Added additional details for flags used in Lab3

Author: Bharathgopal

Lab3/README.MD

@@ -21,4 +21,57 @@ make run
 * To see Renode GUI terminal for logs and output: 
 ```
 renode renode/stm32.resc
-```
+```
+
+---
+
+# STM32 Build & Coverage Configuration Report
+This document outlines the flags and tools used to compile, simulate, and audit the `Lab3.elf` project.
+
+## 1. Compiler Flags (CFLAGS)
+The `CFLAGS` define how the C source code is translated into machine instructions for the target microcontroller.
+
+| Flag | Category | Description |
+| :--- | :--- | :--- |
+| `-mcpu=cortex-m4` | **Architecture** | Target the ARM Cortex-M4 processor and its specific instruction set. |
+| `-mthumb` | **Architecture** | Use the Thumb-2 instruction set (required for Cortex-M). |
+| `-O0` | **Optimization** | Disable optimizations. Ensures assembly matches C source 1-to-1 for accurate debugging and coverage. |
+| `-g` | **Debugging** | Include debug symbols for mapping memory addresses back to source code lines. |
+| `-ffreestanding` | **Environment** | Standard libraries may not be available; assumes no OS environment. |
+| `-fno-builtin` | **Environment** | Prevents compiler from replacing your functions with internal optimized versions. |
+| `-I<dir>` | **Search Path** | Adds `./src`, `./unity`, and `./stm32f4` to the header include search path. |
+| `-Wall -Wextra` | **Quality** | Enables almost all compiler warnings to catch potential bugs early. |
+
+---
+
+## 2. Linker Flags (LDFLAGS)
+The `LDFLAGS` define how object files are joined and where they are placed in the chip's memory.
+
+| Flag | Description |
+| :--- | :--- |
+| `-T stm32f4/linker.ld` | Uses the Linker Script to define the memory map (Flash vs. RAM boundaries). |
+| `-nostartfiles` | Excludes standard C startup files; uses the project's custom `startup.c` instead. |
+| `-Wl,--gc-sections` | Tells the linker to "Garbage Collect" (remove) unused functions to save Flash space. |
+
+---
+
+## 3. Automated Coverage Reporting
+To view coverage results both in the terminal and on the GitHub Actions summary page, the following `Makefile` target is used.
+
+### Makefile Target
+```makefile
+coverage:
+	@# Run the Renode tracer reader and pipe output to AWK
+	@python3 /opt/renode/tools/execution_tracer/execution_tracer_reader.py \
+		coverage ./coverage/trace.bin \
+		--binary Lab3.elf \
+		--sources ./src/checksum.c | \
+		awk -F',' '/DA:/ {found++; if($$2>0) hit++} END { \
+			percent = (found > 0) ? (hit/found)*100 : 0; \
+			msg = sprintf("\nTotal Coverage: %.2f%% (%d/%d lines hit)\n", percent, hit, found); \
+			print msg; \
+			if (ENVIRON["GITHUB_STEP_SUMMARY"] != "") { \
+				printf "### 📊 Coverage Report\n- **Status:** %s\n- **Percentage:** %.2f%%\n- **Details:** %d out of %d lines executed\n", \
+				(percent == 100 ? "✅ Pass" : "⚠️ Partial"), percent, hit, found >> ENVIRON["GITHUB_STEP_SUMMARY"]; \
+			} \
+		}'