New-Tech Europe | February 2019

the availability of RAM, flash, pins and peripherals, which is what we expect when selecting a microcontroller. For developers that are looking to get started with Armv8-M, there are two development kits to choose from. The Microchip SAML10 Xplained evaluation board includes the SAM L10E14A microcontroller which includes 16 Kbytes of flash, 2 Kbytes of data flash memory, 4 Kbytes SRAM, and comes in a 32- pin package. The Microchip SAML11 Xplained Evaluation Board includes the SAM L11E16A microcontroller which includes 64 Kbytes of flash, 2 Kbytes of data flash memory, 16 Kbytes SRAM and also comes in a 32-pin package. The development boards are identical minus the fact that the processors are different. The Xplained board can be seen in Figure 4. How TrustZone applications work Developers working with TrustZone will discover that the way in which an embedded application is developed is going to dramatically change. First, developers need to separate out their applications spaces to determine what code and libraries belong in the secure state and which belong in the non-secure state. Once this is determined, a developer creates two different software applications; one for the secure code and one for the non-secure code. This can be done very easily using a compiler/IDE like Keil MDK. What a developer essentially ends up with is a multi-project workspace where one project is the secure code and the other is the non-secure code (Figure 5). When a TrustZone application starts, the code begins executing in the secure state. This allows a developer to immediately establish a root of trust from which the rest of the application can execute. Once

Figure 3: The Microchip SAML10 and SAML11 microcontroller variants. Only the SAML11 parts include Arm TrustZone. (Image source: Microchip Technology)

Microchip has produced two main versions of the Armv8-M architecture in their SAML10 and SAML11 family of parts. The SAML10 version does NOT include TrustZone, while the SAML11 parts do. Figure 3 shows all the variants for the SAML10 and SAML11 parts that are currently in production and available. The main differences between the variants is

has parts in production is Microchip Technology. There have been announcements from other processor manufacturers such as Nuvoton that parts are coming. We can expect over the next 12 months to see a dramatic increase in the number of Armv8-M parts, including those that support TrustZone.

Figure 4: The Microchip SAML10/L11 development board is based on the Armv8 architecture. The SAML11 version supports TrustZone (Image source: Keil)

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