Import of the watch repository from Pebble

src/fw/util/ihex.c

@@ -0,0 +1,52 @@
+/*
+ * Copyright 2024 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "util/ihex.h"
+
+typedef struct IHEXRecord {
+  char start;
+  char data_count[2];
+  char address[4];
+  char type[2];
+  char data[];  // Variable data and checksum
+} IHEXRecord;
+
+static void prv_hexlify(char *str, uint32_t value, uint8_t num_bytes) {
+  for (int i = num_bytes * 2 - 1; i >= 0; --i) {
+    uint8_t nibble = (value >> (4 * i)) & 0xF;
+    if (nibble >= 0xA) {
+      *str++ = 'A' + (nibble - 0xA);
+    } else {
+      *str++ = '0' + nibble;
+    }
+  }
+}
+
+void ihex_encode(uint8_t *out, uint8_t type, uint16_t address,
+                 const void *data, uint8_t data_len) {
+  IHEXRecord *record = (IHEXRecord *)out;
+  uint8_t checksum = data_len + (address >> 8) + (address & 0xff) + type;
+  record->start = ':';
+  prv_hexlify(record->data_count, data_len, sizeof(data_len));
+  prv_hexlify(record->address, address, sizeof(address));
+  prv_hexlify(record->type, type, sizeof(type));
+  for (uint16_t i = 0; i < data_len; ++i) {
+    uint8_t data_byte = ((uint8_t *)data)[i];
+    checksum += data_byte;
+    prv_hexlify(&record->data[i*2], data_byte, sizeof(data_byte));
+  }
+  prv_hexlify(&record->data[data_len*2], ~checksum + 1, sizeof(checksum));
+}