docs/system: Document Musca boards

Provide a minimal documentation of the Musca boards.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20200507151819.28444-6-peter.maydell@linaro.org

MAINTAINERS

@@ -708,6 +708,7 @@ M: Peter Maydell <peter.maydell@linaro.org>
 L: qemu-arm@nongnu.org
 S: Maintained
 F: hw/arm/musca.c
+F: docs/system/arm/musca.rst
 
 Musicpal
 M: Jan Kiszka <jan.kiszka@web.de>

docs/system/arm/musca.rst

+Arm Musca boards (``musca-a``, ``musca-b1``)
+============================================
+
+The Arm Musca development boards are a reference implementation
+of a system using the SSE-200 Subsystem for Embedded. They are
+dual Cortex-M33 systems.
+
+QEMU provides models of the A and B1 variants of this board.
+
+Unimplemented devices:
+
+- SPI
+- |I2C|
+- |I2S|
+- PWM
+- QSPI
+- Timer
+- SCC
+- GPIO
+- eFlash
+- MHU
+- PVT
+- SDIO
+- CryptoCell
+
+Note that (like the real hardware) the Musca-A machine is
+asymmetric: CPU 0 does not have the FPU or DSP extensions,
+but CPU 1 does. Also like the real hardware, the memory maps
+for the A and B1 variants differ significantly, so guest
+software must be built for the right variant.
+

docs/system/target-arm.rst

@@ -77,6 +77,7 @@ undocumented; you can get a complete list by running
 
    arm/integratorcp
    arm/mps2
+   arm/musca
    arm/realview
    arm/versatile
    arm/vexpress