added a simple register example

examples/README.md

@@ -10,6 +10,8 @@ included:
   packet, encapsulate it and send it to a special port.
 - `meter`: how to use indirect meters in P4.
 - `TLV_parsing`: how to parse IPv4 options
+- `register`: how to use registers in P4 and read / write the state from the
+  control plane
 
 All examples are orgranized the same way, with a `p4src` directory containing
 the P4 source code, and a `README` file describing the P4 program and explaining

examples/register/README.md

@@ -0,0 +1,20 @@
+# Register
+
+## Description
+
+This program illustrates as simply as possible how to use registers in P4 and
+read / write the register state using the bmv2 runtime CLI.
+
+This will probably change in the future but as of now the data plane is not
+doing anything (so don't try to send packets). However you can take a look at
+the P4 source code and at the read_register and write_register scripts. You can
+also run the following demo:
+
+### Running the demo
+
+To run the demo:
+- start the switch with `./run_switch.sh`.
+- write a register cell with `write_register.sh`. For example:
+  `./write_register.sh 123 88` to set `my_register[123]` to 88.
+- read a register cell with `read_register.sh`. For example:
+  `./read_register.sh 123` to read `my_register[123]`.

examples/register/p4src/register.p4

@@ -0,0 +1,87 @@
+/*
+Copyright 2013-present Barefoot Networks, Inc. 
+
+Licensed 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.
+*/
+
+header_type ethernet_t {
+    fields {
+        dstAddr : 48;
+        srcAddr : 48;
+        etherType : 16;
+    }
+}
+
+header_type intrinsic_metadata_t {
+    fields {
+        mcast_grp : 4;
+        egress_rid : 4;
+        mcast_hash : 16;
+        lf_field_list: 32;
+    }
+}
+
+header_type meta_t {
+    fields {
+        register_tmp : 32;
+    }
+}
+
+metadata meta_t meta;
+
+parser start {
+    return parse_ethernet;
+}
+
+header ethernet_t ethernet;
+metadata intrinsic_metadata_t intrinsic_metadata;
+
+parser parse_ethernet {
+    extract(ethernet);
+    return ingress;
+}
+
+action _drop() {
+    drop();
+}
+
+action _nop() {
+}
+
+register my_register {
+    width: 32;
+    static: m_table;
+    instance_count: 16384;
+}
+
+action m_action(register_idx) {
+    register_read(meta.register_tmp, my_register, register_idx);
+    // TODO
+}
+
+table m_table {
+    reads {
+        ethernet.srcAddr : exact;
+    }
+    actions {
+        m_action; _nop;
+    }
+    size : 16384;
+}
+
+control ingress {
+    apply(m_table);
+}
+
+control egress {
+}

examples/register/read_register.sh

@@ -0,0 +1,29 @@
+#!/bin/bash
+
+# Copyright 2013-present Barefoot Networks, Inc. 
+# 
+# Licensed 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.
+
+THIS_DIR=$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )
+
+source $THIS_DIR/../env.sh
+
+CLI_PATH=$BMV2_PATH/targets/simple_switch/sswitch_CLI
+
+if [ $# -lt 1 ]; then
+    echo "Please specify register index"
+    exit 1
+fi
+index=$1
+
+echo "register_read my_register $index" | $CLI_PATH register.json

examples/register/run_switch.sh

@@ -0,0 +1,37 @@
+#!/bin/bash
+
+# Copyright 2013-present Barefoot Networks, Inc. 
+# 
+# Licensed 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.
+
+THIS_DIR=$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )
+
+source $THIS_DIR/../env.sh
+
+P4C_BM_SCRIPT=$P4C_BM_PATH/p4c_bm/__main__.py
+
+SWITCH_PATH=$BMV2_PATH/targets/simple_switch/simple_switch
+
+CLI_PATH=$BMV2_PATH/targets/simple_switch/sswitch_CLI
+
+# Probably not very elegant but it works nice here: we enable interactive mode
+# to be able to use fg. We start the switch in the background, sleep for 2
+# minutes to give it time to start, then add the entries and put the switch
+# process back in the foreground
+set -m
+$P4C_BM_SCRIPT p4src/register.p4 --json register.json
+sudo echo "sudo" > /dev/null
+sudo $BMV2_PATH/targets/simple_switch/simple_switch register.json \
+    -i 0@veth0 -i 1@veth2 -i 2@veth4 -i 3@veth6 -i 4@veth8 \
+    --nanolog ipc:///tmp/bm-0-log.ipc \
+    --pcap

examples/register/write_register.sh

@@ -0,0 +1,30 @@
+#!/bin/bash
+
+# Copyright 2013-present Barefoot Networks, Inc. 
+# 
+# Licensed 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.
+
+THIS_DIR=$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )
+
+source $THIS_DIR/../env.sh
+
+CLI_PATH=$BMV2_PATH/targets/simple_switch/sswitch_CLI
+
+if [ $# -lt 2 ]; then
+    echo "Please specify register index and value, in this order"
+    exit 1
+fi
+index=$1
+value=$2
+
+echo "register_write my_register $index $value" | $CLI_PATH register.json