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pureboot: the detail reaches become the library's own API

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The three things this repo took from under libavr's counter are now over
it, and the local copies fold away. The USART release on a software
link's pins is the library's init contract (its guard here becomes a
deletion, byte-identical images held by the gate); the WDRF routing test
is power::peek_reset_cause().watchdog instead of a hand lookup of the
flag's register; the tsb tiers' baud arithmetic is the public solver.
libavr pin advances over those three additions.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
This commit is contained in:
BlackMark
2026-07-28 16:12:35 +02:00
parent c535c4756c
commit e23e535f86
5 changed files with 5 additions and 35 deletions
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2
libavr

Submodule libavr updated: 26b80e262d...911a87538f

32
pureboot/pureboot.cpp
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@@ -38,13 +38,6 @@ using dev = avr::device<{.clock = avr::hertz_t{PUREBOOT_CLOCK_HZ}}>;
constexpr avr::baud_t wire_baud{PUREBOOT_BAUD};
#endif
// The watchdog reset flag's home: MCUSR, or the classic megas' MCUCSR.
consteval std::int16_t wdrf_field()
{
auto reg = std::string_view{avr::hw::db.regs[static_cast<std::size_t>(avr::power::detail::reset_reg())].name};
return avr::hw::db.field_index(reg, "WDRF");
}
// The loader owns the top 512 bytes; a staging copy goes in the slot below.
// Chips without a hardware boot section — the tinies and the m48s, whose SPM
// runs from anywhere (Atmel-8271 §26) — keep the application's relocated
@@ -174,27 +167,6 @@ constexpr char usart_digit = '0' + PUREBOOT_USART;
constexpr char usart_digit = '0';
#endif
// Release a hardware USART the application may have left enabled onto a
// bit-banged link's pins. A software transmitter drives its TX pin through the
// port register, but while that USART's TXEN is set the USART owns the pin and
// the port write does nothing — the loader would receive and obey yet never
// answer. Writing UCSRnB zero hands the pin back to the port. Guarded on the
// pin actually being a USART's TXD, so a link on non-USART pins emits nothing.
template <char Inst, avr::io::pin Tx>
[[gnu::always_inline]] inline void release_usart_on()
{
if constexpr (avr::uart::has_usart<Inst>())
if constexpr (avr::uart::detail::usart_pin<Inst>("TXD") == Tx)
avr::hw::reg_impl<avr::uart::detail::ureg<Inst, "UCSR#B">()>::write(0);
}
template <avr::io::pin Tx>
[[gnu::always_inline]] inline void release_usarts_on()
{
release_usart_on<'0', Tx>();
release_usart_on<'1', Tx>();
}
template <avr::hertz_t C, avr::baud_t B>
struct hardware_link {
using uart = avr::uart::usart<usart_digit, C, {.baud = B, .max_baud_error = 2.5_pct}>;
@@ -241,7 +213,6 @@ struct software_link {
static void init()
{
avr::init<rx_t, tx_t>();
release_usarts_on<avr::PUREBOOT_TX>();
}
static bool pending()
@@ -275,7 +246,6 @@ struct autobaud_link {
static void init()
{
avr::init<uart>();
release_usarts_on<avr::PUREBOOT_TX>();
}
static std::uint8_t rx()
@@ -498,7 +468,7 @@ void fill_page(std::uint8_t bank, std::uint16_t at)
#endif
// A watchdog reset belongs to the application, whose watchdog stays forced
// on until it clears WDRF — no activation window in its way.
if (avr::hw::field_impl<wdrf_field()>::test())
if (avr::power::peek_reset_cause().watchdog)
run_app();
link::init();

2
tsb/tsb_asm.cpp
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@@ -65,7 +65,7 @@ constexpr std::uint8_t comm_window = 200;
constexpr std::uint16_t build_date = 26 * 512 + 7 * 32 + 20;
// Fixed 115200 8N1; the library solves UBRR + U2X from clock and baud.
constexpr auto baud = avr::uart::detail::solve_baud(16_MHz, 115200_Bd);
constexpr auto baud = avr::uart::solve_baud(16_MHz, 115200_Bd);
// The 16-byte device-info block, streamed out on activation.
// clang-format off

2
tsb/tsb_policy.cpp
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@@ -200,7 +200,7 @@ extern "C" [[noreturn]] void tsb_app(); // the application's reset vector: --def
// only the divisor low byte and U2X0 need a store. The solver still does
// the datasheet work; the asserts pin the reset-state assumptions.
{
constexpr auto sol = avr::uart::detail::solve_baud(dev::clock, 115200_Bd);
constexpr auto sol = avr::uart::solve_baud(dev::clock, 115200_Bd);
static_assert(sol.u2x && sol.ubrr < 256, "lean bring-up writes UBRR0L only, with U2X0");
avr::hw::reg<"UBRR0">::write(static_cast<std::uint8_t>(sol.ubrr));
avr::hw::ucsr0a::write(avr::hw::ucsr0a::u2x0(1));

2
tsb/tsb_tricks.cpp
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@@ -65,7 +65,7 @@ constexpr std::uint8_t comm_window = 200;
constexpr std::uint16_t build_date = 26 * 512 + 7 * 32 + 20;
// Fixed 115200 8N1; the library solves UBRR + U2X from clock and baud.
constexpr auto baud = avr::uart::detail::solve_baud(16_MHz, 115200_Bd);
constexpr auto baud = avr::uart::solve_baud(16_MHz, 115200_Bd);
// The 16-byte device-info block, streamed out on activation.
// clang-format off