Add CRC-16 calculator for a firmware image

2026-08-30 14:52:51 +08:00 · 2025-10-20 07:29:39 +02:00
parent ac4f0d410f
commit 8499e9e464
2 changed files with 183 additions and 1 deletions
@@ -0,0 +1,179 @@
+/*
+ * Calculator for the CRC16 as described in AN27 by Dallas Semiconductor
+ * http://www.microshadow.com/files/files8051/app27.pdf
+ * The implementation in C is based on the code given in
+ * https://carta.tech/man-pages/man3/_crc_ibutton_update.3avr.html
+ * The polynomial of the CRC is 0xa001: x^16 + x^15 + x^2 + 1
+ */
+
+#include <stdio.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <argp.h>
+#include <string.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+
+// Use a 4MB buffer, the same as the flash rom size
+#define BUFFER_SIZE 0x400000
+char buffer[BUFFER_SIZE];
+
+struct arguments {
+	char *input_file;
+	char *output_file;
+	bool update;
+	bool verify;
+};
+
+const char *argp_program_version = "crc_calculator 0.1";
+const char *argp_program_bug_address = "https://github.com/logicog/RTLPlayground/issues";
+static char doc[] = "Calculate (and optionally update) the CRC of an image";
+static char args_doc[] = "crc_calculator [options] INPUT_IMAGE";
+static struct argp_option options[] = {
+    { "output", 'o', "FILE", 0, "Output image file name instead of overwriting input image"},
+    { "update", 'u', 0, OPTION_ARG_OPTIONAL, "Update the image with the CRC"},
+    { "verify", 'v', 0, OPTION_ARG_OPTIONAL, "Verify the CRC of the file"},
+    { 0 }
+};
+
+
+uint16_t crc16_update(uint16_t crc, uint8_t a)
+{
+    crc ^= a;
+    for (int i = 0; i < 8; ++i)
+	    crc = crc & 1 ? (crc >> 1) ^ 0xA001 : crc >> 1;
+
+    return crc;
+}
+
+
+static error_t parse_opt(int key, char *arg, struct argp_state *state)
+{
+	struct arguments *arguments = state->input;
+	switch (key) {
+	case 'u':
+		arguments->update = true;
+		break;
+	case 'v':
+		arguments->verify = true;
+		break;
+	case 'o':
+		arguments->output_file = arg;
+		break;
+	default:
+		return ARGP_ERR_UNKNOWN;
+    }
+    return 0;
+}
+
+
+static struct argp argp = {
+	options, parse_opt, args_doc, doc, 0, 0, 0
+};
+
+
+int main(int argc, char **argv)
+{
+	struct arguments arguments;
+	int arg_index;
+	char tmpfilename[] = "crc_XXXXXX";
+	uint16_t crc = 0;
+	FILE *inptr;
+	int outptr;
+	int range;
+
+	arguments.input_file = NULL;
+	arguments.output_file = NULL;
+	arguments.update = false;
+	arguments.verify = false;
+
+	argp_parse(&argp, argc, argv, 0, &arg_index, &arguments);
+	if (!arg_index)
+		argp_usage (0);
+
+	memset(buffer, 0, BUFFER_SIZE);
+
+	size_t filesize = 0;
+	if (argv[arg_index]) {
+		inptr = fopen(argv[arg_index], "rb");
+		if (inptr == NULL) {
+			printf("Cannot open input file %s\n", argv[arg_index]);
+			return 5;
+		}
+
+		fseek(inptr, 0L, SEEK_END);
+		filesize = ftell(inptr);
+		rewind(inptr);
+		printf("Input file size: %ld\n", filesize);
+		if (filesize > BUFFER_SIZE) {
+			printf("File too large.\n");
+			return 5;
+		}
+		size_t bytes_read = fread(buffer, 1, sizeof(buffer), inptr);
+
+		printf("Bytes read: %ld\n", bytes_read);
+
+		if (bytes_read != filesize) {
+			printf("Error reading input file.\n");
+			return 5;
+		}
+		fclose(inptr);
+	}
+
+	range = filesize;
+	if (!arguments.verify) {
+		if (arguments.update) {
+			range -= 2;
+		} else if (arguments.output_file) {
+			filesize += 2;
+		}
+	}
+
+	for (int i = 0; i < range; i++)
+		crc = crc16_update(crc, buffer[i]);
+
+	printf("CRC16 is: 0x%04x\n", crc);
+
+	if (arguments.verify) {
+		if (crc == 0xb001) {
+			printf("Checksum OK\n");
+			return 0;
+		} else {
+			printf("Checksum Incorrect\n");
+			return 5;
+		}
+	}
+
+	// We have to create a new image with updated CRC
+	if (arguments.update || arguments.output_file) {
+		crc ^= 0xffff;
+		printf("Setting CRC bytes at position: 0x%x to CRC 1s complement 0x%04x\n", range, crc);
+		// The CRC algorithm expects as input always first the LO-Byte
+		buffer[range] = crc;
+		buffer[range + 1] = crc >> 8;
+
+		if (!arguments.update)
+			outptr = creat(arguments.output_file, S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP);
+		else
+			outptr = mkstemp(tmpfilename);
+
+		if (!outptr) {
+			printf("Cannot open %s\n", arguments.output_file);
+			return 5;
+		}
+		size_t written = write(outptr, buffer, filesize);
+
+		if (written != filesize) {
+			printf("Error writing output file.\n");
+			return 5;
+		}
+		close(outptr);
+
+		if (arguments.update)
+			rename(tmpfilename, argv[arg_index]);
+	}
+
+	return 0;
+}