diff --git a/README.md b/README.md
index aaf310b66..ed0f20091 100644
--- a/README.md
+++ b/README.md
@@ -86,8 +86,8 @@ Alternatively, fallback implementation based on setjmp/longjmp can be used.
 
 To build (see section below for required dependencies):
 
-    $ git submodule update --init
     $ cd ports/unix
+    $ make submodules
     $ make
 
 Then to give it a try:
@@ -127,13 +127,14 @@ Debian/Ubuntu/Mint derivative Linux distros, install `build-essential`
 Other dependencies can be built together with MicroPython. This may
 be required to enable extra features or capabilities, and in recent
 versions of MicroPython, these may be enabled by default. To build
-these additional dependencies, first fetch git submodules for them:
+these additional dependencies, in the port directory you're
+interested in (e.g. `ports/unix/`) first execute:
 
-    $ git submodule update --init
+    $ make submodules
 
-Use the same command to get the latest versions of dependencies, as
-they are updated from time to time. After that, in the port directory
-(e.g. `ports/unix/`), execute:
+This will fetch all the relevant git submodules (sub repositories) that
+the port needs.  Use the same command to get the latest versions of
+submodules as they are updated from time to time. After that execute:
 
     $ make deplibs
 
@@ -146,8 +147,8 @@ For example, to build SSL module (required for `upip` tool described above,
 and so enabled by dfeault), `MICROPY_PY_USSL` should be set to 1.
 
 For some ports, building required dependences is transparent, and happens
-automatically. They still need to be fetched with the git submodule command
-above.
+automatically.  But they still need to be fetched with the `make submodules`
+command.
 
 The STM32 version
 -----------------
@@ -159,8 +160,8 @@ https://launchpad.net/gcc-arm-embedded
 
 To build:
 
-    $ git submodule update --init
     $ cd ports/stm32
+    $ make submodules
     $ make
 
 You then need to get your board into DFU mode.  On the pyboard, connect the
diff --git a/ports/esp32/Makefile b/ports/esp32/Makefile
index 5d63a2586..2a752553e 100644
--- a/ports/esp32/Makefile
+++ b/ports/esp32/Makefile
@@ -38,6 +38,8 @@ FROZEN_MPY_DIR = modules
 # include py core make definitions
 include $(TOP)/py/py.mk
 
+GIT_SUBMODULES = lib/berkeley-db-1.xx
+
 PORT ?= /dev/ttyUSB0
 BAUD ?= 460800
 FLASH_MODE ?= dio
diff --git a/ports/esp32/README.md b/ports/esp32/README.md
index 2c7351ee5..518cafb71 100644
--- a/ports/esp32/README.md
+++ b/ports/esp32/README.md
@@ -122,17 +122,10 @@ this repository):
 $ make -C mpy-cross
 ```
 
-The ESP32 port has a dependency on Berkeley DB, which is an external
-dependency (git submodule). You'll need to have git initialize that
-module using the commands:
-```bash
-$ git submodule init lib/berkeley-db-1.xx
-$ git submodule update
-```
-
 Then to build MicroPython for the ESP32 run:
 ```bash
 $ cd ports/esp32
+$ make submodules
 $ make
 ```
 This will produce binary firmware images in the `build/` subdirectory
diff --git a/ports/esp8266/Makefile b/ports/esp8266/Makefile
index 8cac07afc..030f39fa9 100644
--- a/ports/esp8266/Makefile
+++ b/ports/esp8266/Makefile
@@ -32,6 +32,8 @@ FROZEN_MPY_DIR ?= modules
 # include py core make definitions
 include $(TOP)/py/py.mk
 
+GIT_SUBMODULES = lib/axtls lib/berkeley-db-1.xx
+
 FWBIN = $(BUILD)/firmware-combined.bin
 PORT ?= /dev/ttyACM0
 BAUD ?= 115200
diff --git a/ports/nrf/Makefile b/ports/nrf/Makefile
index a8bd95cc6..62208525f 100644
--- a/ports/nrf/Makefile
+++ b/ports/nrf/Makefile
@@ -41,6 +41,8 @@ QSTR_DEFS = qstrdefsport.h $(BUILD)/pins_qstr.h
 # include py core make definitions
 include ../../py/py.mk
 
+GIT_SUBMODULES = lib/nrfx lib/tinyusb
+
 MICROPY_FATFS ?= 0
 FATFS_DIR = lib/oofatfs
 MPY_CROSS = ../../mpy-cross/mpy-cross
diff --git a/ports/nrf/README.md b/ports/nrf/README.md
index 1b9c2ec7f..3c177c705 100644
--- a/ports/nrf/README.md
+++ b/ports/nrf/README.md
@@ -50,11 +50,11 @@ Prerequisite steps for building the nrf port:
 
     git clone <URL>.git micropython
     cd micropython
-    git submodule update --init
     make -C mpy-cross
 
 By default, the PCA10040 (nrf52832) is used as compile target. To build and flash issue the following command inside the ports/nrf/ folder:
 
+    make submodules
     make
     make flash
 
diff --git a/ports/samd/Makefile b/ports/samd/Makefile
index 77a53bd48..23646a484 100644
--- a/ports/samd/Makefile
+++ b/ports/samd/Makefile
@@ -19,6 +19,8 @@ QSTR_GLOBAL_DEPENDENCIES = $(BOARD_DIR)/mpconfigboard.h
 # Include py core make definitions
 include $(TOP)/py/py.mk
 
+GIT_SUBMODULES = lib/asf4 lib/tinyusb
+
 INC += -I.
 INC += -I$(TOP)
 INC += -I$(BUILD)
diff --git a/ports/stm32/Makefile b/ports/stm32/Makefile
index 28b90199a..112271fe1 100644
--- a/ports/stm32/Makefile
+++ b/ports/stm32/Makefile
@@ -24,6 +24,8 @@ FROZEN_MPY_DIR ?= modules
 # include py core make definitions
 include $(TOP)/py/py.mk
 
+GIT_SUBMODULES = lib/lwip lib/mbedtls lib/mynewt-nimble lib/stm32lib
+
 MCU_SERIES_UPPER = $(shell echo $(MCU_SERIES) | tr '[:lower:]' '[:upper:]')
 CMSIS_MCU_LOWER = $(shell echo $(CMSIS_MCU) | tr '[:upper:]' '[:lower:]')
 
diff --git a/ports/stm32/README.md b/ports/stm32/README.md
index a0c3b7ff3..f5ac362a8 100644
--- a/ports/stm32/README.md
+++ b/ports/stm32/README.md
@@ -40,7 +40,11 @@ see [here](https://launchpad.net/gcc-arm-embedded) for the main GCC ARM
 Embedded page.  The compiler can be changed using the `CROSS_COMPILE` variable
 when invoking `make`.
 
-To build for a given board, run:
+First the submodules must be obtained using:
+
+    $ make submodules
+
+Then to build for a given board, run:
 
     $ make BOARD=PYBV11
 
diff --git a/ports/unix/Makefile b/ports/unix/Makefile
index 41552bf5c..134502b4d 100644
--- a/ports/unix/Makefile
+++ b/ports/unix/Makefile
@@ -16,6 +16,8 @@ UNAME_S := $(shell uname -s)
 # include py core make definitions
 include $(TOP)/py/py.mk
 
+GIT_SUBMODULES = lib/axtls lib/berkeley-db-1.xx lib/libffi
+
 INC +=  -I.
 INC +=  -I$(TOP)
 INC += -I$(BUILD)
diff --git a/py/mkrules.mk b/py/mkrules.mk
index f9d77c317..a75c64db9 100644
--- a/py/mkrules.mk
+++ b/py/mkrules.mk
@@ -143,6 +143,13 @@ clean-prog:
 .PHONY: clean-prog
 endif
 
+submodules:
+	$(ECHO) "Updating submodules: $(GIT_SUBMODULES)"
+ifneq ($(GIT_SUBMODULES),)
+	$(Q)git submodule update --init $(addprefix $(TOP)/,$(GIT_SUBMODULES))
+endif
+.PHONY: submodules
+
 LIBMICROPYTHON = libmicropython.a
 
 # We can execute extra commands after library creation using