mohitmishra786/resource-optimization-lowend

Resource Optimization (Low-End Systems)

Purpose

Guide agents through flash and RAM optimization on constrained devices: compiler size flags, linker map analysis, stack usage measurement, dead code elimination, and size-vs-speed tradeoffs — for bare-metal and small RTOS images.

When to Use

• Firmware exceeds flash budget
• Stack overflow in production only
• Choosing -Os vs -O2 on MCU
• Finding unexpected .rodata or .bss growth

Workflow

1. Size measurement toolchain

arm-none-eabi-size -A firmware.elf
arm-none-eabi-objdump -h firmware.elf
nm --size-sort -S firmware.elf | tail -20

2. Linker map file

/* linker.ld */
OUTPUT_FORMAT("elf32-littlearm")
ENTRY(Reset_Handler)

SECTIONS
{
  /* ... */
}

/* Generate map */
/* gcc ... -Wl,-Map=firmware.map */

grep -E '\.text|\.rodata|\.data|\.bss' firmware.map | head

Identify largest symbols and unexpected library pull-in.

3. Compiler flags

| Flag | Effect | |------|--------| | -Os | Size-first optimization | | -ffunction-sections -fdata-sections | Per-symbol sections | | -Wl,--gc-sections | Drop unused sections | | -flto | Cross-TU dead code elimination | | -specs=nano.specs | Smaller newlib (GCC ARM) |

CFLAGS += -Os -ffunction-sections -fdata-sections
LDFLAGS += -Wl,--gc-sections -Wl,--print-memory-usage

4. Stack analysis

# Static (if built with -fstack-usage)
find . -name '*.su' -exec cat {} \;

# Linker stack symbol
grep _estack firmware.map

Runtime: fill stack with pattern (0xDEADBEEF), run tests, scan high-water mark. FreeRTOS: uxTaskGetStackHighWaterMark.

5. RAM categories

| Section | Tactic | |---------|--------| | .bss | Shrink buffers; pool allocators | | .data | Move const to flash (const → .rodata) | | Heap | Avoid malloc; fixed pools | | Stack | Reduce nesting; smaller ISR stacks |

6. Size vs speed decision

Hot path in ISR or 1 kHz loop?
├── Yes → -O2 for that file (#pragma GCC optimize)
└── No  → -Os globally

7. Agent usage

/resource-optimization-lowend Find top 10 flash consumers in firmware.map and suggest -gc-sections fixes

Common Problems

| Symptom | Cause | Fix | |---------|-------|-----| | printf pulls 20+ KB | Full newlib printf | _write retarget; tiny printf | | --gc-sections broke IRQ | Section collected | KEEP() in linker script | | Stack overflow late | Deep call + IRQ nest | Measure HW stack; increase _estack | | RAM zero but big ELF | .data not loaded | Check VMA/LMA | | LTO link fail | Mixed compiler versions | Same GCC for all objects |

Related Skills

• skills/embedded/linker-scripts — MEMORY/Sections layout
• skills/baremetal/baremetal-startup — stack symbol
• skills/baremetal/low-power-embedded — RAM retention
• skills/compilers/gcc — optimization flags
• skills/rust/rust-no-std — embedded Rust size patterns