feat: implement cel_crsf_param_write

Fire-and-forget parameter write. Builds CRSF PARAM_WRITE frame
and sends it over the serial port.

celrs/crsf_param.c

@@ -27,13 +27,14 @@ int cel_crsf_param_read(cel_serial_port* port, uint8_t index,
 
 int cel_crsf_param_write(cel_serial_port* port, uint8_t index,
                           uint8_t value) {
-    /* TODO: send param write frame.
-     * Use cel_crsf_build_param_write_frame() + cel_serial_write().
-     * No response expected for write — fire and forget. */
-    (void)port;
-    (void)index;
-    (void)value;
-    return -1;
+    if (port == NULL) return -1;
+
+    uint8_t frame[16];
+    size_t len = cel_crsf_build_param_write_frame(frame, index, value);
+    if (len == 0) return -1;
+
+    size_t written = cel_serial_write(port, frame, len);
+    return (written == len) ? 0 : -1;
 }
 
 int cel_crsf_param_set_power(cel_serial_port* port, int mw,

tests/CMakeLists.txt

@@ -55,11 +55,12 @@ target_compile_features(test_crsf_telemetry PRIVATE c_std_23)
 add_test(NAME test_crsf_telemetry COMMAND test_crsf_telemetry)
 list(APPEND TEST_TARGETS test_crsf_telemetry)
 
-# CRSF param tests — pure functions (parse), no mock needed
+# CRSF param tests — mocks serial for write/ping/read
 add_executable(test_crsf_param test_crsf_param.c)
 target_include_directories(test_crsf_param PRIVATE "${CMAKE_SOURCE_DIR}")
-target_link_libraries(test_crsf_param PRIVATE celrs_crsf Unity::Unity)
+target_link_libraries(test_crsf_param PRIVATE celrs_crsf celrs_serial Unity::Unity CMock::CMock)
 target_compile_features(test_crsf_param PRIVATE c_std_23)
+cmock_generate_mock(test_crsf_param "${CMAKE_SOURCE_DIR}/celrs/platform/serial_internal.h")
 add_test(NAME test_crsf_param COMMAND test_crsf_param)
 list(APPEND TEST_TARGETS test_crsf_param)
 

tests/test_crsf_param.c

@@ -1,9 +1,16 @@
 #include "unity.h"
 #include "celrs/crsf_param.h"
+#include "Mockserial_internal.h"
 #include <string.h>
 
-void setUp(void) {}
-void tearDown(void) {}
+void setUp(void) {
+    Mockserial_internal_Init();
+}
+
+void tearDown(void) {
+    Mockserial_internal_Verify();
+    Mockserial_internal_Destroy();
+}
 
 /* cel_crsf_param_parse tests */
 
@@ -161,6 +168,38 @@ void test_param_parse_options_truncation(void) {
     TEST_ASSERT_EQUAL_UINT8(255, strlen(param.options)); /* truncated to 255 */
 }
 
+/* cel_crsf_param_write tests */
+
+void test_param_write_null_port(void) {
+    TEST_ASSERT_EQUAL_INT(-1, cel_crsf_param_write(NULL, 0, 0));
+}
+
+void test_param_write_success(void) {
+    cel_serial_platform_open_ExpectAndReturn("COM3", 400000,
+        (cel_serial_platform_handle)42);
+    cel_serial_port* port = cel_serial_open("COM3", 400000);
+    TEST_ASSERT_NOT_NULL(port);
+
+    cel_serial_platform_write_ExpectAnyArgsAndReturn(8);
+    TEST_ASSERT_EQUAL_INT(0, cel_crsf_param_write(port, 5, 3));
+
+    cel_serial_platform_close_Expect((cel_serial_platform_handle)42);
+    cel_serial_close(port);
+}
+
+void test_param_write_partial_write(void) {
+    cel_serial_platform_open_ExpectAndReturn("COM3", 400000,
+        (cel_serial_platform_handle)42);
+    cel_serial_port* port = cel_serial_open("COM3", 400000);
+    TEST_ASSERT_NOT_NULL(port);
+
+    cel_serial_platform_write_ExpectAnyArgsAndReturn(4);
+    TEST_ASSERT_EQUAL_INT(-1, cel_crsf_param_write(port, 5, 3));
+
+    cel_serial_platform_close_Expect((cel_serial_platform_handle)42);
+    cel_serial_close(port);
+}
+
 int main(void) {
     UNITY_BEGIN();
     RUN_TEST(test_param_parse_null_args);
@@ -172,5 +211,8 @@ int main(void) {
     RUN_TEST(test_param_parse_folder);
     RUN_TEST(test_param_parse_name_truncation);
     RUN_TEST(test_param_parse_options_truncation);
+    RUN_TEST(test_param_write_null_port);
+    RUN_TEST(test_param_write_success);
+    RUN_TEST(test_param_write_partial_write);
     return UNITY_END();
 }