Chrysler: calculate checksum in can packer/parser (#255)

* calculate chrysler checksum in can packer/parser

* remove comment

can/common.cc

@@ -35,6 +35,38 @@ unsigned int subaru_checksum(unsigned int address, uint64_t d, int l) {
   return s & 0xFF;
 }
 
+unsigned int chrysler_checksum(unsigned int address, uint64_t d, int l) {
+  /* This function does not want the checksum byte in the input data.
+  jeep chrysler canbus checksum from http://illmatics.com/Remote%20Car%20Hacking.pdf */
+  uint8_t checksum = 0xFF;
+  for (int j = 0; j < (l - 1); j++) {
+    uint8_t shift = 0x80;
+    uint8_t curr = (d >> 8*j) & 0xFF;
+    for (int i=0; i<8; i++) {
+      uint8_t bit_sum = curr & shift;
+      uint8_t temp_chk = checksum & 0x80U;
+      if (bit_sum != 0U) {
+        bit_sum = 0x1C;
+        if (temp_chk != 0U) {
+          bit_sum = 1;
+        }
+        checksum = checksum << 1;
+        temp_chk = checksum | 1U;
+        bit_sum ^= temp_chk;
+      } else {
+        if (temp_chk != 0U) {
+          bit_sum = 0x1D;
+        }
+        checksum = checksum << 1;
+        bit_sum ^= checksum;
+      }
+      checksum = bit_sum;
+      shift = shift >> 1;
+    }
+  }
+  return ~checksum & 0xFF;
+}
+
 // Static lookup table for fast computation of CRC8 poly 0x2F, aka 8H2F/AUTOSAR
 uint8_t crc8_lut_8h2f[256];
 

can/common.h

@@ -14,6 +14,7 @@
 unsigned int honda_checksum(unsigned int address, uint64_t d, int l);
 unsigned int toyota_checksum(unsigned int address, uint64_t d, int l);
 unsigned int subaru_checksum(unsigned int address, uint64_t d, int l);
+unsigned int chrysler_checksum(unsigned int address, uint64_t d, int l);
 void init_crc_lookup_tables();
 unsigned int volkswagen_crc(unsigned int address, uint64_t d, int l);
 unsigned int pedal_checksum(uint64_t d, int l);

can/common.pxd

@@ -19,7 +19,8 @@ cdef extern from "common_dbc.h":
     PEDAL_COUNTER,
     VOLKSWAGEN_CHECKSUM,
     VOLKSWAGEN_COUNTER,
-    SUBARU_CHECKSUM
+    SUBARU_CHECKSUM,
+    CHRYSLER_CHECKSUM
 
   cdef struct Signal:
     const char* name

can/common_dbc.h

@@ -39,6 +39,7 @@ enum SignalType {
   VOLKSWAGEN_CHECKSUM,
   VOLKSWAGEN_COUNTER,
   SUBARU_CHECKSUM,
+  CHRYSLER_CHECKSUM,
 };
 
 struct Signal {

can/dbc_template.cc

@@ -31,6 +31,8 @@ const Signal sigs_{{address}}[] = {
       .type = SignalType::VOLKSWAGEN_COUNTER,
       {% elif checksum_type == "subaru" and sig.name == "CHECKSUM" %}
       .type = SignalType::SUBARU_CHECKSUM,
+      {% elif checksum_type == "chrysler" and sig.name == "CHECKSUM" %}
+      .type = SignalType::CHRYSLER_CHECKSUM,
       {% elif address in [512, 513] and sig.name == "CHECKSUM_PEDAL" %}
       .type = SignalType::PEDAL_CHECKSUM,
       {% elif address in [512, 513] and sig.name == "COUNTER_PEDAL" %}

can/packer.cc

@@ -102,6 +102,9 @@ uint64_t CANPacker::pack(uint32_t address, const std::vector<SignalPackValue> &s
     } else if (sig.type == SignalType::SUBARU_CHECKSUM) {
       unsigned int chksm = subaru_checksum(address, ret, message_lookup[address].size);
       ret = set_value(ret, sig, chksm);
+    } else if (sig.type == SignalType::CHRYSLER_CHECKSUM) {
+      unsigned int chksm = chrysler_checksum(address, ReverseBytes(ret), message_lookup[address].size);
+      ret = set_value(ret, sig, chksm);
     } else {
       //WARN("CHECKSUM signal type not valid\n");
     }

can/parser.cc

@@ -57,6 +57,11 @@ bool MessageState::parse(uint64_t sec, uint16_t ts_, uint8_t * dat) {
         if (!update_counter_generic(tmp, sig.b2)) {
         return false;
       }
+    } else if (sig.type == SignalType::CHRYSLER_CHECKSUM) {
+      if (chrysler_checksum(address, dat_le, size) != tmp) {
+        INFO("0x%X CHECKSUM FAIL\n", address);
+        return false;
+      }
     } else if (sig.type == SignalType::PEDAL_CHECKSUM) {
       if (pedal_checksum(dat_be, size) != tmp) {
         INFO("0x%X PEDAL CHECKSUM FAIL\n", address);

can/process_dbc.py

@@ -53,6 +53,13 @@ def process(in_fn, out_fn):
     checksum_start_bit = 0
     counter_start_bit = None
     little_endian = True
+  elif can_dbc.name.startswith(("chrysler_")):
+    checksum_type = "chrysler"
+    checksum_size = 8
+    counter_size = None
+    checksum_start_bit = 7
+    counter_start_bit = None
+    little_endian = False
   else:
     checksum_type = None
     checksum_size = None