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The mps2_an521 board configuration is used by Zephyr applications that run on the MPS2+ AN521 board. It provides support for the MPS2+ AN521 ARM Cortex-M33 CPU and the following devices:

  • Nested Vectored Interrupt Controller (NVIC)

  • System Tick System Clock (SYSTICK)

  • Cortex-M System Design Kit GPIO

  • Cortex-M System Design Kit UART


In addition to enabling actual hardware usage, this board configuration can also use QEMU to emulate the AN521 platform running on the MPS2+.

More information about the board can be found at the MPS2 FPGA Website.


This board configuration makes no claims about its suitability for use with actual MPS2 hardware systems using AN521, or any other hardware system. It has been tested on actual hardware, but its primary purpose is for use with QEMU and unit tests for the ARM Cortex-M33.

Zephyr board options

The MPS2+ AN521 is a dual core SoC with Cortex-M33 architecture on both cores (CPU0 and CPU1). Zephyr provides support for building firmware images for both CPU0 and CPU1. For CPU0 supporting ARM Security Extensions both Secure and Non-Secure firmware images may be built.

The BOARD options are summarized below:




For building Secure (or Secure-only) firmware on CPU0


For building Non-Secure firmware for CPU0


For building firmware on CPU1

Memory Partitioning

The AN521 has 4MB allocated for code space, and 4MB for SRAM. These memory regions are shared across both cores, and are aliased in both secure and non-secure regions, where the secure memory alias has an offset of 0x10000000 relative to non-secure.

The following memory map and partitioning schemes are used by default, where the offset value is the offset from the base of the 4MB code or SRAM block, ignoring the S/NS alias difference.



Code (Offset)

SRAM (Offset)

S/NS Alias



4MB (0)

4MB (0)




512KB (1MB)

512KB (1MB)




468KB (3628KB)

512KB (1.5MB)


The mps2_an521_ns board target is intended to be used with TF-M, with the Zephyr memory map matching the AN521 memory map defined upstream in TF-M. TF-M boots the secure processing environment before initialising Zephyr in the non-secure processing environment. The non-secure Zephyr image is offset to make room for the secure bootloader, and the secure firmware (TF-M), resulting in a starting address of 0x00100000. SRAM begins with a 1MB offset at 0x28100000.

The mps2_an521_remote board target is setup for the second core on the AN521, using the final 468KB code memory in the 4MB code block. This value is chosen to maintain compatibility with TF-M, which marks that final 468KB code region as Unused. Code memory thus starts with an offset of 3628KB (address 0x0038B000), and sram starts with an offset of 1.5MB (address 0x28180000).

This memory map enables the two alternative board targets to be used together if required, at the cost of reducing the amount of code memory available on the second core to the worst-case scenario from TF-M.

When using one of the alternative board targets (mps2_an521_ns or mps2_an521_remote), care needs to be taken with the amount of code or SRAM memory used on the primary board target (mps2_an521) since there is some overlap in the memory maps.


ARM MPS2+ AN521 provides the following hardware components:

  • Dual core ARM Cortex-M33

  • Soft Macro Model (SMM) implementation of SSE-200 subsystem

  • Memory

    • 4MB of code memory (SSRAM1)

    • 4MB of SRAM (SSRAM2 and SSRAM3)

    • 16MB of parallel SRAM (PSRAM, non-secure only)

    • 8KB of NVM code

  • Debug

    • P-JTAG, SWD & 16-bit TRACE

    • UART port

  • Interface

    • AHB GPIO connected to the EXP port

    • UART

    • SPI

    • I2C

    • I2S

    • Color LCD serial interface

    • Ethernet

    • VGA

  • On-board Peripherals

    • Color LCD

    • 8 LEDs

    • 8 Switches

    • External SSRAM1, SSRAM2 & SSRAM3

    • SMSC9220

    • CS42L52

User push buttons

The mps2_an521 board provides the following user push buttons:

  • ON power on

  • nSRST: Cortex-M33 system reset and CoreSight debug reset

  • USERPB0 and USERPB1: User defined buttons

Supported Features

The mps2_an521 board configuration supports the following hardware features:






nested vector interrupt controller






serial port-polling; serial port-interrupt













Other hardware features are not currently supported by the port. See the MPS2 FPGA Website for a complete list of MPS2+ AN521 board hardware features.

The default configuration can be found in the defconfig file: boards/arm/mps2_an521/mps2_an521_defconfig.

Interrupt Controller

MPS2+ AN521 is a Cortex-M33 based SoC and has 15 fixed exceptions and 77 IRQs.

A Cortex-M33-based board uses vectored exceptions. This means each exception calls a handler directly from the vector table.

Zephyr provides handlers for exceptions 1-7, 11, 12, 14, and 15, as listed in the following table:




Used by Zephyr Kernel



system initialization



system fatal error


Hard fault

system fatal error



MPU fault

system fatal error



system fatal error


Usage fault

Undefined instruction, or switch attempt to ARM mode

system fatal error



Unauthorized access to secure region from ns space

system fatal error



not handled



not handled



not handled



system calls, kernel run-time exceptions, and IRQ offloading


Debug monitor

system fatal error



not handled



context switch



system clock



not handled



not handled



not handled

Pin Mapping

The ARM MPS2+ AN521 Board has 4 CMSDK AHB GPIO controllers. Each providing 16 bits of IO. These controllers are responsible for pin-muxing, input/output, pull-up, etc.

All GPIO controller pins are exposed via the following sequence of pin numbers:

  • Pins 0 - 15 are for GPIO0

  • Pins 16 - 31 are for GPIO1

  • Pins 32 - 47 are for GPIO2

  • Pins 48 - 51 are for GPIO3

Mapping from the ARM MPS2+ AN521 Board pins to GPIO controllers:

  • D0 : EXT_0

  • D1 : EXT_4

  • D2 : EXT_2

  • D3 : EXT_3

  • D4 : EXT_1

  • D5 : EXT_6

  • D6 : EXT_7

  • D7 : EXT_8

  • D8 : EXT_9

  • D9 : EXT_10

  • D10 : EXT_12

  • D11 : EXT_13

  • D12 : EXT_14

  • D13 : EXT_11

  • D14 : EXT_15

  • D15 : EXT_5

  • D16 : EXT_16

  • D17 : EXT_17

  • D18 : EXT_18

  • D19 : EXT_19

  • D20 : EXT_20

  • D21 : EXT_21

  • D22 : EXT_22

  • D23 : EXT_23

  • D24 : EXT_24

  • D25 : EXT_25

  • D26 : EXT_26

  • D27 : EXT_30

  • D28 : EXT_28

  • D29 : EXT_29

  • D30 : EXT_27

  • D31 : EXT_32

  • D32 : EXT_33

  • D33 : EXT_34

  • D34 : EXT_35

  • D35 : EXT_36

  • D36 : EXT_38

  • D37 : EXT_39

  • D38 : EXT_40

  • D39 : EXT_44

  • D40 : EXT_41

  • D41 : EXT_31

  • D42 : EXT_37

  • D43 : EXT_42

  • D44 : EXT_43

  • D45 : EXT_45

  • D46 : EXT_46

  • D47 : EXT_47

  • D48 : EXT_48

  • D49 : EXT_49

  • D50 : EXT_50

  • D51 : EXT_51

Peripheral Mapping:

  • UART_3_RX : D0

  • UART_3_TX : D1

  • SPI_3_CS : D10

  • SPI_3_MOSI : D11

  • SPI_3_MISO : D12

  • SPI_3_SCLK : D13

  • I2C_3_SDA : D14

  • I2C_3_SCL : D15

  • UART_4_RX : D26

  • UART_4_TX : D30

  • SPI_4_CS : D36

  • SPI_4_MOSI : D37

  • SPI_4_MISO : D38

  • SPI_4_SCK : D39

  • I2C_4_SDA : D40

  • I2C_4_SCL : D41

For mode details refer to MPS2+ AN521 Technical Reference Manual (TRM).


MPS2+ has 8 built-in LEDs connected to Serial Configuration Controller (SCC).


The SCC register CFG_REG1 Bits [7:0] for LEDa, 0 = OFF 1 = ON.

System Clock

MPS2+ AN521 has several clocks connected:

  • MAINCLK : 20MHz

  • SYSCLK : 20MHz

  • S32KCLK : 32kHz

  • TRACECLK : 20MHz

  • SWCLKTCK : 20MHz


Serial Port

The MPS2+ AN521 has five UARTs. The Zephyr console output by default, uses UART0, which is J10 on the board.

UART2 is reserved. And UART 1, 3 and 4 are alt-functions on the EXP ports.

Security components

  • Implementation Defined Attribution Unit (IDAU). The IDAU is used to define secure and non-secure memory maps. By default, all of the memory space is defined to be secure accessible only

  • Secure and Non-secure peripherals via the Peripheral Protection Controller (PPC). Peripherals can be assigned as secure or non-secure accessible

  • Secure boot

  • Secure AMBA® interconnect

Serial Configuration Controller (SCC)

The MPS2+ AN521 implements a Serial Configuration Control (SCC) register. The purpose of this register is to allow individual control of clocks, reset-signals and interrupts to peripherals, and pin-muxing, and the LEDs and switches.

Programming and Debugging

MPS2+ AN521 (CPU0) supports the Armv8m Security Extension. Applications built for the mps2_an521 board by default boot in the Secure state.

MPS2+ AN521 (CPU1) does not support the Armv8m Security Extension.

Building Secure/Non-Secure Zephyr applications with Arm® TrustZone®

Applications on the MPS2+ AN521 (CPU0) may contain a Secure and a Non-Secure firmware image. The Secure image can be built using either Zephyr or Trusted Firmware M (TF-M). Non-Secure firmware images are always built using Zephyr. The two alternatives are described below.


By default the Secure image for the MPS2+ AN521 (CPU0) is built using TF-M.

Building the Secure firmware with TF-M

The process to build the Secure firmware image using TF-M and the Non-Secure firmware image using Zephyr requires the following steps:

  1. Build the Non-Secure Zephyr application for MPS2+ AN521 (CPU0) using -DBOARD=mps2_an521_ns. To invoke the building of TF-M the Zephyr build system requires the Kconfig option BUILD_WITH_TFM to be enabled, which is done by default when building Zephyr as a Non-Secure application. The Zephyr build system will perform the following steps automatically:

    • Build the Non-Secure firmware image as a regular Zephyr application

    • Build a TF-M (secure) firmware image

    • Merge the output image binaries together

    • Optionally build a bootloader image (MCUboot)


Depending on the TF-M configuration, an application DTS overlay may be required, to adjust the Non-Secure image Flash and SRAM starting address and sizes.

Building the Secure firmware using Zephyr

The process to build the Secure and the Non-Secure firmware images using Zephyr requires the following steps:

  1. Build the Secure Zephyr application for MPS2+ AN521 (CPU0) using -DBOARD=mps2_an521 and CONFIG_TRUSTED_EXECUTION_SECURE=y and CONFIG_BUILD_WITH_TFM=n in the application project configuration file.

  2. Build the Non-Secure Zephyr application for MPS2+ AN521 (CPU0) using -DBOARD=mps2_an521_ns.

  3. Merge the two binaries together.

Building a Secure only application on MPS2+ AN521 (CPU0)

Build the Zephyr app in the usual way (see Building an Application and Run an Application), using -DBOARD=mps2_an521 for the firmware running on the MPS2+ AN521 (CPU0).

When building a Secure/Non-Secure application for the MPS2+ AN521 (CPU0), the Secure application will have to set the SAU/IDAU configuration to allow Non-Secure access to all CPU resources utilized by the Non-Secure application firmware. SAU/IDAU configuration shall take place before jumping to the Non-Secure application.

The following system components are required to be properly configured during the secure firmware:

  • AHB5 TrustZone Memory Protection Controller (MPC)

  • AHB5 TrustZone Peripheral Protection Controller (PPC)

  • Implementation-Defined Attribution Unit (IDAU)

For more details refer to Corelink SSE-200 Subsystem.

Building standalone applications on MPS2+ AN521 CPU1

Applications may be built for the second Cortex-M33 (remote) core of MPS2+ AN521. The core is referred to as CPU1.

Build the Zephyr app in the usual way (see Building an Application and Run an Application), using -DBOARD=mps2_an521_remote for the firmware running on the MPS2+ AN521 (CPU1).

The Zephyr build will automatically trigger building a minimal (empty) secure-only firmware for CPU0, which will be used to boot the remote core (CPU1).


MPS2+ AN521 provides:

  • A USB connection to the host computer, which exposes a Mass Storage

  • A Serial Port which is J10 on MPS2+ board

Build applications as described above. Here is an example for the Hello World application built as a secure-only application for CPU0.

# From the root of the zephyr repository
west build -b mps2_an521 samples/hello_world

Open a serial terminal (minicom, putty, etc.) with the following settings:

  • Speed: 115200

  • Data: 8 bits

  • Parity: None

  • Stop bits: 1

Reset the board, and you should see the following message on the corresponding serial port:

Hello World! mps2_an521

Uploading an application to MPS2+ AN521

Applications can be in elf, hex or bin format. The binaries are flashed when the board boots up, using files stored on the on-board Micro SD card. The Motherboard Configuration Controller (MCC) is responsible for loading the FPGA image and binaries.

Connect the MPS2+ to your host computer using the USB port. You should see a USB connection exposing a Mass Storage (V2M_MPS2 by default).

The update requires 3 steps:

  1. Copy application files to <MPS2 device name>/SOFTWARE/.

  2. Open <MPS2 device name>/MB/HBI0263C/AN521/images.txt.

  3. Update the AN521/images.txt file as follows:

TITLE: Versatile Express Images Configuration File

TOTALIMAGES: 1 ;Number of Images (Max: 32)

IMAGE0ADDRESS: 0x10000000 ;Please select the required executable program


Reset the board, and you should see the following message on the corresponding serial port:

Hello World! mps2_an521


Refer to the tfm_integration sample for more details about integrating with TF-M and multiple images scenario.