build: presets.generated runs, and the tier list lives in the sources

make_presets.py documented a presets.generated test that was never registered,
so a hand edit to CMakePresets.json could drift unseen; it is registered now,
and the generator names its encoding and line ending so a regeneration on
Windows writes the same file. The CMake comment's per-tier essay repeated each
source's own header - and claimed naked stubs where all four use
startup::entry - so it points there instead, and the flash size the boot base
and the wrap-around both follow from is named once.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CMakeLists.txt

@@ -34,9 +34,8 @@ if(PROJECT_IS_TOP_LEVEL)
 	# distribution's compiler speaks in full).
 	#
 	# **A host that cannot build it registers those tests anyway and skips
-	# them.** They used to be left out, which makes the suite a different size
-	# on a different machine - and a suite whose size is a property of the
-	# machine is one nothing can be compared against.
+	# them**: leaving them out would make the suite's size a property of the
+	# machine, and such a suite is one nothing can be compared against.
 	set(TSB_DEVICE ${CMAKE_BINARY_DIR}/tsb_device)
 	find_program(_host_cxx NAMES c++ g++)
 	set(_tsb_absent "${LIBAVR_NO_PYTHON}")
@@ -66,6 +65,11 @@ if(PROJECT_IS_TOP_LEVEL)
 	if(_tsb_absent)
 		message(STATUS "the protocol tests skip here - ${_tsb_absent}")
 	endif()
+
+	# CMakePresets.json is generated; the gate holds it to its generator.
+	libavr_launcher(_presets_python "${LIBAVR_NO_PYTHON}" ${Python3_EXECUTABLE})
+	add_test(NAME presets.generated
+	         COMMAND ${_presets_python} ${CMAKE_CURRENT_SOURCE_DIR}/tools/make_presets.py --check)
 endif()
 
 # The ELF is only a container (symbols, section headers) and is never flashed -
@@ -82,48 +86,27 @@ function(add_image_outputs name)
 	                           $<TARGET_FILE:${name}> $<TARGET_FILE:${name}>.bin)
 endfunction()
 
-# The TinySafeBoot protocol reimplemented on libavr in variants that trade
-# clarity for size. Each links into the ATmega328P boot section (BOOTSZ selects
-# its size; BOOTRST vectors a reset to its base) with -nostartfiles - a polled
-# loader has no use for the crt or the vector table. The entry sits in
-# .vectors, laid first, and runs - avr::startup::entry on the policy tier,
-# the experiment tiers' own naked stubs elsewhere, each documented in its
-# source. The boot base is FLASHEND+1 minus the section size; the linker
-# section-start and the source's boot_bytes agree. tsb_app is
-# the application's reset vector, pinned to 0 here so the loaders jump to a
-# named function; --pmem-wrap-around lets relaxation turn that absolute jump
-# into the wrapped rjmp AVR's modulo-flash PC actually executes.
-# All four implement the full oracle feature set (see oracle/README.md):
-# watchdog bail, one-wire half-duplex, config-page activation timeout, password
-# gate, emergency erase, config/flash/EEPROM read-write. They differ only in how,
-# and the size gradient is the cost of that "how".
-#   tsb_asm    - the tricks tier's C++ with exactly two routines in asm: the
-#                 bounded rx and the page-store loop, the two whose remaining
-#                 cost is the C ABI itself. Everything else, bring-up to
-#                 dispatch, is C++ on libavr.
-#   tsb_tricks - no asm at all: the whole-loader register allocation lives in
-#                 global register variables (Y walks the page pointer), every
-#                 helper is a tiny noinline primitive placed by the
-#                 global-register store rules, pages stream straight to
-#                 SPM/EEPROM.
-#   tsb_pure   - pure idiomatic libavr, one function per command, TU-local
-#                 (internal linkage), streaming (no SRAM page buffer).
-#   tsb_policy - the policy floor: no inline assembly and no global register
-#                 variables, which is philosophy #5's own bound, and the
-#                 measured evidence that the 512 B fit is a property of the
-#                 mechanisms it bans.
-#
-# What each measures is oracle/README.md's table, which is the one place the
-# four numbers and the hand-written loader's own are compared.
-#
+# The TinySafeBoot protocol reimplemented on libavr in four tiers that trade
+# clarity for size, each with the full oracle feature set; each source's header
+# says what its tier is allowed, and oracle/README.md compares what they
+# measure. Each links into the ATmega328P boot section (BOOTSZ selects its
+# size; BOOTRST vectors a reset to its base) with -nostartfiles - a polled
+# loader has no use for the crt or the vector table - and its entry sits in
+# .vectors, laid first. The boot base is the flash size minus the section size;
+# the linker section-start and the source's boot_bytes agree. tsb_app is the
+# application's reset vector, pinned to 0 here so the loaders jump to a named
+# function; --pmem-wrap-around lets relaxation turn that absolute jump into the
+# wrapped rjmp AVR's modulo-flash PC actually executes.
+set(TSB_FLASH_KIB 32)
+
 # add_tsb_variant(<name> <boot-section-bytes>)
 function(add_tsb_variant name bytes)
-	math(EXPR base_dec "32768 - ${bytes}")
+	math(EXPR base_dec "${TSB_FLASH_KIB} * 1024 - ${bytes}")
 	math(EXPR base_hex "${base_dec}" OUTPUT_FORMAT HEXADECIMAL)
 	add_executable(${name} tsb/${name}.cpp)
 	target_link_libraries(${name} PRIVATE libavr)
 	target_link_options(${name} PRIVATE -nostartfiles -Wl,--section-start=.text=${base_hex}
-	                    -Wl,--defsym=tsb_app=0 -Wl,--pmem-wrap-around=32k)
+	                    -Wl,--defsym=tsb_app=0 -Wl,--pmem-wrap-around=${TSB_FLASH_KIB}k)
 	add_custom_command(TARGET ${name} POST_BUILD COMMAND ${CMAKE_SIZE} $<TARGET_FILE:${name}>)
 	add_image_outputs(${name})
 	if(PROJECT_IS_TOP_LEVEL)

tools/make_presets.py

@@ -75,12 +75,12 @@ def main():
     rendered = json.dumps(presets, indent=1) + "\n"
     path = os.path.join(os.path.dirname(os.path.abspath(__file__)), "..", "CMakePresets.json")
     if "--check" in sys.argv[1:]:
-        current = open(path).read() if os.path.exists(path) else ""
+        current = open(path, encoding="utf-8").read() if os.path.exists(path) else ""
         if current != rendered:
             print("CMakePresets.json does not match its generator - run tools/make_presets.py")
             return 1
         return 0
-    with open(path, "w") as f:
+    with open(path, "w", encoding="utf-8", newline="\n") as f:
         f.write(rendered)
     print(f"{len(CHIPS)} chips, {len(REFLECT_SPOT)} reflect: {os.path.normpath(path)}")
     return 0