move vta.exec.rpc_server to new vta_onboard package

 * split the dependency away from vta package

apps/vta_rpc/start_rpc_server.sh

@@ -6,9 +6,9 @@
 # to you under the Apache License, Version 2.0 (the
 # "License"); you may not use this file except in compliance
 # with the License.  You may obtain a copy of the License at
-# 
+#
 #   http://www.apache.org/licenses/LICENSE-2.0
-# 
+#
 # Unless required by applicable law or agreed to in writing,
 # software distributed under the License is distributed on an
 # "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
@@ -19,4 +19,4 @@ PROJROOT="$( cd "$( dirname "${BASH_SOURCE[0]}" )/../../" && pwd )"
 
 export PYTHONPATH=${PYTHONPATH}:${PROJROOT}/python:${PROJROOT}/vta/python
 export PYTHONPATH=${PYTHONPATH}:/home/xilinx/pynq
-python3 -m vta.exec.rpc_server
+python3 -m vta_onboard.exec.rpc_server

apps/vta_rpc/start_rpc_server_to_tracker.sh

@@ -23,4 +23,4 @@ TARGET=$(python ${VTA_CONFIG} --target)
 
 export PYTHONPATH=${PYTHONPATH}:${PROJROOT}/python:${PROJROOT}/vta/python
 export PYTHONPATH=${PYTHONPATH}:/home/xilinx/pynq
-python3 -m vta.exec.rpc_server --tracker fleet:9190 --key $TARGET
+python3 -m vta_onboard.exec.rpc_server --tracker fleet:9190 --key $TARGET

vta/python/vta/__init__.py

@@ -20,6 +20,7 @@
 Besides the compiler toolchain, it also includes utility functions to
 configure the hardware environment and access remote device through RPC.
 """
+import logging
 import sys
 
 from .autotvm import module_loader
@@ -29,8 +30,18 @@
 
 __version__ = "0.1.0"
 
-# do not from tvm import topi when running vta.exec.rpc_server
-# to maintain minimum dependency on the board
-if sys.argv[0] not in ("-c", "-m"):
+_LOG = logging.getLogger(__name__)
+
+# do not from tvm import topi when __main__ is in vta_onboard
+# to maintain minimum Python dependencies on the board.
+# TODO(vta-team): move board-only logic imported above into vta_onboard.
+if "vta_onboard" not in sys.modules:
     from . import top
     from .build_module import build_config, lower, build
+else:
+    _LOG.warning(
+        "NOTE: some sub-packages of vta were not imported because the vta_onboard package "
+        "was detected in sys.modules. VTA assumes this indicates you are running on the "
+        "FPGA board. The full vta package requires dependencies that are too burdensome "
+        "to install in this environment."
+    )

vta/python/vta_onboard/__init__.py

@@ -0,0 +1,18 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+"""Defines a package that can be run onboard the FPGA's microcontroller."""

vta/python/vta/exec/rpc_server.py → vta/python/vta_onboard/exec/rpc_server.py

@@ -20,6 +20,10 @@
 """
 from __future__ import absolute_import
 
+# A marker used in vta.__init__ to detect whether to skip top-level imports to save time in starting
+# the RPC server. Must appear before importing vta package.
+VTA_SKIP_PACKAGE_IMPORTS = True
+
 import logging
 import argparse
 import os
@@ -30,8 +34,8 @@
 from tvm.contrib import cc
 from vta import program_bitstream
 
-from ..environment import get_env, pkg_config
-from ..libinfo import find_libvta
+from vta.environment import get_env, pkg_config
+from vta.libinfo import find_libvta
 
 
 def server_start():
@@ -124,7 +128,7 @@ def reconfig_runtime(cfg_json):
 
 
 def main():
-    """Main funciton"""
+    """Main function"""
     parser = argparse.ArgumentParser()
     parser.add_argument(
         "--host", type=str, default="0.0.0.0", help="The host IP address the server binds to"