modem: cmux: Define macros for header size

Define CMUX_HEADER_SIZE macro that is 6 or 7 bytes depending on
MTU.
Remove the previous CMUX_FRAME_SIZE_MAX that was a bit missleading
as it meant only the header size without a data and was fixed to 7 bytes.
Redefine new macros CMUX_FRAME_SIZE_MAX and CMUX_FRAME_SIZE_MIN which
are actually frame sizes with data included.

Signed-off-by: Seppo Takalo <[email protected]>

Author: SeppoTakalo

include/zephyr/modem/cmux.h

@@ -57,8 +57,15 @@ typedef void (*modem_cmux_callback)(struct modem_cmux *cmux, enum modem_cmux_eve
  * @cond INTERNAL_HIDDEN
  */
 
+#if CONFIG_MODEM_CMUX_MTU > 127
+#define MODEM_CMUX_HEADER_SIZE			7
+#else
+#define MODEM_CMUX_HEADER_SIZE			6
+#endif
+
+
 /* Total size of the CMUX work buffers */
-#define MODEM_CMUX_WORK_BUFFER_SIZE (CONFIG_MODEM_CMUX_MTU + 7 + \
+#define MODEM_CMUX_WORK_BUFFER_SIZE (CONFIG_MODEM_CMUX_MTU + MODEM_CMUX_HEADER_SIZE + \
 				     CONFIG_MODEM_CMUX_WORK_BUFFER_SIZE_EXTRA)
 
 enum modem_cmux_state {

subsys/modem/modem_cmux.c

@@ -21,14 +21,23 @@ LOG_MODULE_REGISTER(modem_cmux, CONFIG_MODEM_CMUX_LOG_LEVEL);
 #define MODEM_CMUX_EA				(0x01)
 #define MODEM_CMUX_CR				(0x02)
 #define MODEM_CMUX_PF				(0x10)
-#define MODEM_CMUX_FRAME_SIZE_MAX		(0x07)
-#define MODEM_CMUX_DATA_SIZE_MIN		(0x08)
-#define MODEM_CMUX_DATA_FRAME_SIZE_MIN		(MODEM_CMUX_FRAME_SIZE_MAX + \
-						 MODEM_CMUX_DATA_SIZE_MIN)
+#if CONFIG_MODEM_CMUX_MTU > 127
+#define MODEM_CMUX_HEADER_SIZE			7
+#else
+#define MODEM_CMUX_HEADER_SIZE			6
+#endif
+#define MODEM_CMUX_DATA_SIZE_MIN		8
+#define MODEM_CMUX_DATA_FRAME_SIZE_MIN          (MODEM_CMUX_HEADER_SIZE + MODEM_CMUX_DATA_SIZE_MIN)
+#define MODEM_CMUX_DATA_FRAME_SIZE_MAX		(MODEM_CMUX_HEADER_SIZE + CONFIG_MODEM_CMUX_MTU)
 
-#define MODEM_CMUX_CMD_DATA_SIZE_MAX		(0x08)
-#define MODEM_CMUX_CMD_FRAME_SIZE_MAX		(MODEM_CMUX_FRAME_SIZE_MAX + \
-						 MODEM_CMUX_CMD_DATA_SIZE_MAX)
+/* Biggest supported Multiplexer control commands in UIH frame
+ * Modem Status Command (MSC) - 5 bytes when Break is included.
+ *
+ * PN would be 10 bytes, but that is not implemented
+ */
+#define MODEM_CMUX_CMD_DATA_SIZE_MAX		5
+#define MODEM_CMUX_CMD_FRAME_SIZE_MAX           (MODEM_CMUX_HEADER_SIZE +  \
+						MODEM_CMUX_CMD_DATA_SIZE_MAX)
 
 #define MODEM_CMUX_T1_TIMEOUT			(K_MSEC(330))
 #define MODEM_CMUX_T2_TIMEOUT			(K_MSEC(660))
@@ -274,13 +283,13 @@ static void modem_cmux_bus_callback(struct modem_pipe *pipe, enum modem_pipe_eve
 static uint16_t modem_cmux_transmit_frame(struct modem_cmux *cmux,
 					  const struct modem_cmux_frame *frame)
 {
-	uint8_t buf[MODEM_CMUX_FRAME_SIZE_MAX];
+	uint8_t buf[MODEM_CMUX_HEADER_SIZE];
 	uint8_t fcs;
 	uint16_t space;
 	uint16_t data_len;
 	uint16_t buf_idx;
 
-	space = ring_buf_space_get(&cmux->transmit_rb) - MODEM_CMUX_FRAME_SIZE_MAX;
+	space = ring_buf_space_get(&cmux->transmit_rb) - MODEM_CMUX_HEADER_SIZE;
 	data_len = MIN(space, frame->data_len);
 	data_len = MIN(data_len, CONFIG_MODEM_CMUX_MTU);
 
@@ -1330,11 +1339,9 @@ void modem_cmux_init(struct modem_cmux *cmux, const struct modem_cmux_config *co
 	__ASSERT_NO_MSG(cmux != NULL);
 	__ASSERT_NO_MSG(config != NULL);
 	__ASSERT_NO_MSG(config->receive_buf != NULL);
-	__ASSERT_NO_MSG(config->receive_buf_size >=
-			(CONFIG_MODEM_CMUX_MTU + MODEM_CMUX_FRAME_SIZE_MAX));
+	__ASSERT_NO_MSG(config->receive_buf_size >= MODEM_CMUX_DATA_FRAME_SIZE_MAX);
 	__ASSERT_NO_MSG(config->transmit_buf != NULL);
-	__ASSERT_NO_MSG(config->transmit_buf_size >=
-			(CONFIG_MODEM_CMUX_MTU + MODEM_CMUX_FRAME_SIZE_MAX));
+	__ASSERT_NO_MSG(config->transmit_buf_size >= MODEM_CMUX_DATA_FRAME_SIZE_MAX);
 
 	memset(cmux, 0x00, sizeof(*cmux));
 	cmux->callback = config->callback;