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tsb: reimplement TinySafeBoot on libavr in three size tiers

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The native-UART fixed-baud TinySafeBoot protocol, ported onto libavr as a
crt-free boot-section loader, in three variants that trade clarity for size:

  tsb_pure   740 B  idiomatic C++: SRAM page buffer, separate flash/EEPROM
                    leaves, shared framing; the polled `unused` guard posture.
  tsb_tricks 658 B  unified runtime-flag paths (noinline/noclone), call-saved
                    global-register page walk — attributes only, no asm.
  tsb_asm    508 B  streaming store + hand-rolled UART/SPM/EEPROM/erase loops;
                    fits the 512 B boot section (BOOTSZ=11). Trims the optional
                    password gate and WDT-reset bail — unreachable in C++ with
                    both (hand-asm is ~15 % denser). Tiers 1-2 keep them and
                    live in the 1 KB section they fit.

All three are .text byte-identical across libavr's generated and reflect modes.
The CMake build strips the leaked -O3 (a Release build is silently -O3, not the
-Os this loader is measured against) and gates each variant's size against its
section. A simavr harness (test/device.c + test/tsbtest.py) drives the real wire
protocol over a pty and flashes the device; the size and protocol tests run in
ctest. Verified byte-for-byte against the reference tsbloader_adv (C#/mono):
activate, read info, flash write + verify.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
This commit is contained in:
BlackMark
2026-07-19 05:00:51 +02:00
parent 14ac91c815
commit 64c1e484b5
11 changed files with 1231 additions and 102 deletions
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44
CMakePresets.json Normal file
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{
"version": 8,
"configurePresets": [
{
"name": "base",
"hidden": true,
"generator": "Ninja",
"binaryDir": "${sourceDir}/build/${presetName}",
"toolchainFile": "$env{LIBAVR_ROOT}/cmake/avr-toolchain.cmake",
"cacheVariables": {
"CMAKE_BUILD_TYPE": "Release",
"CMAKE_EXPORT_COMPILE_COMMANDS": "ON",
"CMAKE_COLOR_DIAGNOSTICS": "ON"
}
},
{
"name": "atmega328p-generated",
"inherits": "base",
"cacheVariables": { "LIBAVR_MCU": "atmega328p", "LIBAVR_REFLECT": "OFF" }
},
{
"name": "atmega328p-reflect",
"inherits": "base",
"cacheVariables": { "LIBAVR_MCU": "atmega328p", "LIBAVR_REFLECT": "ON" }
}
],
"buildPresets": [
{ "name": "atmega328p-generated", "configurePreset": "atmega328p-generated" },
{ "name": "atmega328p-reflect", "configurePreset": "atmega328p-reflect" }
],
"workflowPresets": [
{
"name": "atmega328p-generated",
"steps": [
{ "type": "configure", "name": "atmega328p-generated" },
{ "type": "build", "name": "atmega328p-generated" },
{ "type": "test", "name": "atmega328p-generated" }
]
}
],
"testPresets": [
{ "name": "atmega328p-generated", "configurePreset": "atmega328p-generated", "output": { "outputOnFailure": true } }
]
}