--- title: Dirty Optimization Secrets (C for Playdate) | daily.dev description: Advanced C optimization techniques for the Playdate handheld's Cortex M7 CPU, discovered while building a full-speed Game Boy emulator. Covers instruction... canonical: https://daily.dev/posts/dirty-optimization-secrets-c-for-playdate--oyztdgflb twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Dirty Optimization Secrets (C for Playdate) | daily.dev og:description: Advanced C optimization techniques for the Playdate handheld's Cortex M7 CPU, discovered while building a full-speed Game Boy emulator. Covers instruction... og:url: https://daily.dev/posts/dirty-optimization-secrets-c-for-playdate--oyztdgflb og:image: https://api.daily.dev/og/posts/oyztdgFlB.png og:image:alt: Dirty Optimization Secrets (C for Playdate) og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Dirty Optimization Secrets (C for Playdate) **[Lobsters](https://daily.dev/sources/lobsters)** · 11 min read · 0 upvotes · 0 comments ## Summary Advanced C optimization techniques for the Playdate handheld's Cortex M7 CPU, discovered while building a full-speed Game Boy emulator. Covers instruction cache constraints (using -Os instead of -O3, keeping core loops under 4-16KB), custom linker scripts to control code placement, using nm to inspect symbol addresses, exploiting tightly-coupled memory (TCM) for stack and code acceleration, cache-line alignment tricks to avoid a 'performance lottery' of inconsistent build speeds, branch prediction table alignment, and prefetching for pointer-indirection-heavy code. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### Why would using -Os instead of -O3 make C code faster on an embedded Cortex M7 device like the Playdate? Because the Playdate's instruction cache is very small (4KB on Rev A, reportedly 16KB on Rev B), so code size matters more than instruction count. Compiling with -Os keeps core hot-loop code compact enough to fit in the instruction cache, which can make it run faster than -O3 output even though -O3 often produces fewer, more optimized instructions per operation. _Developers tuning tight loops on constrained hardware compare compiler flag trade-offs like this on daily.dev._ ### How can I keep a struct permanently on the stack in C when I don't control main and can't allocate it normally? Use the low, unused end of the stack as a manual memory pool: call __builtin_frame_address(0) inside the event handler at initialization to get the high-address end of the stack, then subtract a safe margin (around 0x2180 bytes) to reach the low end, avoiding overflow. Store data there with guard canaries at both ends, checked each update, to detect stack overflow corruption. _Anyone squeezing extra speed from embedded C stacks can track tricks like this on daily.dev._ ### How do I copy C functions into ITCM (tightly-coupled memory) at runtime on a Cortex M7 chip without crashing? Mark functions with a custom section attribute plus __attribute__((short_call)), expose __itcm_start and __itcm_end linker symbols, then memcpy the byte range between them to the destination, ensuring the destination address is congruent mod 2 to the original since the Cortex M7 uses the low bit of function pointers for Thumb/ARM mode. Functions called from outside the region need __attribute__((longcall)), and the icache must be flushed after copying. _Embedded developers chasing Cortex M7 speedups can follow techniques like this on daily.dev._ ## Similar posts on daily.dev - [Binary Obfuscation that Doesn't Kill LTO: A Recap of My Thotcon Talk](https://daily.dev/posts/binary-obfuscation-that-doesn-t-kill-lto-a-recap-of-my-thotcon-talk-5st70tkez) · Hacker News · 0 upvotes · 0 comments - [Building a Tiny 3D Renderer for a Tiny Handheld](https://daily.dev/posts/building-a-tiny-3d-renderer-for-a-tiny-handheld-ncrfzmr8j) · Hacker News · 0 upvotes · 0 comments --- Tags: [#performance](https://daily.dev/tags/performance), [#c](https://daily.dev/tags/c), [#embedded](https://daily.dev/tags/embedded) [View this post on daily.dev](https://daily.dev/posts/dirty-optimization-secrets-c-for-playdate--oyztdgflb) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Dirty Optimization Secrets (C for Playdate)","url":"https://daily.dev/posts/dirty-optimization-secrets-c-for-playdate--oyztdgflb","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/dirty-optimization-secrets-c-for-playdate--oyztdgflb"},"datePublished":"2026-09-30T20:58:46.344Z","dateModified":"2026-09-30T20:59:13.375Z","description":"Advanced C optimization techniques for the Playdate handheld's Cortex M7 CPU, discovered while building a full-speed Game Boy emulator. 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