feat: riscv-virt-rt 0.1.0 — board support for QEMU's RISC-V virt machine (#219)

* feat: riscv-virt-rt 0.1.0 — board support for QEMU's RISC-V virt machine

The first bare-metal package in this index. With it, a firmware project is an
ordinary mcpp project:

    mcpp add riscv-virt-rt@0.1.0
    mcpp build --target riscv64-none-elf     # + .bin, .map, a size summary
    mcpp run   --target riscv64-none-elf     # boots in qemu
    mcpp test  --target riscv64-none-elf

and its manifest names no linker script, load address, libc, -nostdlib or
emulator — there is no [target.*] section at all. Verified end to end against
this tree as a path index: added, downloaded, built and booted, printing from
the firmware.

Two descriptor choices are load-bearing, both measured rather than assumed:

* Form A (`mcpp = "*/mcpp.toml"`), because the package ships a build.mcpp and
  mcpp looks for that at the package ROOT. Form B leaves the root at the
  extract dir and absorbs the tarball's wrap layer inside each source glob,
  which would leave build.mcpp one level down and unfound — the package would
  resolve and compile, then link against nothing.

* `deps` at the xpm PLATFORM level, carrying xim:picolibc-riscv and
  xim:qemu-riscv. mcpp materializes `[xlings] deps` for the ROOT project only,
  so the package's own declaration does not reach a consumer. Verified by
  removing picolibc from the store: `mcpp add` + `mcpp build` reinstalled it
  and linked; without this edge the build stops at build.mcpp saying the
  sysroot is declared but not installed.

Requires mcpp >= 2026.8.19.2 (build.mcpp calls `mcpp::runner`). No workspace
member under tests/examples/: those run on all three platforms with no
capability gate, and this one needs an emulator and a target sysroot. The
package's own repo CI installs both and boots rv64 and rv32 on every push.

* riscv-virt-rt 0.2.0 — the version that ships the project template

0.2.0 adds templates/blinky, so `mcpp new <name> --template riscv-virt-rt`
produces a firmware project that builds, boots and tests unmodified. The
template ships with the package rather than with mcpp, whose builtin registry
is frozen at `bin`; `mcpp new` writes the dependency line at the version it
resolved, so the two cannot drift.

0.1.0 stays listed: a version that has been published is a version someone may
have pinned.

---------

Co-authored-by: speak-agent <x.d2learn.org@gmail.com>

Author: Sunrisepeak

pkgs/r/riscv-virt-rt.lua

@@ -0,0 +1,87 @@
+-- riscv-virt-rt — board support for QEMU's RISC-V `virt` machine.
+--
+-- Form A (`mcpp = "*/mcpp.toml"`) rather than an inline Form B table, and the
+-- choice is load-bearing rather than stylistic: this package ships a
+-- `build.mcpp`, and mcpp looks for that at the PACKAGE ROOT. Form B leaves the
+-- root at the extract dir and absorbs the tarball's `riscv-virt-rt-<v>/` wrap
+-- layer inside each source glob — which would leave `build.mcpp` one level
+-- down, unfound, and the package would resolve, compile its module, and then
+-- link against nothing. Pointing at the manifest moves the root inside the
+-- wrap layer, where both the manifest and the program live.
+--
+-- ⚠️ `deps` is at the xpm PLATFORM level, not in the mcpp segment. The two
+-- entries are xim packages (an emulator and a target sysroot), not mcpp
+-- packages, so they travel on xim's install-time dependency edge. This matters
+-- more than it looks: mcpp materializes `[xlings] deps` for the ROOT project
+-- only, so a consumer that just runs `mcpp add riscv-virt-rt` would otherwise
+-- get the board package with neither a libc nor an emulator, and find out at
+-- build.mcpp time.
+package = {
+    spec        = "1",
+    namespace   = "mcpplibs",
+    name        = "riscv-virt-rt",
+    description = "Board support for QEMU's RISC-V virt machine — picolibc, startup, memory layout and the emulator",
+    licenses    = {"Apache-2.0"},
+    repo        = "https://github.com/mcpplibs/riscv-virt-rt",
+    type        = "package",
+
+    -- 0.2.0 adds the project template (`mcpp new <name> --template
+    -- riscv-virt-rt`); 0.1.0 stays listed because a version that has been
+    -- published is a version someone may have pinned.
+    xpm = {
+        linux = {
+            deps = { "xim:picolibc-riscv@1.8.12", "xim:qemu-riscv@9.2.4-1" },
+            ["0.1.0"] = {
+                url    = {
+                    GLOBAL = "https://github.com/mcpplibs/riscv-virt-rt/archive/refs/tags/0.1.0.tar.gz",
+                    CN     = "https://gitcode.com/mcpp-res/riscv-virt-rt/releases/download/0.1.0/riscv-virt-rt-0.1.0.tar.gz",
+                },
+                sha256 = "8afb5ff2e9593b59f1f90029f57d577df454c78cdeff80760894c72aac7e5168",
+            },
+            ["0.2.0"] = {
+                url    = {
+                    GLOBAL = "https://github.com/mcpplibs/riscv-virt-rt/archive/refs/tags/0.2.0.tar.gz",
+                    CN     = "https://gitcode.com/mcpp-res/riscv-virt-rt/releases/download/0.2.0/riscv-virt-rt-0.2.0.tar.gz",
+                },
+                sha256 = "79f1dc4415a59ba828048eb8706322957723f8a6fd84bde3faba6a377e48242b",
+            },
+        },
+        macosx = {
+            deps = { "xim:picolibc-riscv@1.8.12", "xim:qemu-riscv@9.2.4-1" },
+            ["0.1.0"] = {
+                url    = {
+                    GLOBAL = "https://github.com/mcpplibs/riscv-virt-rt/archive/refs/tags/0.1.0.tar.gz",
+                    CN     = "https://gitcode.com/mcpp-res/riscv-virt-rt/releases/download/0.1.0/riscv-virt-rt-0.1.0.tar.gz",
+                },
+                sha256 = "8afb5ff2e9593b59f1f90029f57d577df454c78cdeff80760894c72aac7e5168",
+            },
+            ["0.2.0"] = {
+                url    = {
+                    GLOBAL = "https://github.com/mcpplibs/riscv-virt-rt/archive/refs/tags/0.2.0.tar.gz",
+                    CN     = "https://gitcode.com/mcpp-res/riscv-virt-rt/releases/download/0.2.0/riscv-virt-rt-0.2.0.tar.gz",
+                },
+                sha256 = "79f1dc4415a59ba828048eb8706322957723f8a6fd84bde3faba6a377e48242b",
+            },
+        },
+        windows = {
+            deps = { "xim:picolibc-riscv@1.8.12", "xim:qemu-riscv@9.2.4-1" },
+            ["0.1.0"] = {
+                url    = {
+                    GLOBAL = "https://github.com/mcpplibs/riscv-virt-rt/archive/refs/tags/0.1.0.tar.gz",
+                    CN     = "https://gitcode.com/mcpp-res/riscv-virt-rt/releases/download/0.1.0/riscv-virt-rt-0.1.0.tar.gz",
+                },
+                sha256 = "8afb5ff2e9593b59f1f90029f57d577df454c78cdeff80760894c72aac7e5168",
+            },
+            ["0.2.0"] = {
+                url    = {
+                    GLOBAL = "https://github.com/mcpplibs/riscv-virt-rt/archive/refs/tags/0.2.0.tar.gz",
+                    CN     = "https://gitcode.com/mcpp-res/riscv-virt-rt/releases/download/0.2.0/riscv-virt-rt-0.2.0.tar.gz",
+                },
+                sha256 = "79f1dc4415a59ba828048eb8706322957723f8a6fd84bde3faba6a377e48242b",
+            },
+        },
+    },
+
+    -- The package's own manifest, inside the tarball's wrap directory.
+    mcpp = "*/mcpp.toml",
+}