define MICROPY_LONGINT_IMPL                        (MICROPY_LONGINT_IMPL_MPZ)
+#ifndef MICROPY_FLOAT_IMPL   // can be configured by make option
 #define MICROPY_FLOAT_IMPL                          (MICROPY_FLOAT_IMPL_FLOAT)
+#endif
 #define MICROPY_ERROR_REPORTING                     (MICROPY_ERROR_REPORTING_NORMAL)
 #define MICROPY_OPT_COMPUTED_GOTO                   (1)
 #define MICROPY_OPT_CACHE_MAP_LOOKUP_IN_BYTECODE    (0)