avr/bootloader
1
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

pureboot: the device — one pure C++ source, 512 bytes, every chip

Browse Source 
No inline assembly, no global register variables; libavr does the
datasheet work. The device speaks primitives — flash read/page-program,
EEPROM read/write, fuse read, info block, EEPROM-resident activation
timeout, hand-over — and verify, erase, reset-vector surgery, and
timeout configuration live in the host tool. 490 B on the ATtiny13A,
510 B on the ATtiny85, 484 B on the ATmega328P, each linked into the
top 512 bytes of flash; per-chip size tests gate all three.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
This commit is contained in:
BlackMark
2026-07-20 05:33:28 +02:00
parent 74d8b92885
commit 47990349a4
4 changed files with 515 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files

57
CMakeLists.txt
View File

@@ -19,13 +19,13 @@ if(PROJECT_IS_TOP_LEVEL)
add_compile_options(-Werror) # warnings are errors for the port's own code
enable_testing()
# The behavioral test drives the real TinySafeBoot wire protocol over a
# simavr pty (as the host tools do) and actually flashes the device. The
# runner is a host program built at configure time against libsimavr; if it
# or Python is missing, only the size tests run.
# The behavioral tests drive the real wire protocols over a simavr pty
# (as the host tools do) and actually flash the device. The runners are
# host programs built at configure time against libsimavr; if they or
# Python are missing, only the size tests run.
find_program(_host_cc NAMES cc gcc)
find_package(Python3 COMPONENTS Interpreter)
if(_host_cc AND Python3_FOUND)
if(_host_cc AND Python3_FOUND AND LIBAVR_MCU STREQUAL "atmega328p")
set(TSB_DEVICE ${CMAKE_BINARY_DIR}/tsb_device)
execute_process(
COMMAND ${_host_cc} -O2 -I/usr/include/simavr -I/usr/include/simavr/parts
@@ -90,6 +90,47 @@ function(add_tsb_variant name bytes)
endif()
endfunction()
add_tsb_variant(tsb_asm 512)
add_tsb_variant(tsb_pure 1024)
add_tsb_variant(tsb_tricks 1024)
# The tsb tiers reimplement the ATmega328P-only reference protocol; the other
# chips build pureboot alone.
if(LIBAVR_MCU STREQUAL "atmega328p")
add_tsb_variant(tsb_asm 512)
add_tsb_variant(tsb_pure 1024)
add_tsb_variant(tsb_tricks 1024)
endif()
# pureboot — the pure-constraint port (see pureboot/README.md): one source,
# no inline assembly, no global register variables, every libavr chip, 512
# bytes each. The loader owns the top 512 bytes of flash on every chip; the
# application entry symbol is address 0 on the mega (reset re-vectors to the
# loader through BOOTRST, so word 0 stays the application's own vector) and
# the trampoline word just below the loader on the tinies (host-side vector
# surgery points it at the application). --pmem-wrap-around models AVR's
# modulo-flash PC where the flash is big enough to need it.
if(LIBAVR_MCU STREQUAL "attiny13a")
set(_pb_flash 1024)
set(_pb_wrap "")
elseif(LIBAVR_MCU STREQUAL "attiny85")
set(_pb_flash 8192)
set(_pb_wrap -Wl,--pmem-wrap-around=8k)
else()
set(_pb_flash 32768)
set(_pb_wrap -Wl,--pmem-wrap-around=32k)
endif()
math(EXPR _pb_base "${_pb_flash} - 512")
math(EXPR _pb_base_hex "${_pb_base}" OUTPUT_FORMAT HEXADECIMAL)
if(LIBAVR_MCU STREQUAL "atmega328p")
set(_pb_app 0)
else()
math(EXPR _pb_app "${_pb_base} - 2")
endif()
add_executable(pureboot pureboot/pureboot.cpp)
target_link_libraries(pureboot PRIVATE libavr)
target_link_options(pureboot PRIVATE -nostartfiles -Wl,--section-start=.text=${_pb_base_hex}
-Wl,--defsym=pureboot_app=${_pb_app} ${_pb_wrap})
add_custom_command(TARGET pureboot POST_BUILD COMMAND ${CMAKE_SIZE} $<TARGET_FILE:pureboot>)
if(PROJECT_IS_TOP_LEVEL)
add_test(NAME pureboot.size
COMMAND ${CMAKE_COMMAND} -DSIZE_TOOL=${CMAKE_SIZE} -DELF=$<TARGET_FILE:pureboot>
-DLIMIT=512 -P ${CMAKE_CURRENT_SOURCE_DIR}/test/check_size.cmake)
endif()