Zero-copy ethernet TX: encode directly into prepend_buffer, add info/test skills

.claude/skills/info/SKILL.md

@@ -0,0 +1,7 @@
+---
+name: info
+description: Query device info from connected Picos. Use when the user says "info", "check devices", or wants to verify devices are responding.
+user-invocable: true
+---
+
+Run `go run ./cmd/picomap/ info` from the project root. This queries all connected devices and prints board ID, MAC, IP, and firmware name.

.claude/skills/test/SKILL.md

@@ -0,0 +1,10 @@
+---
+name: test
+description: Run device tests on connected Picos. Use when the user says "test", "run tests", or wants to verify firmware behavior.
+user-invocable: true
+---
+
+Run `go run ./cmd/picomap/ test all` from the project root. This runs all registered tests on the test device.
+
+To list available tests: `go run ./cmd/picomap/ test list`
+To run a specific test: `go run ./cmd/picomap/ test run <name>`

firmware/include/dispatch.h

@@ -6,17 +6,17 @@
 #include <span>
 #include "wire.h"
 #include "timer_queue.h"
+#include "net.h"
 
 struct responder {
     uint32_t message_id;
-    std::function<void(std::span<const uint8_t>)> send;
+    send_fn send;
 
     template <typename T>
     void respond(const T& msg) const {
-        uint8_t buf[1024];
+        send([&](span_writer& out) {
-        span_writer out(buf, sizeof(buf));
+            return encode_response_into(out, message_id, msg);
-        auto r = encode_response_into(out, message_id, msg);
+        });
-        if (r) send({buf, *r});
     }
 };
 

firmware/include/net.h

@@ -13,8 +13,11 @@ struct net_state {
     ipv4::ip4_addr ip;
 };
 
+using encode_fn = std::function<msgpack::result<size_t>(span_writer&)>;
+using send_fn = std::function<void(encode_fn)>;
+
 using net_handler = std::function<void(std::span<const uint8_t> payload,
-                                       std::function<void(std::span<const uint8_t>)> send)>;
+                                       send_fn send)>;
 
 using net_frame_callback = std::function<bool(std::span<const uint8_t> frame)>;
 

firmware/lib/dispatch.cpp

@@ -45,7 +45,7 @@ bool dispatch_cancel_timer(timer_handle h) {
     static static_vector<uint8_t, 4096> usb_rx_buf;
     static std::array<uint8_t, 4096> tx_buf;
 
-    auto dispatch_msg = [&](const DecodedMessage& msg, std::function<void(std::span<const uint8_t>)> send) {
+    auto dispatch_msg = [&](const DecodedMessage& msg, send_fn send) {
         auto it = handler_map.find(msg.type_id);
         if (it == handler_map.end()) {
             dlogf("dispatch: unknown type_id %d", msg.type_id);
@@ -56,7 +56,7 @@ bool dispatch_cancel_timer(timer_handle h) {
     };
 
     net_set_handler([&](std::span<const uint8_t> payload,
-                        std::function<void(std::span<const uint8_t>)> send) {
+                        send_fn send) {
         auto msg = try_decode(payload.data(), payload.size());
         if (!msg) return;
         dispatch_msg(*msg, std::move(send));
@@ -82,7 +82,12 @@ bool dispatch_cancel_timer(timer_handle h) {
                 continue;
             }
 
-            dispatch_msg(*msg, [&](std::span<const uint8_t> data) {
+            dispatch_msg(*msg, [&](encode_fn encode) {
+                uint8_t buf[4096];
+                span_writer out(buf, sizeof(buf));
+                auto r = encode(out);
+                if (!r) return;
+                std::span<const uint8_t> data{buf, *r};
                 if (data.size() <= usb.tx.free()) {
                     if (!usb.send(data))
                         dlogf("usb send failed: %zu bytes, %u free", data.size(), usb.tx.free());

firmware/lib/net.cpp

@@ -52,11 +52,14 @@ static void handle_udp(std::span<const uint8_t> frame, span_writer& tx) {
     uint16_t dst_port = uhdr->src_port;
 
     msg_handler(pb.remaining().subspan(0, payload_len),
-        [dst_mac, dst_ip, dst_port](std::span<const uint8_t> resp_data) {
+        [dst_mac, dst_ip, dst_port](encode_fn encode) {
             prepend_buffer<4096> buf;
-            buf.append_copy(resp_data);
+            span_writer out(buf.payload_ptr(), 2048);
+            auto r = encode(out);
+            if (!r) return;
+            buf.append(*r);
             udp::prepend(buf, dst_mac, state.mac, state.ip, dst_ip,
-                         PICOMAP_PORT, dst_port, resp_data.size());
+                         PICOMAP_PORT, dst_port, *r);
             net_send_raw(buf.span());
         });
 }