diff --git a/libavr b/libavr
index 26b80e2..911a875 160000
--- a/libavr
+++ b/libavr
@@ -1 +1 @@
-Subproject commit 26b80e262dcf475fdb3c647e43ade1e2ef85d04c
+Subproject commit 911a87538f2dc99a22ac0b2faa9434ad6e438362
diff --git a/pureboot/pureboot.cpp b/pureboot/pureboot.cpp
index 964d8ea..4665b19 100644
--- a/pureboot/pureboot.cpp
+++ b/pureboot/pureboot.cpp
@@ -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();
diff --git a/tsb/tsb_asm.cpp b/tsb/tsb_asm.cpp
index 7cf105c..1594939 100644
--- a/tsb/tsb_asm.cpp
+++ b/tsb/tsb_asm.cpp
@@ -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
diff --git a/tsb/tsb_policy.cpp b/tsb/tsb_policy.cpp
index fb061c9..f5cedf2 100644
--- a/tsb/tsb_policy.cpp
+++ b/tsb/tsb_policy.cpp
@@ -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));
diff --git a/tsb/tsb_tricks.cpp b/tsb/tsb_tricks.cpp
index 53b0dcc..84d4684 100644
--- a/tsb/tsb_tricks.cpp
+++ b/tsb/tsb_tricks.cpp
@@ -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