zephyr: Allow to have per-board Zephyr config fragments.

To enable options which may be incompatible with other boards, etc.

zephyr/Makefile

@@ -62,7 +62,7 @@ CFLAGS = $(KBUILD_CFLAGS) $(NOSTDINC_FLAGS) $(ZEPHYRINCLUDE) \
 
 include ../py/mkrules.mk
 
-$(Z_EXPORTS):
+$(Z_EXPORTS): $(CONF_FILE)
 	$(MAKE) -f Makefile.zephyr BOARD=$(BOARD) CONF_FILE=$(CONF_FILE) initconfig outputexports
 
 GENERIC_TARGETS = all zephyr qemu qemugdb flash debug
@@ -95,3 +95,8 @@ clean: z_clean
 
 z_clean:
 	$(MAKE) -f Makefile.zephyr BOARD=$(BOARD) clean
+
+.PHONY: prj.conf
+prj.conf: prj_base.conf
+	cat $< >$@
+	if [ -f prj_$(BOARD).conf ]; then cat prj_$(BOARD).conf >>$@; fi

zephyr/prj.conf → zephyr/prj_base.conf

@@ -10,10 +10,3 @@ CONFIG_NETWORKING=y
 CONFIG_NET_IPV4=y
 CONFIG_TEST_RANDOM_GENERATOR=y
 CONFIG_NET_NBUF_RX_COUNT=4
-
-# Networking drivers
-# SLIP driver for QEMU
-CONFIG_NET_SLIP_TAP=y
-
-# BOARD-specific config (qemu_x86)
-CONFIG_RAM_SIZE=256

zephyr/prj_qemu_x86.conf

+# Networking drivers
+# SLIP driver for QEMU
+CONFIG_NET_SLIP_TAP=y
+
+# Default RAM easily overflows with uPy and networking
+CONFIG_RAM_SIZE=256