Amey-Thakur Embedded memory constraints
A microcontroller gives you kilobytes, no MMU, and no swap: memory bugs do not throw, they corrupt. The discipline is knowing where every byte lives at link time and proving the stack fits before the field proves it does not.
Method
- Allocate statically; ban or bound the heap. Fixed-size pools, static buffers, and compile-time arrays for everything long-lived: heap use after init is where fragmentation slowly kills month-uptime devices. Where dynamic-ish behavior is needed, fixed-block pools (same-size chunks per object type) fragment nothing and fail loudly on exhaustion (the c-memory-safety arena idea, sized for kilobytes).
- Read the linker map as a budget. Per-section (.text,
.data, .bss, per-module) sizes tracked in CI with diffs per
PR (see bundle-size's twin): flash and RAM budgets with
headroom targets (~15-20% for growth and stack). The map also
catches the classics: accidental stdlib pull-ins (printf's
float support doubling .text), debug strings shipping to
production, duplicated const tables missing
PROGMEM/flash placement. - Size stacks by measurement, not vibes. Fill stacks with a
pattern at boot, measure high-water marks under worst-case
load (deep call paths, nested interrupts: see
interrupt-safe-code) per task (see rtos-task-design);
static analysis (
-fstack-usage, call-graph tools) bounds what tests miss. Enable hardware protection where available (MPU guard regions, stack canaries): a silent stack overflow into .bss is the least debuggable bug on a device (see embedded-debugging). - Choose data representations for the platform. Right-sized
integer types, packed flags, indices instead of pointers
(2 bytes vs 4/8, and serializable: see
entity-component-system's handle logic), lookup tables in
flash not RAM, strings as IDs resolved off-device where a
log pipeline exists (see sensor-data-handling's batching).
Alignment padding audit on structs (
-Wpaddedspot checks) recovers surprising bytes in arrays of thousands. - Make exhaustion behavior explicit. Every pool and queue has a stated full policy (drop-oldest for telemetry, reject-and-flag for commands: see backpressure's policy table, message-queues) and a counter observable in the field; out-of-memory in an embedded system must be a designed state, never a surprise, because there is no OOM-killer to blame.
- Keep debug and release honest. Asserts and logging cost RAM/flash: use link-time-removable levels (see log-levels), but keep the safety checks (bounds, pool exhaustion, watchdog kicks) in release; a build that only asserts in the lab ships its bugs silently (see defensive-programming's release-assert stance).
Boundaries
- Linux-class embedded (Pi-grade, with MMU) relaxes these rules toward ordinary systems programming (see c-memory-safety); this skill is for the MCU world beneath it.
- Rust-on-embedded moves several disciplines into the compiler (no-heap enforced by no_std, ownership: see rust-ownership) but stack sizing and linker budgeting remain manual.
- Ultra-low-power sleep states interact with RAM retention (which banks survive sleep); memory layout and power design are coupled decisions (see low-power-design).