# Target of this port

This port adds the support that FreeRTOS applications can call the secure
services in Trusted Firmware M(TF-M) through Platform Security Architecture
(PSA) API based on the ARM Cortex-M33 platform.

The Platform Security Architecture (PSA) makes it quicker, easier and cheaper
to design security into a device from the ground up. PSA is made up of four key
stages: analyze, architect, implement, and certify. See [PSA Resource Page](https://developer.arm.com/architectures/security-architectures/platform-security-architecture).

TF-M is an open source project. It provides a reference implementation of PSA
for Arm M-profile architecture. Please get the details from this [link](https://git.trustedfirmware.org/TF-M/trusted-firmware-m.git/about/).

# Derivation of the source code

* ```os_wrapper_freertos.c```
  The implementation of APIs which are defined in ```os_wrapper\mutex.h``` by TF-M
  (tag: TF-Mv1.1). The implementation is based on FreeRTOS mutex type semaphore.

# Usage notes

To build a project based on this port:
* Step 1: build the secure image. Please follow the **Build the Secure Side** section for details.
* Step 2: build the nonsecure image. Please follow the **Build the Non-Secure Side** for details.

## Build the Secure Side

### Get the TF-M source code

See the [link](https://git.trustedfirmware.org/TF-M/trusted-firmware-m.git/) to get the source code. This port is based on TF-M version **tag: TF-Mv1.1**.

### Build TF-M

Please refer to this [link](https://git.trustedfirmware.org/TF-M/trusted-firmware-m.git/tree/docs/getting_started/tfm_build_instruction.rst) to build the secure side.
_**Note:** ```CONFIG_TFM_ENABLE_CTX_MGMT``` must be configured as "OFF" when building TF-M_.

## Build the Non-Secure Side

Please copy all the files in ```freertos_kernel\portable\GCC\ARM_CM33_NTZ``` into the ```freertos_kernel\portable\GCC\ARM_CM33_TFM``` folder before using this port. Note that TrustZone is enabled in this port. The TF-M runs in the Secure Side.

Please call the API ```tfm_ns_interface_init()``` which is defined in ```os_wrapper_freertos.c``` at the very beginning of your application. Otherwise, it will always fail when calling a TF-M service in the Nonsecure Side.

### Configuration in FreeRTOS kernel

* ```configRUN_FREERTOS_SECURE_ONLY```
This macro should be configured as 0. In this port, TF-M runs in the Secure Side while FreeRTOS
Kernel runs in the Non-Secure Side.

* ```configENABLE_FPU```
The setting of this macro is decided by the setting in Secure Side which is platform-specific.
If the Secure Side enables Non-Secure access to FPU, then this macro can be configured as 0 or 1. Otherwise, this macro can only be configured as 0.

* ```configENABLE_TRUSTZONE```
This macro should be configured as 0 because TF-M doesn't use the secure context management function of FreeRTOS. New secure context management might be introduced when TF-M supports multiple secure context.


### Integrate TF-M Non-Secure interface with FreeRTOS project

To enable calling TF-M services by the Non-Secure Side, the files below should be included in the FreeRTOS project and built together.
* files in ```trusted-firmware-m\build\install\export\tfm\src```
  These files contain the implementation of PSA Functional Developer APIs which can be called by Non-Secure Side directly and PSA Firmware Framework APIs in the IPC model. These files should be taken
  as part of the Non-Secure source code.
* files in ```trusted-firmware-m\build\install\export\tfm\include```
  These files are the necessary header files to call TF-M services.
* ```trusted-firmware-m\build\install\export\tfm\veneers\s_veneers.o```
  This object file contains all the Non-Secure callable functions exported by
  TF-M and it should be linked when generating the Non-Secure image.



*Copyright (c) 2020, Arm Limited. All rights reserved.*
