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tsb: beat the first-pass size floors (tricks 666, pure 842)

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tricks 778->666: always_inline every single-call handler into the
[[noreturn]] reset entry (which pays no prologue, so their push/pop of
call-saved registers vanishes), walk the page pointer in Y (adiw, base
recovered as g_addr-page) instead of recomputing Z=base+offset, bring
the UART up in the two registers that are not already at their reset
value, and seed the activation counter as __uint24.

pure 896->842: TU-local internal linkage (proper hygiene, and it lets
the compiler inline the one-call handlers), a byte-wide activation
count, __uint24 timeout. Still one readable function per command.

asm unchanged at 498: its C++-expressible parts are already C++; the
core stays asm (the 666 B all-tricks tier is 168 B over — per-call ABI
tax, not a feature). All three cross-mode byte-identical, protocol green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
BlackMark
2026-07-19 20:15:49 +02:00
parent fc5433fd7d
commit 2b705ad130
3 changed files with 55 additions and 31 deletions
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8
tsb/tsb_pure.cpp
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@@ -24,6 +24,7 @@ using serial_t = dev::uart0<{.baud = 115200_Bd, .max_baud_error = 3_pct, .half_d
inline constexpr serial_t serial{};
namespace tsb {
namespace {
// The loader is purely polled — it never enables interrupts — so every SPM and
// EEPROM lock folds to nothing under this posture.
@@ -80,13 +81,13 @@ const std::uint8_t *flash_ptr(std::uint16_t addr)
}
// Stream `count` bytes to the host, from flash (LPM) or from EEPROM.
void send_flash(std::uint16_t addr, std::uint16_t count)
void send_flash(std::uint16_t addr, std::uint8_t count)
{
while (count--)
tx(avr::flash_load(flash_ptr(addr++)));
}
void send_eeprom(std::uint16_t addr, std::uint16_t count)
void send_eeprom(std::uint16_t addr, std::uint8_t count)
{
while (count--)
tx(ee::read(addr++));
@@ -238,7 +239,7 @@ gate password_gate()
// Activation: the host knocks three '@' inside a window whose length is the
// config page's timeout byte (floored so a corrupt page can never lock the
// loader out). An idle port times out and boots the application.
std::uint32_t idle = static_cast<std::uint32_t>(avr::flash_load(flash_ptr(app_end + 2)) | 16) << 16;
__uint24 idle = static_cast<__uint24>(avr::flash_load(flash_ptr(app_end + 2)) | 16) << 16;
std::uint8_t knocks = 0;
while (knocks < 3) {
if (auto byte = serial.read())
@@ -285,6 +286,7 @@ gate password_gate()
}
}
} // namespace
} // namespace tsb
// Reset lands here: BOOTRST vectors to the boot section base and .vectors is