board/sg-cmd.c: Add "sg" req/resp packets

board/sg-cmd.h

@@ -0,0 +1,43 @@
+#pragma once
+
+#include <windows.h>
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include "hook/iobuf.h"
+
+struct sg_header {
+    uint8_t frame_len;
+    uint8_t addr;
+    uint8_t seq_no;
+    uint8_t cmd;
+};
+
+struct sg_req_header {
+    struct sg_header hdr;
+    uint8_t payload_len;
+};
+
+struct sg_resp_header {
+    struct sg_header hdr;
+    uint8_t status;
+    uint8_t payload_len;
+};
+
+typedef HRESULT (*sg_dispatch_fn_t)(
+        void *ctx,
+        const void *req,
+        void *resp);
+
+void sg_req_transact(
+        struct iobuf *resp_frame,
+        const uint8_t *req_bytes,
+        size_t req_nbytes,
+        sg_dispatch_fn_t dispatch,
+        void *ctx);
+
+void sg_resp_init(
+        struct sg_resp_header *resp,
+        const struct sg_req_header *req,
+        size_t payload_len);