docs: Add documentation for the mps3-an536 board

Add documentation for the mps3-an536 board type.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20240206132931.38376-14-peter.maydell@linaro.org

docs/system/arm/mps2.rst

@@ -1,7 +1,7 @@
-Arm MPS2 and MPS3 boards (``mps2-an385``, ``mps2-an386``, ``mps2-an500``, ``mps2-an505``, ``mps2-an511``, ``mps2-an521``, ``mps3-an524``, ``mps3-an547``)
-=========================================================================================================================================================
+Arm MPS2 and MPS3 boards (``mps2-an385``, ``mps2-an386``, ``mps2-an500``, ``mps2-an505``, ``mps2-an511``, ``mps2-an521``, ``mps3-an524``, ``mps3-an536``, ``mps3-an547``)
+=========================================================================================================================================================================
 
-These board models all use Arm M-profile CPUs.
+These board models use Arm M-profile or R-profile CPUs.
 
 The Arm MPS2, MPS2+ and MPS3 dev boards are FPGA based (the 2+ has a
 bigger FPGA but is otherwise the same as the 2; the 3 has a bigger
@@ -13,6 +13,8 @@ FPGA image.
 
 QEMU models the following FPGA images:
 
+FPGA images using M-profile CPUs:
+
 ``mps2-an385``
   Cortex-M3 as documented in Arm Application Note AN385
 ``mps2-an386``
@@ -30,6 +32,11 @@ QEMU models the following FPGA images:
 ``mps3-an547``
   Cortex-M55 on an MPS3, as documented in Arm Application Note AN547
 
+FPGA images using R-profile CPUs:
+
+``mps3-an536``
+  Dual Cortex-R52 on an MPS3, as documented in Arm Application Note AN536
+
 Differences between QEMU and real hardware:
 
 - AN385/AN386 remapping of low 16K of memory to either ZBT SSRAM1 or to
@@ -45,6 +52,30 @@ Differences between QEMU and real hardware:
   flash, but only as simple ROM, so attempting to rewrite the flash
   from the guest will fail
 - QEMU does not model the USB controller in MPS3 boards
+- AN536 does not support runtime control of CPU reset and halt via
+  the SCC CFG_REG0 register.
+- AN536 does not support enabling or disabling the flash and ATCM
+  interfaces via the SCC CFG_REG1 register.
+- AN536 does not support setting of the initial vector table
+  base address via the SCC CFG_REG6 and CFG_REG7 register config,
+  and does not provide a mechanism for specifying these values at
+  startup, so all guest images must be built to start from TCM
+  (i.e. to expect the interrupt vector base at 0 from reset).
+- AN536 defaults to only creating a single CPU; this is the equivalent
+  of the way the real FPGA image usually runs with the second Cortex-R52
+  held in halt via the initial SCC CFG_REG0 register setting. You can
+  create the second CPU with ``-smp 2``; both CPUs will then start
+  execution immediately on startup.
+
+Note that for the AN536 the first UART is accessible only by
+CPU0, and the second UART is accessible only by CPU1. The
+first UART accessible shared between both CPUs is the third
+UART. Guest software might therefore be built to use either
+the first UART or the third UART; if you don't see any output
+from the UART you are looking at, try one of the others.
+(Even if the AN536 machine is started with a single CPU and so
+no "CPU1-only UART", the UART numbering remains the same,
+with the third UART being the first of the shared ones.)
 
 Machine-specific options
 """"""""""""""""""""""""