diff --git a/src/cmd.cpp b/src/cmd.cpp
new file mode 100644
index 0000000..3a97498
--- /dev/null
+++ b/src/cmd.cpp
@@ -0,0 +1,99 @@
+#include "cmd.hpp"
+
+#include <fmt/format.h>
+
+#include <sdbusplus/bus.hpp>
+#include <sdbusplus/exception.hpp>
+#include <sdbusplus/message.hpp>
+#include <sdbusplus/slot.hpp>
+#include <stdplus/exception.hpp>
+#include <stdplus/fd/ops.hpp>
+#include <stdplus/types.hpp>
+
+#include <array>
+#include <map>
+#include <stdexcept>
+#include <tuple>
+#include <utility>
+#include <variant>
+#include <vector>
+
+namespace kcsbridge
+{
+
+using sdbusplus::bus::bus;
+using sdbusplus::message::message;
+using sdbusplus::slot::slot;
+
+void write(stdplus::Fd& kcs, message&& m)
+{
+    std::array<uint8_t, 1024> buffer;
+    stdplus::span<uint8_t> out(buffer.begin(), 3);
+    try
+    {
+        if (m.is_method_error())
+        {
+            // Extra copy to workaround lack of `const sd_bus_error` constructor
+            auto error = *m.get_error();
+            throw sdbusplus::exception::SdBusError(&error, "ipmid response");
+        }
+        std::tuple<uint8_t, uint8_t, uint8_t, uint8_t, std::vector<uint8_t>>
+            ret;
+        m.read(ret);
+        const auto& [netfn, lun, cmd, cc, data] = ret;
+        // Based on the IPMI KCS spec Figure 9-2
+        // netfn needs to be changed to odd in KCS responses
+        if (data.size() + 3 > buffer.size())
+        {
+            throw std::runtime_error(fmt::format(
+                "too large {} > {}", data.size() + 3, buffer.size()));
+        }
+        buffer[0] = (netfn | 1) << 2;
+        buffer[0] |= lun;
+        buffer[1] = cmd;
+        buffer[2] = cc;
+        memcpy(&buffer[3], data.data(), data.size());
+        out = stdplus::span<uint8_t>(buffer.begin(), data.size() + 3);
+    }
+    catch (const std::exception& e)
+    {
+        fmt::print(stderr, "IPMI response failure: {}\n", e.what());
+        buffer[0] |= 1 << 2;
+        buffer[2] = 0xff;
+    }
+    stdplus::fd::writeExact(kcs, out);
+}
+
+void read(stdplus::Fd& kcs, bus& bus, slot& outstanding)
+{
+    std::array<uint8_t, 1024> buffer;
+    auto in = stdplus::fd::read(kcs, buffer);
+    if (in.empty())
+    {
+        return;
+    }
+    if (outstanding)
+    {
+        fmt::print(stderr, "Canceling outstanding request\n");
+        outstanding = slot(nullptr);
+    }
+    if (in.size() < 2)
+    {
+        fmt::print(stderr, "Read too small, ignoring\n");
+        return;
+    }
+    auto m = bus.new_method_call("xyz.openbmc_project.Ipmi.Host",
+                                 "/xyz/openbmc_project/Ipmi",
+                                 "xyz.openbmc_project.Ipmi.Server", "execute");
+    std::map<std::string, std::variant<int>> options;
+    // Based on the IPMI KCS spec Figure 9-1
+    uint8_t netfn = in[0] >> 2, lun = in[0] & 3, cmd = in[1];
+    m.append(netfn, lun, cmd, in.subspan(2), options);
+    outstanding = m.call_async(
+        stdplus::exception::ignore([&outstanding, &kcs](message&& m) {
+            outstanding = slot(nullptr);
+            write(kcs, std::move(m));
+        }));
+}
+
+} // namespace kcsbridge