BlackMarkandClaude Opus 5.5
e395c0344f
tsb/tsb.hpp holds the link, the handshake and command bytes, the guard policy and SPM interlock, the boot geometry, act_min/comm_window and a consteval builder for the 16-byte info block, whose BUILDSTATE and ATmega marker bytes are now named rather than commented. Every tier's image is byte-identical to before. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
107 lines
3.5 KiB
C++
107 lines
3.5 KiB
C++
// The TinySafeBoot native-UART fixed-baud protocol, as every tier speaks it:
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// the link, the handshake and command bytes, the boot geometry and the
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// device-info block the host reads on activation.
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#pragma once
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#include <libavr/libavr.hpp>
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namespace tsb {
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using namespace avr::literals;
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namespace spm = avr::spm;
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namespace ee = avr::eeprom;
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constexpr auto clock = 16_MHz;
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constexpr auto baud_rate = 115200_Bd;
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// Fixed 8N1; the library solves UBRR + U2X from clock and baud.
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constexpr auto baud = avr::uart::solve_baud(clock, baud_rate, 8, avr::uart::parity::none);
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// One bit time on the wire: the turn-around a shared-line peer needs to stop
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// driving before this one starts.
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constexpr auto guard_cycles = static_cast<std::uint32_t>(clock.hz / baud.actual);
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// The loader is purely polled - it never enables interrupts - so every SPM and
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// EEPROM lock folds to nothing under this posture.
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constexpr auto off = avr::irq::guard_policy::unused;
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// Strict request/response: every SPM operation is waited out before the next
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// byte moves, so no flash operation is ever in flight at an EEPROM access -
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// the write procedure's step 2 has nothing to guard, the omission the
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// datasheet grants (DS40002061B section 8.6.3).
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constexpr auto no_spm = ee::spm_interlock::omitted;
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constexpr std::uint8_t confirm = '!';
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constexpr std::uint8_t request = '?';
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constexpr std::uint8_t knock = '@';
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constexpr std::uint8_t activation_knocks = 3;
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namespace command {
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constexpr std::uint8_t read_flash = 'f';
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constexpr std::uint8_t write_flash = 'F';
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constexpr std::uint8_t read_eeprom = 'e';
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constexpr std::uint8_t write_eeprom = 'E';
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constexpr std::uint8_t read_config = 'c';
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constexpr std::uint8_t write_config = 'C';
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} // namespace command
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// The lockout-proof floor for the receive window: the oracle's F_CPU/1MHz.
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constexpr auto act_min = static_cast<std::uint8_t>(clock.hz / 1'000'000);
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// Post-activation window: the host gets seconds, not milliseconds, mid-session.
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constexpr std::uint8_t comm_window = 200;
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constexpr std::uint16_t page = spm::page_bytes;
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constexpr std::uint16_t eeprom_end = avr::hw::db.mem.eeprom_size - 1;
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// The config page (TSB's LASTPAGE), one page below the boot section: the
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// application's jump vector, then these.
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consteval std::uint16_t config_page(std::uint16_t boot_bytes)
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{
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return spm::flash_bytes - boot_bytes - page;
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}
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constexpr std::uint8_t timeout_at = 2;
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constexpr std::uint8_t password_at = 3;
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// The firmware version stamp, in the encoding the host decodes.
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consteval std::uint16_t date_stamp(std::uint16_t year, std::uint16_t month, std::uint16_t day)
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{
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return year * 512 + month * 32 + day;
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}
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// BUILDSTATE F3: the native-UART fixed-baud lineage.
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constexpr std::uint8_t build_state = 0xF3;
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constexpr std::uint8_t atmega_marker = 0xAA;
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consteval auto info_block(std::uint16_t build_date, std::uint16_t app_end)
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{
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const auto low = [](std::uint16_t word) { return static_cast<std::uint8_t>(word); };
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const auto high = [](std::uint16_t word) { return static_cast<std::uint8_t>(word >> 8); };
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const std::uint16_t app_end_words = app_end / 2;
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return std::to_array<std::uint8_t>({
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'T',
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'S',
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'B',
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low(build_date),
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high(build_date),
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build_state,
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avr::hw::db.signature[0],
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avr::hw::db.signature[1],
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avr::hw::db.signature[2],
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page / 2,
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low(app_end_words),
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high(app_end_words),
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low(eeprom_end),
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high(eeprom_end),
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atmega_marker,
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atmega_marker,
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});
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}
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inline const std::uint8_t *flash_ptr(std::uint16_t addr)
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{
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return reinterpret_cast<const std::uint8_t *>(addr);
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}
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} // namespace tsb
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