rttsh

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rttsh is a command-line terminal over SEGGER J-Link RTT for automated on-board firmware verification. The firmware exposes a command console through SEGGER RTT; on the host side, Lua scripts send commands, match responses, and assert on output and timing, so on-board verification can run in batches and be wired into CI. Communication and flashing share the same debug probe and do not occupy target peripherals such as UART.

An MCP server (rttsh mcp) and the skills/rttsh-verify-on-board skill are provided for AI coding agents.

Requirements

Windows (depends on JLink_x64.dll); the .NET 10 runtime (needed by the framework-dependent installer, bundled in the self-contained package); the SEGGER J-Link driver and a probe (the J-Link DLL is auto-detected, or point to one with --dll); firmware linked with the RTT control block (_SEGGER_RTT) and already flashed to the target board. See installer/ for installers and building from source.

Usage

--chip must match a name from the J-Link device database (case-insensitive); look it up with rttsh list-devices --filter H743. An invalid name fails fast with an error (exit 2) and never opens the device-selection dialog.

Send one line and wait for the response:

rttsh send "led r on" --chip STM32H743XI --wait 300

--hex sends raw bytes. Running without a subcommand opens an interactive terminal (-tui selects the chat-style layout), Ctrl+C to exit; when output is redirected it switches to receive-only mode, so it can be piped through grep and the like.

Script mode is the core of automated verification. script --eval runs Lua inline:

rttsh script --eval 'rtt.send("led r toggle"); rtt.expect("LED r toggled", 500)' --chip STM32H743XI

Systematic test cases are written as script files. rtt.expect returns the matched text, the match itself, and the pattern's captures as extra values, so response fields are captured in one step:

-- Tests/t21_led_query.lua
local function query_led(name)
  rtt.send("led "..name)
  local t, m, state = rtt.expect("LED "..name.." (%a+)", 500)
  return state
end
local g0 = query_led("g")
rtt.send("led g toggle")
rtt.expect("LED g toggled", 500)
assert(query_led("g") ~= g0, "state did not flip")
rtt.log("t21 PASS")

The full suite lives in examples/stm32/Tests (23 scripts, a real target board required), covering field extraction, negative assertions, timing windows, channel independence, and more.

An expect timeout is a failure (exit 1), and the error message includes the tail of the receive buffer so the firmware's actual response is visible right in the failure. The expect family covers the common shapes: rtt.try_expect returns nil, msg on a quiet window instead of raising (polling loops), rtt.expect_absent is a first-class negative assertion, rtt.expect_any waits for whichever of several patterns matches first, rtt.read_line consumes one newline-terminated line (nil on timeout), and rtt.flush discards stale output. The rtt.* API also covers binary transfer and target memory access (rtt.mem_read/rtt.mem_write; rtt.mem_read(addr) reads one 32-bit unit as a scalar).

By default the RTT control-block address is found by scanning RAM from the SDK; --elf <image> resolves it from the _SEGGER_RTT symbol instead, following rebuilds automatically.