/resource-optimization-lowend

name: resource-optimization-lowend
description: Resource optimization skill for constrained embedded targets. Use when reducing flash/RAM usage, analyzing stack depth, reading linker map files, or tuning size vs speed on MCUs. Activates on queries about firmware size optimization, linker map, stack usage, -Os, flash RAM budget, or bloat analysis.

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