diff --git a/update_psa_impl b/update_psa_impl
new file mode 100755
index 0000000..90bbe87
--- /dev/null
+++ b/update_psa_impl
@@ -0,0 +1,117 @@
+# !/bin/bash -
+
+source ./general_utils
+source ./log_helpers
+source ./git_helpers
+source ./update_psa_helpers
+source ./read_config
+
+update_psa() {
+    local try_update_count=0
+    local func="${FUNCNAME[0]}"
+
+    # read config parameters
+    # read_config
+                
+    log_debug "$func:${LINENO}: fetch/merge updates..."
+   
+    # Fetch new updates (using git)
+    while :
+    do
+        local repository_is_already_up_to_date=""
+        if ! fetch_customer_updates repository_is_already_up_to_date; then
+            if [ "$repository_is_already_up_to_date" = "yes" ]; then
+                log_error "$func:${LINENO}: $customer_id is up-to-date"\
+                    "-> no files to update -> no psa update"
+                exit 1
+            fi
+            try_updates_count=$((try_updates_count+1))
+            if [[ "$try_updates_count" -eq 5 ]]; then
+                log_error "$func:${LINENO}: fetch/merging failed" ; exit 1
+            fi
+            sleep 60s
+        else
+            # Fetched updates successfully 
+            try_updates_count=0
+            break
+        fi
+    done
+
+    # TODO: backup implementieren
+    # Backup before any updates in case some previous test was wrong
+    if ! backup_previous_version; then
+        log_error "$func:${LINENO}: backup failed"
+        revert_customer_repository ; exit 1
+    fi
+
+    local changed_files=$(changed_file_names)
+    local conf_ini_files=$(filter_conf_ini_files "$changed_files")
+
+    # check if *.conf and/or *.ini-files have to md5-sum as denoted
+    # in update.conf
+    if ! check_md5_for_changed_conf_and_ini_files "$conf_ini_files" ; then
+        log_error "$func:${LINENO}: new customer files wrong"
+        revert_customer_repository ; exit 1
+    fi
+    
+    # copy *.conf and/or *.ini-files to their corresponding system-directories
+    if ! copy $conf_ini_files; then
+        log_error "$func:${LINENO}: copy operation failed"
+        revert_customer_repository ; exit 1
+    fi
+
+    # check if the opkg-command-file has been changed during 'git pull'
+    if grep -qE ".*opkg_commands.*?" <<< $changed_files; then
+        # read opkg_cmds: each line respresents an opkg-command
+        readarray opkg_commands < <(cat $opkg_cmds_file)
+        for opkg_c in "${opkg_commands[@]}"; do
+            if grep -qE "^\s*[#]+.*$" <<< $opkg_c; then
+                continue    # found comment line
+            fi
+
+            # package manipulation commands without package:
+            local cwp="update|upgrade|clean"
+            # informational commands without package:
+            cwp="${cwp}|list|list-installed|list-upgradable"
+
+            if grep -qE "^.*\s+($cwp)\s+.*$" <<< $opkg_c; then
+                local p=$(printf '%s' "$opkg_c" | awk '{ print $NF }')
+                local opkg_output=()
+                if ! exec_opkg_info "$p" opkg_output; then
+                    log_error "$func:${LINENO}: opkg info $opkg_c failed"
+                    revert_customer_repository ; exit 1
+                fi
+
+                if ! check_md5_for_opkg_packages opkg_output; then
+                    log_error "$func:${LINENO}: "\
+                        "wrong md5sum for opkg packages"
+                    revert_customer_repository ; exit 1
+                fi
+            fi
+            
+            # perform a dry-run and check if everything might work as expected. 
+            if ! exec_opkg_noaction $opkg_c; then
+                    log_error "$func:${LINENO}: "\
+                        "opkg --noaction $opkg_c failed"
+            fi
+
+            # Actually execute the opkg command
+            if ! exec_opkg $opkg_c; then
+                log_error "$func:${LINENO}: exec_opkg $opkg_c failed"
+                fallback_to_previous_version
+                revert_customer_repository ; exit 1
+            fi
+        done
+    else
+        log_info "$func:${LINENO}: no opkg commnds to execute"
+    fi
+    
+    # Cleanup.
+    if ! cleanup_previous_version; then
+        log_error "$func:${LINENO}: cleanup_previous_version failed"
+    fi
+            
+    log_info "$func:${LINENO}: success"
+    exit 0
+}
+