Implemented disabling of GDB packet acknowledgement, and disabled it by default. The new packetAcknowledgement debug server config param can be used to keep it enabled.

src/DebugServer/Gdb/AvrGdb/AvrGdbRsp.cpp

@@ -155,11 +155,18 @@ namespace DebugServer::Gdb::AvrGdb
     }
 
     std::set<std::pair<Feature, std::optional<std::string>>> AvrGdbRsp::getSupportedFeatures() {
-        return {
+        auto output = std::set<std::pair<Feature, std::optional<std::string>>>{
+            {Feature::HARDWARE_BREAKPOINTS, std::nullopt},
             {Feature::SOFTWARE_BREAKPOINTS, std::nullopt},
             {Feature::MEMORY_MAP_READ, std::nullopt},
             {Feature::VCONT_ACTIONS_QUERY, std::nullopt},
         };
+
+        if (!this->debugServerConfig.packetAcknowledgement) {
+            output.emplace(Feature::NO_ACK_MODE, std::nullopt);
+        }
+
+        return output;
     }
 
     void AvrGdbRsp::handleTargetStoppedGdbResponse(Targets::TargetMemoryAddress programAddress) {

src/DebugServer/Gdb/CommandPackets/CommandPacket.cpp

@@ -61,6 +61,17 @@ namespace DebugServer::Gdb::CommandPackets
             return;
         }
 
+        if (!debugSession.serverConfig.packetAcknowledgement && packetString.find("QStartNoAckMode") == 0) {
+            Logger::info("Handling QStartNoAckMode");
+            /*
+             * We respond to the command before actually disabling packet acknowledgement, because GDB will send one
+             * final acknowledgement byte to acknowledge the response.
+             */
+            debugSession.connection.writePacket(OkResponsePacket{});
+            debugSession.connection.packetAcknowledgement = false;
+            return;
+        }
+
         Logger::debug("Unknown GDB RSP packet: " + packetString + " - returning empty response");
 
         // GDB expects an empty response for all unsupported commands

src/DebugServer/Gdb/Connection.cpp

@@ -135,8 +135,10 @@ namespace DebugServer::Gdb
                             )
                     );
 
-                    // Acknowledge receipt
-                    this->write({'+'});
+                    if (this->packetAcknowledgement) {
+                        // Acknowledge receipt
+                        this->write({'+'});
+                    }
 
                     output.emplace_back(std::move(rawPacket));
                     byteIndex = packetIndex;
@@ -149,22 +151,32 @@ namespace DebugServer::Gdb
     }
 
     void Connection::writePacket(const ResponsePacket& packet) {
-        // Write the packet repeatedly until the GDB client acknowledges it.
-        int attempts = 0;
         const auto rawPacket = packet.toRawPacket();
 
         Logger::debug("Writing GDB packet: " + std::string{rawPacket.begin(), rawPacket.end()});
 
-        do {
-            if (attempts > 10) {
-                throw ClientCommunicationError{
-                    "Failed to write GDB response packet - client failed to acknowledge receipt - retry limit reached"
-                };
-            }
+        this->write(rawPacket);
 
-            this->write(rawPacket);
-            attempts++;
-        } while (this->readSingleByte(false).value_or(0) != '+');
+        if (this->packetAcknowledgement) {
+            auto attempts = std::size_t{0};
+            auto ackByte = this->readSingleByte(false);
+            while (ackByte != '+') {
+                if (attempts > 10) {
+                    throw ClientCommunicationError{
+                        "Failed to write GDB response packet - client failed to acknowledge receipt - retry limit reached"
+                    };
+                }
+
+                if (ackByte == '-') {
+                    // GDB has requested retransmission
+                    Logger::debug("Sending packet again, upon GDB's request");
+                    this->write(rawPacket);
+                }
+
+                ackByte = this->readSingleByte(false);
+                ++attempts;
+            }
+        }
     }
 
     void Connection::accept(int serverSocketFileDescriptor) {

src/DebugServer/Gdb/Connection.hpp

@@ -31,6 +31,8 @@ namespace DebugServer::Gdb
          */
         static constexpr auto ABSOLUTE_MAXIMUM_PACKET_READ_SIZE = 2097000; // 2MiB
 
+        bool packetAcknowledgement = true;
+
         Connection(int serverSocketFileDescriptor, EventFdNotifier& interruptEventNotifier);
 
         Connection() = delete;

src/DebugServer/Gdb/Feature.hpp

@@ -11,6 +11,7 @@ namespace DebugServer::Gdb
         PACKET_SIZE,
         MEMORY_MAP_READ,
         VCONT_ACTIONS_QUERY,
+        NO_ACK_MODE,
     };
 
     static inline BiMap<Feature, std::string> getGdbFeatureToNameMapping() {
@@ -20,6 +21,7 @@ namespace DebugServer::Gdb
             {Feature::PACKET_SIZE, "PacketSize"},
             {Feature::MEMORY_MAP_READ, "qXfer:memory-map:read"},
             {Feature::VCONT_ACTIONS_QUERY, "vContSupported"},
+            {Feature::NO_ACK_MODE, "QStartNoAckMode"},
         };
     }
 }

src/DebugServer/Gdb/GdbDebugServerConfig.cpp

@@ -42,5 +42,17 @@ namespace DebugServer::Gdb
                 );
             }
         }
+
+        if (debugServerConfig.debugServerNode["packetAcknowledgement"]) {
+            if (YamlUtilities::isCastable<bool>(debugServerConfig.debugServerNode["packetAcknowledgement"])) {
+                this->packetAcknowledgement = debugServerConfig.debugServerNode["packetAcknowledgement"].as<bool>();
+
+            } else {
+                Logger::error(
+                    "Invalid GDB debug server config parameter ('packetAcknowledgement') provided - value must be"
+                        " castable to a boolean. The parameter will be ignored."
+                );
+            }
+        }
     }
 }

src/DebugServer/Gdb/GdbDebugServerConfig.hpp

@@ -35,6 +35,19 @@ namespace DebugServer::Gdb
          */
         bool rangeStepping = true;
 
+        /**
+         * Determines whether Bloom will seek to disable packet acknowledgement with GDB, at the start of the debug
+         * session.
+         *
+         * If this is set to false, Bloom will communicate its ability to disable package acknowledgment to GDB.
+         * GDB may then send the appropriate packet to disable packet acknowledgment. However, this isn't
+         * guaranteed - GDB may be configured to keep packet acknowledgment enabled (via the
+         * `set remote noack-packet off` command).
+         *
+         * This parameter is optional. If not specified, the default value set here will be used.
+         */
+        bool packetAcknowledgement = false;
+
         explicit GdbDebugServerConfig(const DebugServerConfig& debugServerConfig);
     };
 }