diff --git a/sw/.gitignore b/sw/.gitignore
index 6f30340..5a28233 100644
--- a/sw/.gitignore
+++ b/sw/.gitignore
@@ -1,5 +1,6 @@
 devicetree/devicetree.dtb
-buildroot_overlay/opt/
+buildroot_overlay/opt/puzzlefw/bin/puzzlecmd
+buildroot_overlay/opt/puzzlefw/driver/
 downloads/
 buildroot-2023.02.8/
 u-boot/
diff --git a/sw/buildroot_overlay/opt/puzzlefw/bin/puzzle-ipcfg b/sw/buildroot_overlay/opt/puzzlefw/bin/puzzle-ipcfg
new file mode 100755
index 0000000..48083ea
--- /dev/null
+++ b/sw/buildroot_overlay/opt/puzzlefw/bin/puzzle-ipcfg
@@ -0,0 +1,310 @@
+#!/bin/sh
+#
+# Manage IP address configuration.
+#
+# The IP address configuration exists in 3 places:
+#
+#  - The persistent configuration is stored in network.conf on
+#    the configuration partition of the SD card.
+#    This configuration is activated on boot.
+#
+#    The syntax of this file is as follows:
+#
+#      MODE=dhcp / MODE=static
+#      IPADDR=172.16.3.4
+#      NETMASK=255.255.0.0
+#      GATEWAY=172.16.0.1
+#
+#  - The active configuration, which determines the actual IP address,
+#    is stored in /var/lib/puzzlefw/cfg/network_active.conf in
+#    the RAM filesystem. It has the same format as described above.
+#
+#    The same information is also present in /etc/network/interfaces.
+#
+
+. /opt/puzzlefw/lib/functions.sh
+
+# Load the persistent or active configuration.
+#   $1 = file name to read
+load_network_config() {
+
+    if [ ! -f ${CONFIG_DIR}/${1} ]; then
+        echo "ERROR: File not found ${CONFIG_DIR}/${1}" >&2
+        exit 1
+    fi
+
+    . ${CONFIG_DIR}/${1}
+}
+
+# Write configuration to file.
+#   $1 = file name to write
+write_network_config() {
+
+    mkdir -p ${CONFIG_DIR}
+
+    cat >${CONFIG_DIR}/${1} <<EOF
+MODE=${MODE}
+IPADDR=${IPADDR}
+NETMASK=${NETMASK}
+GATEWAY=${GATEWAY}
+EOF
+}
+
+# Write /etc/network/interfaces
+write_network_interfaces() {
+
+    IF_METHOD="dhcp"
+    IF_ADDRESS=""
+    IF_NETMASK=""
+    IF_GATEWAY=""
+
+    if [ "$MODE" = "static" ]; then
+        IF_METHOD="static"
+        IF_ADDRESS="    address ${IPADDR}"
+	IF_NETMASK="    netmask ${NETMASK}"
+        if [ -n "$GATEWAY" ]; then
+            IF_GATEWAY="    gateway ${GATEWAY}"
+        fi
+    fi
+
+    echo "Writing /etc/network/interfaces ..."
+    cat >/etc/network/interfaces.new <<EOF
+
+auto lo
+iface lo inet loopback
+
+auto eth0
+iface eth0 inet $IF_METHOD
+$IF_ADDRESS
+$IF_NETMASK
+$IF_GATEWAY
+EOF
+
+    mv /etc/network/interfaces.new /etc/network/interfaces
+}
+
+# Initialize configuration from SD card.
+ipcfg_init() {
+
+    echo "Loading IP address configuration from SD card ..."
+
+    # Copy configuration from SD card.
+    lock_config || exit 1
+    read_config || exit 1
+
+    # Copy persistent configuration to active configuration.
+    cp -a ${CONFIG_DIR}/network.conf ${CONFIG_DIR}/network_active.conf
+
+    # Load persistent configuration.
+    load_network_config network.conf
+
+    # Write /etc/network/interfaces
+    write_network_interfaces
+}
+
+# Show loaded network configuration.
+show_network_config() {
+    echo "    Mode:       $MODE"
+    if [ "$MODE" = "static" ]; then
+        echo "    IP address: $IPADDR"
+        echo "    Netmask:    $NETMASK"
+        echo "    Gateway:    $GATEWAY"
+    fi
+}
+
+# Display configuration.
+ipcfg_show() {
+
+    load_network_config network_active.conf
+    echo "Active IP address configuration:"
+    show_network_config
+
+    load_network_config network.conf
+    echo "Saved IP address configuration:"
+    show_network_config
+}
+
+# Check that parameter is a well-formed IPv4 address.
+check_ipaddr() {
+    IFS="." read a b c d <<EOF
+$1
+EOF
+    for i in "$a" "$b" "$c" "$d" ; do
+        if ! [ "$i" -ge 0 -a "$i" -le 255 ]; then
+            echo "ERROR: Invalid IP address '$1'" >&2
+            exit 1
+        fi
+    done
+}
+
+# Check that parameter is a valid IPv4 netmask.
+check_netmask() {
+    IFS="." read a b c d <<EOF
+$1
+EOF
+    netmask_force_zero=0
+    for i in "$a" "$b" "$c" "$d" ; do
+        if [ "$netmask_force_zero" = "1" -a "$i" != "0" ]; then
+            echo "ERROR: Invalid netmask '$1'" >&2
+            exit 1
+        fi
+        if [ "$i" != "255" ]; then
+            netmask_force_zero=1
+            netmask_ok=0
+            for k in 254 252 248 240 224 192 128 0 ; do
+                if [ "$i" = "$k" ]; then
+                    netmask_ok=1
+                fi
+            done
+	    if [ "$netmask_ok" != "1" ]; then
+                echo "ERROR: Invalid netmask '$1'" >&2
+                exit 1
+            fi
+        fi
+    done
+}
+
+# Parse IP address options.
+parse_options() {
+
+    while [ -n "$1" ]; do
+
+        case "$1" in
+
+          --mode)
+            if [ "$2" != "dhcp" -a "$2" != "static" ]; then
+                echo "ERROR: Unknown mode '$2'" >&2
+                exit 1
+            fi
+            MODE="$2"
+            ;;
+
+          --ipaddr)
+            check_ipaddr "$2"
+            IPADDR="$2"
+            ;;
+
+          --netmask)
+            check_netmask "$2"
+            NETMASK="$2"
+            ;;
+
+          --gateway)
+            [ -z "$2" ] || check_ipaddr "$2"
+            GATEWAY="$2"
+            ;;
+
+          *)
+            echo "ERROR: Unknown option '$1'" >&2
+            exit 1
+        esac
+
+        shift 2
+    done
+
+    if [ -z "$MODE" ]; then
+        echo "ERROR: Missing mode" >&2
+        exit 1
+    fi
+
+    if [ "$MODE" = "static" ]; then
+        if [ -z "$IPADDR" ]; then
+            echo "ERROR: Missing IP address" >&2
+            exit 1
+        fi
+        if [ -z "$NETMASK" ]; then
+            echo "ERROR: Missing netmask" >&2
+            exit 1
+        fi
+    else
+        IPADDR=""
+	NETMASK=""
+	GATEWAY=""
+    fi
+}
+
+# Change active IP address configuration.
+ipcfg_config() {
+
+    # Lock to avoid conflicting changes.
+    lock_config || exit 1
+
+    echo "Changing active IP address configuration ..."
+
+    write_network_config network_active.conf.new
+    mv ${CONFIG_DIR}/network_active.conf.new ${CONFIG_DIR}/network_active.conf
+
+    echo "Shutting down eth0 ..."
+    /sbin/ifdown eth0
+    sleep 2
+
+    write_network_interfaces
+
+    echo "Starting eth0 ..."
+    /sbin/ifup eth0 || exit 1
+}
+
+# Change the persistent IP address configuration on the SD card.
+ipcfg_save() {
+
+    # Lock to avoid conflicting changes.
+    lock_config || exit 1
+
+    echo "Changing saved IP address configuration ..."
+
+    write_network_config network.conf.new || exit 1
+    sync_config network.conf || exit 1
+}
+
+case "$1" in
+  init)
+    ipcfg_init
+    ;;
+  show)
+    ipcfg_show
+    ;;
+  config)
+    shift
+    parse_options "$@"
+    ipcfg_config
+    ;;
+  save)
+    shift
+    parse_options "$@"
+    ipcfg_save
+    ;;
+  *)
+    cat <<EOF
+Usage: $0 {init|show|config|save|restart}
+
+Manage IP address configuration.
+
+  $0 init
+    Initialize IP address from saved configuration on SD card.
+    This command is used during boot and should not be invoked manually.
+
+  $0 show
+    Display active and saved IP address configuration.
+
+  $0 config {options}
+    Change active IP address configuration.
+    The new configuration is not written to the SD card.
+
+    options:
+      --mode dhcp           Enable configuration via DHCP.
+      --mode static         Enable static IP address configuration.
+      --ipaddr n.n.n.n      Specify static IPv4 address.
+      --netmask n.n.n.n     Specify netmask.
+      --gateway n.n.n.n     Specify gateway address, or "" to disable gateway.
+
+  $0 save {options}
+    Change the saved IP address configuration on the SD card.
+    Options are the same as for command 'config'.
+
+EOF
+    exit 1
+    ;;
+esac
+
+exit $?
+
diff --git a/sw/buildroot_overlay/opt/puzzlefw/lib/functions.sh b/sw/buildroot_overlay/opt/puzzlefw/lib/functions.sh
new file mode 100644
index 0000000..2a2ab2b
--- /dev/null
+++ b/sw/buildroot_overlay/opt/puzzlefw/lib/functions.sh
@@ -0,0 +1,63 @@
+#
+# Settings and functions for shell scripts.
+#
+
+CONFIG_PARTITION=mmcblk0p2
+CONFIG_MOUNTPOINT=/mnt/cfg
+CONFIG_DIR=/var/lib/puzzlefw/cfg
+
+# Lock the configuration files.
+lock_config() {
+
+    # Make config directory in RAM filesystem.
+    mkdir -p $CONFIG_DIR
+
+    # Create or open lock file.
+    # The file remains open until the calling script ends.
+    exec 3>>${CONFIG_DIR}/lockfile
+
+    # Get exclusive lock on the file.
+    if ! flock -n 3 ; then
+        echo "ERROR: Configuration locked" >&2
+        return 1
+    fi
+}
+
+# Read configuration files from the SD card.
+# This is only used during boot.
+read_config() {
+
+    # Mount config filesystem read-only.
+    mkdir -p $CONFIG_MOUNTPOINT
+    mount -t ext4 -r -o noatime,data=journal /dev/${CONFIG_PARTITION} $CONFIG_MOUNTPOINT || return 1
+
+    # Copy config files to RAM filesystem.
+    cp -a ${CONFIG_MOUNTPOINT}/*.conf $CONFIG_DIR
+
+    umount $CONFIG_MOUNTPOINT
+}
+
+# Write changed configuration files to the SD card.
+# Parameters: names of config files to synchronize
+sync_config() {
+
+    # Mount config filesystem.
+    mkdir -p $CONFIG_MOUNTPOINT
+    mount -t ext4 -o noatime,data=journal /dev/${CONFIG_PARTITION} $CONFIG_MOUNTPOINT || return 1
+
+    for fname in "$@" ; do
+
+        # Copy new version of file to SD card.
+        cp ${CONFIG_DIR}/${fname}.new $CONFIG_MOUNTPOINT
+
+	# Atomically replace the old file on the SD card.
+	mv ${CONFIG_MOUNTPOINT}/${fname}.new ${CONFIG_MOUNTPOINT}/${fname}
+
+	# Replace the old file in te RAM filesystem.
+	mv ${CONFIG_DIR}/${fname}.new ${CONFIG_DIR}/${fname}
+    done
+
+    umount $CONFIG_MOUNTPOINT
+    sync
+}
+