From 79d84b226152f609197437cc2377b7bad540f4e7 Mon Sep 17 00:00:00 2001
From: Fredrik Thulin <fredrik@thulin.net>
Date: Thu, 23 Mar 2017 19:44:26 +0100
Subject: Add CRC32.

---
 slip.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

(limited to 'slip.c')

diff --git a/slip.c b/slip.c
index b28b7e1..279b1d3 100644
--- a/slip.c
+++ b/slip.c
@@ -73,15 +73,34 @@ hal_error_t hal_slip_send_char(const uint8_t c)
     return HAL_OK;
 }
 
+static hal_error_t _send_uint32(const uint32_t val)
+{
+    uint32_t data = val;
+
+    for (int i = 0; i < 4; ++i) {
+	uint8_t *p = (uint8_t *) &data;
+	check(hal_slip_send_char(p[i]));
+    }
+
+    return HAL_OK;
+}
+
 /* Send a message with SLIP framing.
  */
 hal_error_t hal_slip_send(const uint8_t * const buf, const size_t len)
 {
+    hal_crc32_t crc;
+
     /* send an initial END character to flush out any data that may
      * have accumulated in the receiver due to line noise
      */
     check(hal_serial_send_char(END));
 
+    /* Calculate CRC32 checksum of the contents, before SLIP encoding */
+    crc = hal_crc32_init();
+    crc = hal_crc32_update(crc, buf, len);
+    crc = ~hal_crc32_finalize(crc);
+
     /* for each byte in the packet, send the appropriate character
      * sequence
      */
@@ -91,6 +110,9 @@ hal_error_t hal_slip_send(const uint8_t * const buf, const size_t len)
             return ret;
     }
 
+    /* Transmit the CRC */
+    check(_send_uint32(crc));
+
     /* tell the receiver that we're done sending the packet
      */
     check(hal_serial_send_char(END));
-- 
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