driver/slipmux: Implement fcs for config frames

Author: Teufelchen1

drivers/slipdev/include/slipdev_internal.h

@@ -55,6 +55,39 @@ extern "C" {
 #define SLIPDEV_CONFIG_START (0xa9U)
 /** @} */
 
+
+/* Special init
+ * the result of normal fcs init combined with slipmux config start (0xa9)
+ */
+#define SPECIAL_INIT_FCS (0x374cU)
+#define INIT_FCS (0xffffU)
+#define GOOD_FCS (0xf0b8U)
+
+static const uint16_t FCS_LOOKUP[256] = {
+    0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf, 0x8c48, 0x9dc1, 0xaf5a, 0xbed3,
+    0xca6c, 0xdbe5, 0xe97e, 0xf8f7, 0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e,
+    0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876, 0x2102, 0x308b, 0x0210, 0x1399,
+    0x6726, 0x76af, 0x4434, 0x55bd, 0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5,
+    0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c, 0xbdcb, 0xac42, 0x9ed9, 0x8f50,
+    0xfbef, 0xea66, 0xd8fd, 0xc974, 0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb,
+    0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3, 0x5285, 0x430c, 0x7197, 0x601e,
+    0x14a1, 0x0528, 0x37b3, 0x263a, 0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72,
+    0x6306, 0x728f, 0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9, 0xef4e, 0xfec7, 0xcc5c, 0xddd5,
+    0xa96a, 0xb8e3, 0x8a78, 0x9bf1, 0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738,
+    0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862, 0x9af9, 0x8b70, 0x8408, 0x9581, 0xa71a, 0xb693,
+    0xc22c, 0xd3a5, 0xe13e, 0xf0b7, 0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff,
+    0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036, 0x18c1, 0x0948, 0x3bd3, 0x2a5a,
+    0x5ee5, 0x4f6c, 0x7df7, 0x6c7e, 0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5,
+    0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd, 0xb58b, 0xa402, 0x9699, 0x8710,
+    0xf3af, 0xe226, 0xd0bd, 0xc134, 0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c,
+    0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a, 0xb2b3, 0x4a44, 0x5bcd, 0x6956, 0x78df,
+    0x0c60, 0x1de9, 0x2f72, 0x3efb, 0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232,
+    0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a, 0xe70e, 0xf687, 0xc41c, 0xd595,
+    0xa12a, 0xb0a3, 0x8238, 0x93b1, 0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9,
+    0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330, 0x7bc7, 0x6a4e, 0x58d5, 0x495c,
+    0x3de3, 0x2c6a, 0x1ef1, 0x0f78
+};
+
 /**
  * @brief   ISR pipe to hand read bytes to stdin
  */

drivers/slipdev/slipdev.c

@@ -408,33 +408,63 @@ static const netdev_driver_t slip_driver = {
 };
 
 #if IS_USED(MODULE_SLIPDEV_STDIO)
+static uint16_t _fcs_part(const uint8_t * data, size_t len) {
+    uint16_t fcs = SPECIAL_INIT_FCS;
+    for (size_t i = 0; i < len; ++i)
+    {
+        fcs = (fcs >> 8) ^ FCS_LOOKUP[(fcs ^ data[i]) & 0xff];
+    }
+    return fcs;
+}
+
+static int check_fcs(const uint8_t * data, size_t len) {
+    uint16_t trialfcs = _fcs_part(data, len);
+    return trialfcs == GOOD_FCS;
+}
+
+static uint16_t fcs(const uint8_t * data, size_t len) {
+    uint16_t trialfcs = _fcs_part(data, len);
+    uint16_t result = trialfcs ^ INIT_FCS;
+    return result;
+}
+
 static void *_coap_server_thread(void *arg)
 {
     static uint8_t buf[512];
     slipdev_t *dev = arg;
-    DEBUG("Started coap_server thread\n");
     while (1) {
         thread_flags_wait_any(1);
         size_t len;
         while (crb_get_chunk_size(&dev->rb_config, &len)) {
             crb_consume_chunk(&dev->rb_config, buf, len);
 
+            if (!check_fcs(buf, len)) {
+                break;
+            }
+
+            // cut off the FCS checksum at the end
+            size_t pktlen = len - 2;
+
             coap_pkt_t pkt;
             sock_udp_ep_t remote;
             coap_request_ctx_t ctx = {
                 .remote = &remote,
             };
-            if (coap_parse(&pkt, (uint8_t *)buf, len) < 0) {
+            if (coap_parse(&pkt, buf, pktlen) < 0) {
                 break;
             }
             unsigned int res = 0;
-            if ((res = coap_handle_req(&pkt, (uint8_t *) buf, 512, &ctx)) <= 0) {
+            if ((res = coap_handle_req(&pkt, buf, sizeof(buf), &ctx)) <= 0) {
                 break;
             }
 
+            uint16_t fcs_sum = fcs(buf, res);
+
             slipdev_lock();
             slipdev_write_byte(dev->config.uart, SLIPDEV_CONFIG_START);
             slipdev_write_bytes(dev->config.uart, buf, res);
+            slipdev_write_byte(dev->config.uart, fcs_sum);
+            slipdev_write_byte(dev->config.uart, fcs_sum >> 8);
             slipdev_write_byte(dev->config.uart, SLIPDEV_END);
             slipdev_unlock();
         }

drivers/slipdev/stdio.c

@@ -34,9 +34,11 @@ static void _isrpipe_write(void *arg, uint8_t data)
 static void _init(void)
 {
     /* intentionally overwritten in netdev init so we have stdio before
-     * the network device is initialized is initialized */
+     * the network device is initialized */
     uart_init(slipdev_params[0].uart, slipdev_params[0].baudrate,
               _isrpipe_write, &stdin_isrpipe);
+    
+    slipdev_write_byte(slipdev_params[0].uart, SLIPDEV_END);
 }
 
 static ssize_t _write(const void *buffer, size_t len)