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.


ARM MPS2+ AN521 provides the following hardware components:

  • ARM Cortex-M33
  • Soft Macro Model (SMM) implementation of SSE-200 subsystem
  • Memory
    • 16MB internal memory SRAM
    • 8KB of NVM code
    • 224MB code memory
  • 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:

Interface Controller Driver/Component
NVIC on-chip nested vector interrupt controller
SYSTICK on-chip systick
UART on-chip serial port-polling; serial port-interrupt
PINMUX on-chip pinmux
GPIO on-chip gpio
WATCHDOG on-chip watchdog
TIMER on-chip timer

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:

Exc# Name Remarks Used by Zephyr Kernel
1 Reset   system initialization
2 NMI   system fatal error
3 Hard fault   system fatal error
4 MemManage MPU fault system fatal error
5 Bus   system fatal error
6 Usage fault Undefined instruction, or switch attempt to ARM mode system fatal error
7 SecureFault Unauthorized access to secure region from ns space system fatal error
8 Reserved   not handled
9 Reserved   not handled
10 Reserved   not handled
11 SVC   context switch and software interrupts
12 Debug monitor   system fatal error
13 Reserved   not handled
14 PendSV   context switch
15 SYSTICK   system clock
16 Reserved   not handled
17 Reserved   not handled
18 Reserved   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 please 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 supports the v8m security extension, and by default boots to the secure state.

When building a secure/non-secure application, the secure application will have to set the idau/sau and mpc configuration to permit access from the non-secure application before jumping.

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 please refer to Corelink SSE-200 Subsystem.


MPS2+ AN521 provides:

  • A USB connection to the host computer, which exposes a Mass Storage
  • A Serial Port which is J10 on MPS2+ board

Building a secure only application

You can build applications in the usual way. Here is an example for the Hello World application.

# 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

Building a secure/non-secure with Trusted Firmware

The process requires five steps:

  1. Build Trusted Firmware (tfm).
  2. Import it as a library to the Zephyr source folder.
  3. Build Zephyr with a non-secure configuration.
  4. Merge the two binaries together and sign them.
  5. Concatenate the bootloader with the signed image blob.

In order to build tfm please refer to Trusted Firmware M Guide. Follow the build steps for AN521 target while replacing the platform with -DTARGET_PLATFORM=AN521 and compiler (if required) with -DCOMPILER=GNUARM

Copy over tfm as a library to the Zephyr project source and create a shortcut for the secure veneers.

cp -r install/ $ZEPHYR_PROJECT/src/ext
cp $ZEPHYR_PROJECT/src/ext/install/export/tfm/veneers/s_veneers.o $ZEPHYR_PROJECT/src/ext

Build the Zephyr app in the usual way.

Uploading an application to MPS2+ AN521

Applications can be elf, hex or bin format. The binaries were flashed while the board boot up, all files were stored in the on-board Micro SD card in advance. The Motherboard Configuration Controller (MCC) will 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 needs 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