--- title: Device Mode vs Gateway Mode description: Device Mode vs Gateway Mode, SDK Modes --- [Skip to content](https://portal.sandgrain.eu/knowledge-base/device-mode-vs-gateway-mode#main-content) English Show submenu for translations ![SandGrain\_Logo\_RGB\_white-bijgesneden (1)](https://portal.sandgrain.eu/hs-fs/hubfs/SandGrain_Logo_RGB_white-bijgesneden%20(1).png?width=427&height=83&name=SandGrain_Logo_RGB_white-bijgesneden%20(1).png) Open main navigation Close main navigation - English Show submenu for translations - [Contact us](https://portal.sandgrain.eu/login) [Contact us](https://portal.sandgrain.eu/login?hsLang=en) How can we help you? - There are no suggestions because the search field is empty. 1. [Knowledge Base](https://portal.sandgrain.eu/knowledge-base?hsLang=en) 2. [SDK](https://portal.sandgrain.eu/knowledge-base/sdk?hsLang=en) 3. [SandGrain SDK](https://portal.sandgrain.eu/knowledge-base/sdk?hsLang=en#sandgrain-sdk) October 6, 2026 # Device Mode vs Gateway Mode **Who this is for:** Developers who need to understand what they're actually building and running. This shapes every walkthrough. **What you'll accomplish:** Know the difference between the two SDK modes, when to use each, and what functions each one includes. ### One codebase, two builds The SandGrain SDK is a single portable C codebase. A **compile-time** parameter, `SDK_MODE`, selects which functions and port implementations are compiled into a given binary: - **`DEVICE_MODE`** builds `test_device`, runs on the unit that holds the SandGrain Token. - **`GATEWAY_MODE`** builds `test_gw`, runs on the relay/orchestrator node. There's also a **Cloud SDK agent** written in Python, which provides the cloud-side counterpart. If `SDK_MODE` is not defined, the SDK deliberately fails to compile with an error. ### What each mode does | | Device mode (`test_device`) | Gateway mode (`test_gw`) | | --- | --- | --- | | **Runs on** | The unit holding the Token | The relay / orchestrator node | | **Crypto Token** | **Always required** (USB/SPI) | Optional (`GW_CRYPTO_ENABLED`) | | **Key functions** | `SGR_SDK_Initialize`, `SGR_SDK_Authenticate_Via_GW`, `SGR_SDK_Verification_FW`, `SGR_SDK_Installation` | `SGR_SDK_Initialize`, `SGR_SDK_Authentication_Token_To_Server`, `SGR_SDK_Authentication_Server_To_Token`, `SGR_SDK_GW_Run` | | **Extra startup work** | Initializes the middleware | Also initializes the authentication database and registers all whitelisted devices | ### When to use which - Use **`DEVICE_MODE`** on the unit that physically holds the SandGrain chip. - Use **`GATEWAY_MODE`** on the relay/orchestrator node that sits between devices and the cloud. - `SGR_SDK_GW_Run` is the recommended entry point for the Gateway application loop, it polls all device channels and routes each request to the right handler. #### Good to know - Both modes **build the same way** (`make`) and run on the same set of operating systems. - Only the device node strictly needs the USB/SPI Token attached. - `GW_CRYPTO_ENABLED` has **no effect in `DEVICE_MODE`**, the Token is always required there. ### Maintenance note The `sdk_fw/` core directory should **not** be modified, with one exception: `src/services/database/auth_db_whitelist.c` (the device whitelist). After pulling new device-side code, rebuild the firmware with `make clean && make`. ### Bluetooth LE variant There is a Bluetooth LE build of the Gateway, used when the devices are Nordic boards rather than USB Tokens. In that variant the Gateway runs as the **BLE central**: it scans for boards advertising as `SandGrain-Dev`, serves one board per channel, and is built with `make GW_BLE=1 GW_BLE_DEVICES=` (default 2 channels). The device SDK, meanwhile, is flashed onto the Nordic board rather than compiled on a PC. The gateway-to-cloud MQTT path and the TrustBridge stack are unchanged. See [*Nordic nRF54L15 Boards over Bluetooth LE*](https://portal.sandgrain.eu/knowledge-base/what-question-is-your-article-answeringwalkthrough-nordic-nrf54l15-boards-over-bluetooth-le?hsLang=en). ### Single-board (cellular) variant The cellular variant collapses both roles onto one board. A Nordic nRF9151-DK is built with `SDK_MODE=GATEWAY_MODE` and `GW_CRYPTO_ENABLED=1`, wires its own SGT1001 chip over SPI, and authenticates its own token against the cloud over LTE (the Token-to-Server / Server-to-Token path). This is a development shortcut: there's no separate device node, and the board is both the thing being proven and the thing doing the proving. Production keeps device and gateway separate. See [*Nordic nRF9151-DK over LTE / Cellular*](https://portal.sandgrain.eu/knowledge-base/walkthrough-nordic-nrf9151-dk-over-lte-/-cellular?hsLang=en). | [Access & Credentials](https://portal.sandgrain.eu/knowledge-base/access-credentials-your-cyberrock-access-package?hsLang=en) | [Choosing Your Setup Path](https://portal.sandgrain.eu/knowledge-base/choosing-your-setup-path?hsLang=en) | | --- | --- |   - [User Documentation](https://portal.sandgrain.eu/knowledge-base/user-documentation?hsLang=en#main-content) - [Quick Starter Guide](https://portal.sandgrain.eu/knowledge-base/user-documentation?hsLang=en#quick-starter-guide) - [User Manual](https://portal.sandgrain.eu/knowledge-base/user-documentation?hsLang=en#user-manual) - [Whitepaper](https://portal.sandgrain.eu/knowledge-base/user-documentation?hsLang=en#whitepaper) - [Token Leaflet](https://portal.sandgrain.eu/knowledge-base/user-documentation?hsLang=en#token-leaflet) - [Claim Token Procedure](https://portal.sandgrain.eu/knowledge-base/user-documentation?hsLang=en#claim-token-procedure) - [Daisy Chain](https://portal.sandgrain.eu/knowledge-base/user-documentation?hsLang=en#daisy-chain) - [Release Note](https://portal.sandgrain.eu/knowledge-base/user-documentation?hsLang=en#release-note) - [Naming Convention](https://portal.sandgrain.eu/knowledge-base/user-documentation?hsLang=en#naming-convention) - [SandGrain SDK](https://portal.sandgrain.eu/knowledge-base/user-documentation?hsLang=en#sandgrain-sdk) - [TrustBridge](https://portal.sandgrain.eu/knowledge-base/user-documentation?hsLang=en#trustbridge) - [API Documentation](https://portal.sandgrain.eu/knowledge-base/api-documentation?hsLang=en#main-content) - [Device API Integration](https://portal.sandgrain.eu/knowledge-base/api-documentation?hsLang=en#device-api-integration) - [Daisy Chain and Attestation](https://portal.sandgrain.eu/knowledge-base/api-documentation?hsLang=en#daisy-chain-and-attestation) - [SDK](https://portal.sandgrain.eu/knowledge-base/sdk?hsLang=en#main-content) - [Core Functions](https://portal.sandgrain.eu/knowledge-base/sdk?hsLang=en#core-functions) - [SandGrain SDK](https://portal.sandgrain.eu/knowledge-base/sdk?hsLang=en#sandgrain-sdk) [![SandGrain\_Logo\_RGB\_white-bijgesneden (1)-1](https://portal.sandgrain.eu/hs-fs/hubfs/SandGrain_Logo_RGB_white-bijgesneden%20(1)-1.png?width=427&height=83&name=SandGrain_Logo_RGB_white-bijgesneden%20(1)-1.png "SandGrain_Logo_RGB_white-bijgesneden (1)-1")](https://portal.sandgrain.eu/?hsLang=en) [mailto:email@email.com](mailto:email@email.com) Copyright © 2026, sandgrain.eu