esp8266: Set DEFPSIZE=1024, MINCACHE=3 for "btree" module.

Defaults of 4096 and 5 respectively are too high to esp8266, causing
out of memory with a database beyond couple of pages.

ports/esp8266/Makefile

@@ -7,6 +7,7 @@ MICROPY_PY_USSL = 1
 MICROPY_SSL_AXTLS = 1
 MICROPY_FATFS = 1
 MICROPY_PY_BTREE = 1
+BTREE_DEFS_EXTRA = -DDEFPSIZE=1024 -DMINCACHE=3
 
 FROZEN_DIR ?= scripts
 FROZEN_MPY_DIR ?= modules

py/py.mk

@@ -74,7 +74,7 @@ endif
 
 ifeq ($(MICROPY_PY_BTREE),1)
 BTREE_DIR = lib/berkeley-db-1.xx
-BTREE_DEFS = -D__DBINTERFACE_PRIVATE=1 -Dmpool_error=printf -Dabort=abort_ -Dvirt_fd_t=mp_obj_t "-DVIRT_FD_T_HEADER=<py/obj.h>"
+BTREE_DEFS = -D__DBINTERFACE_PRIVATE=1 -Dmpool_error=printf -Dabort=abort_ -Dvirt_fd_t=mp_obj_t "-DVIRT_FD_T_HEADER=<py/obj.h>" $(BTREE_DEFS_EXTRA)
 INC += -I$(TOP)/$(BTREE_DIR)/PORT/include
 SRC_MOD += extmod/modbtree.c
 SRC_MOD += $(addprefix $(BTREE_DIR)/,\