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b008b37d49
Add a Tutorial tree that mirrors the roadmap from Phase 0 through Linux bring-up. Each phase and subphase gets a short learning note with consistent sections for context, goals, new concepts, mental model, learning tasks, pitfalls, tooling, testing, and references. The tutorial material is intentionally explanatory rather than implementation code. It gives a systems-oriented learner enough FPGA, SystemVerilog, RISC-V, firmware, and Linux bring-up context to approach each roadmap phase without turning the notes into copy-paste RTL.
50 lines
1.6 KiB
Markdown
50 lines
1.6 KiB
Markdown
# Phase 8.4 - Meaningful C Program
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## Context
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After minimal C works, write a program large enough to exercise stack, branches, calls,
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arrays, strings, and UART interaction.
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## Goals
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- Run an interactive or semi-interactive firmware.
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- Exercise real C control flow and memory behavior.
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- Build confidence before adding privilege and traps.
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## New Concepts
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- Stack frame: per-call storage for return address, locals, and saved registers.
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- Recursion: function calling itself, useful for stressing stack behavior.
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- Jump table: compiler-generated table for some switch statements.
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- Serial monitor: small firmware command interface over UART.
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## How To Think About It
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This is a system test, not a unit test. Failures can come from CPU, memory, compiler
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assumptions, or firmware bugs. Use it after smaller tests pass.
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## Learning Tasks
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- Trace one function call through prologue and epilogue.
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- Observe stack growth and confirm it stays within data memory.
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- Add one feature at a time to firmware and inspect generated assembly.
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## Pitfalls
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- Pulling in library functions accidentally.
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- Overflowing the tiny BRAM-backed stack.
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- Debugging optimized code before unoptimized code works.
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## Tooling And Testing
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- Use map files to understand memory usage.
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- Add firmware-visible test results through UART.
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- Keep a known-good simple firmware for regression comparisons.
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## References
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- RISC-V ELF psABI: https://github.com/riscv-non-isa/riscv-elf-psabi-doc
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- GNU ld map files: https://sourceware.org/binutils/docs/ld/Options.html
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- Embedded Artistry bare-metal articles: https://embeddedartistry.com/
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