diff --git a/libavr b/libavr
index f5d7122..56337f3 160000
--- a/libavr
+++ b/libavr
@@ -1 +1 @@
-Subproject commit f5d71225a2bcd2424f6a7cbaee09b9b3426a05ba
+Subproject commit 56337f37de2f369a6196f8bfdf0b7165b8ea61bf
diff --git a/pureboot/pureboot.cpp b/pureboot/pureboot.cpp
index 03129fd..95414ba 100644
--- a/pureboot/pureboot.cpp
+++ b/pureboot/pureboot.cpp
@@ -162,14 +162,14 @@ constexpr std::uint8_t bank_shift = 16 - slot_shift;
 #define PUREBOOT_TX pb1
 #endif
 #if defined(PUREBOOT_USART)
-constexpr char usart_digit = '0' + PUREBOOT_USART;
+constexpr int usart_unit = PUREBOOT_USART;
 #else
-constexpr char usart_digit = '0';
+constexpr int usart_unit = 0;
 #endif
 
 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}>;
+	using uart = avr::uart::usart<usart_unit, C, {.baud = B, .max_baud_error = 2.5_pct}>;
 
 	// The compiled idle poll: lds UCSR0A (2), sbrc skipping the exit (2),
 	// sbiw + sbci + sbci + brne (6).
@@ -270,12 +270,12 @@ struct autobaud_link {
 #if defined(PUREBOOT_AUTOBAUD)
 using link = autobaud_link;
 #elif defined(PUREBOOT_USART)
-static_assert(avr::uart::has_usart<usart_digit>(), "PUREBOOT_USART selects a hardware USART this chip does not have");
+static_assert(avr::uart::has_usart<usart_unit>(), "PUREBOOT_USART selects a hardware USART this chip does not have");
 using link = hardware_link<dev::clock, wire_baud>;
 #elif defined(PUREBOOT_SOFT_SERIAL)
 using link = software_link<dev::clock, wire_baud>;
 #else
-using link = std::conditional_t<avr::uart::has_usart<usart_digit>(), hardware_link<dev::clock, wire_baud>,
+using link = std::conditional_t<avr::uart::has_usart<usart_unit>(), hardware_link<dev::clock, wire_baud>,
                                 software_link<dev::clock, wire_baud>>;
 #endif
 
diff --git a/test/pbapp.cpp b/test/pbapp.cpp
index 0031238..a619a48 100644
--- a/test/pbapp.cpp
+++ b/test/pbapp.cpp
@@ -50,7 +50,7 @@ consteval bool use_hardware()
 #if defined(PUREBOOT_SOFT_SERIAL)
 	return false;
 #else
-	return avr::hw::db.has_instance("USART0") || avr::hw::db.has_instance("USART");
+	return avr::uart::has_usart<0>();
 #endif
 }
 
@@ -63,7 +63,7 @@ struct link {
 #else
 	static constexpr avr::baud_t baud{115200};
 #endif
-	using tx_t = avr::uart::usart<'0' + PUREBOOT_USART, C, {.baud = baud, .max_baud_error = 2.5_pct}>;
+	using tx_t = avr::uart::usart<PUREBOOT_USART, C, {.baud = baud, .max_baud_error = 2.5_pct}>;
 	static void tx(char c)
 	{
 		tx_t::write(static_cast<std::uint8_t>(c));
diff --git a/tsb/tsb_asm.cpp b/tsb/tsb_asm.cpp
index 1594939..a01c402 100644
--- a/tsb/tsb_asm.cpp
+++ b/tsb/tsb_asm.cpp
@@ -263,7 +263,7 @@ extern "C" [[noreturn]] void tsb_app(); // the application's reset vector: --def
 	// 0, and rx()/tx() raise RXEN0/TXEN0 on first use — only the divisor low
 	// byte and U2X0 need a store. The library still does the datasheet work.
 	static_assert(baud.u2x && baud.ubrr < 256, "lean bring-up writes UBRR0L only, with U2X0");
-	hw::reg<"UBRR0">::write(static_cast<std::uint8_t>(baud.ubrr));
+	hw::ubrr0::write(static_cast<std::uint8_t>(baud.ubrr));
 	hw::ucsr0a::write(hw::ucsr0a::u2x0(1));
 	// General-purpose registers are undefined at power-on (no crt zeroes them);
 	// the direction latch must start "not receiving" so the first rx() enables
diff --git a/tsb/tsb_policy.cpp b/tsb/tsb_policy.cpp
index f5cedf2..565f553 100644
--- a/tsb/tsb_policy.cpp
+++ b/tsb/tsb_policy.cpp
@@ -202,7 +202,7 @@ extern "C" [[noreturn]] void tsb_app(); // the application's reset vector: --def
 	{
 		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::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 84d4684..e2cc524 100644
--- a/tsb/tsb_tricks.cpp
+++ b/tsb/tsb_tricks.cpp
@@ -240,7 +240,7 @@ extern "C" [[noreturn]] void tsb_app(); // the application's reset vector: --def
 	// 0, and rx()/tx() raise RXEN0/TXEN0 on first use — only the divisor low
 	// byte and U2X0 need a store. The library still does the datasheet work.
 	static_assert(baud.u2x && baud.ubrr < 256, "lean bring-up writes UBRR0L only, with U2X0");
-	hw::reg<"UBRR0">::write(static_cast<std::uint8_t>(baud.ubrr));
+	hw::ubrr0::write(static_cast<std::uint8_t>(baud.ubrr));
 	hw::ucsr0a::write(hw::ucsr0a::u2x0(1));
 	// General-purpose registers are undefined at power-on (no crt zeroes them);
 	// the direction latch must start "not receiving" so the first rx() enables