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Documentation/erbium: Add ET-Minion core diagram and references.

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Add the ET-Minion core diagram from the Erbium documentation
(aifoundry-org/erbium, Apache-2.0) and a short description of the
ET-Minion neighborhood, as suggested in review. Link the Erbium core,
interrupt, memory map and UART documentation and ET-platform, and note
that silicon uses a 10 MHz mtime while the emulator default is 2 MHz.

Signed-off-by: Afonso Oliveira <afonso.oliveira707@gmail.com>
This commit is contained in:
Afonso Oliveira 2026-09-23 17:41:39 +01:00 • committed by Xiang Xiao
parent cb53b267e5
commit a6cab8293d
2 changed files with 27 additions and 1 deletions
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Documentation/platforms/risc-v/erbium/boards/minion/index.rst
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@ -4,6 +4,19 @@ Erbium Minion
.. tags:: chip:erbium, arch:risc-v, vendor:aifoundry
.. figure:: erbium-minion-core.png
:align: center
:alt: ET-Minion core block diagram
ET-Minion core (source: `aifoundry-org/erbium
<https://github.com/aifoundry-org/erbium>`__, Apache-2.0).
The Erbium CPU subsystem is one ET-Neighborhood of eight dual-threaded
RV64IMFC ET-Minion cores (16 harts), derived from the Esperanto ET-SoC-1,
together with a PLIC, a CLINT-style machine timer and a shared instruction
cache. Erbium silicon is not yet available, so this board targets the
``erbium_emu`` system emulator. NuttX runs on hart 0.
Memory and interrupts
=====================
@ -15,7 +28,10 @@ stack. The linker checks that the image and idle stack fit in MRAM.
The PLIC at ``0xa0000000`` provides sources 1 through 6; UART0 uses source
3. Receive and transmit use interrupts, without periodic polling.
The machine timer uses ``mtime`` at ``0x80f40200`` and ``mtimecmp`` at
``0x80f40208``. Its default frequency is 2 MHz in the emulator.
``0x80f40208``. ``CONFIG_ERBIUM_MTIMER_FREQ`` defaults to 2 MHz, the
emulator's timer rate. The Erbium documentation specifies a 10 MHz
``mtime`` (one tick every 100 ns) on silicon, so set this option to match
the target.
Toolchain
=========
@ -138,3 +154,13 @@ for low-level console debugging.
The emulator reads host input into its finite RX FIFO immediately. Feeding
a long command through a pipe can overrun that FIFO. Automated console
tests should pace input, for example by waiting for each echoed character.
References
==========
* `Erbium documentation <https://erbium.readthedocs.io/en/latest/>`_
* `ET-Minion core <https://erbium.readthedocs.io/en/latest/minion/>`_
* `Interrupts and PLIC source IDs <https://erbium.readthedocs.io/en/latest/interrupts/>`_
* `CPU memory map <https://erbium.readthedocs.io/en/latest/cpu_mm/>`_
* `UART <https://erbium.readthedocs.io/en/latest/uart/>`_
* `ET-platform, including erbium_emu <https://github.com/aifoundry-org/et-platform>`_