pureboot 7: the same features in fewer words on every chip

Four cuts, none touching what the loader can do. The entry stub stops
re-doing the reset logic's own SP write where the datasheet guarantees
RAMEND (stack::hardware — the classic megas keep theirs). The autobaud
unit moves into GPIOR2:GPIOR1 wherever the chip has the pair: one-word
accesses, no RAM object, and the host's measured-clock peek follows it
by version and geometry. 'J' rides the unified decode, carrying a
selector it ignores so its address is the same two reads as every other
command — the tool sends the bare form to older residents. run_app stops
insisting on a body of its own. The fleet lands at 358–410 B stock and
438–474 B autobaud; the tightest image in the space — the 1284s'
autobaud on a USART's own pins with the OSCCAL trim — drops from 510 to
484 of its 512. Every chip's suite is green on the wire that changed,
and the README's table is machine-checked against the built images.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/check_unit.cmake

@@ -1,7 +1,10 @@
-# Asserts the autobaud loader's measured unit is the first RAM object: the
-# host tool reads the bit period from ram_start (--info's measured clock), so
-# the unit's address is wire contract. Run as
-#   cmake -DOBJDUMP=... -DELF=... -DRAM_START=<data address> -P check_unit.cmake
+# Asserts the autobaud loader's measured unit sits where the host will read
+# it (--info's measured clock — the address is wire contract). Two homes: on
+# a chip with the GPIOR pair the unit lives there and the image must carry no
+# RAM word for it at all; elsewhere it is the first RAM object at SRAM start.
+# Run as
+#   cmake -DOBJDUMP=... -DELF=... -DRAM_START=<data address> [-DGPIOR=<data address>]
+#         -P check_unit.cmake
 
 execute_process(COMMAND ${OBJDUMP} -t ${ELF} OUTPUT_VARIABLE _syms RESULT_VARIABLE _res)
 if(NOT _res EQUAL 0)
@@ -9,7 +12,17 @@ if(NOT _res EQUAL 0)
 endif()
 
 # The symbol line: "00800100 l     O .noinit  00000002 <mangled>unit_E".
-string(REGEX MATCH "\n0*([0-9a-f]+)[^\n]+[ \t][^ \t\n]*unit_[^ \t\n]*\n" _line "${_syms}")
+string(REGEX MATCH "\n0*([0-9a-f]+)[^\n]+[ \t][^ \t\n]*unit_E\n" _line "${_syms}")
+
+if(GPIOR)
+	if(_line)
+		message(FATAL_ERROR "unit_ RAM symbol present although the unit's home is GPIOR ${GPIOR} — "
+		                    "the host peeks the pair, and a RAM copy would be dead weight")
+	endif()
+	message(STATUS "no unit_ RAM object — the unit lives in the GPIOR pair at ${GPIOR}")
+	return()
+endif()
+
 if(NOT _line)
 	message(FATAL_ERROR "no unit_ symbol in ${ELF} — is this the autobaud loader?")
 endif()

test/pbautobaud.py

@@ -64,8 +64,9 @@ def main():
             for needed in ("version", "signature", "fuses", "verify:", "stays"):
                 if needed not in out:
                     fail(f"{label}: session output lacks {needed!r}\n{out}")
-            # The measured clock, decoded from the unit at ram_start. The
-            # runner's clock is exact, so the figure must land inside the
+            # The measured clock, decoded from the unit at whichever home this
+            # version keeps it in. The runner's clock is exact, so the figure
+            # must land inside the
             # encoding's own envelope: the loader floors the bit period to
             # 4-cycle spin granules after an 8-cycle discount, and the edge
             # poll can shave a few cycles more — one granule of slack below