The host processor is the intelligent part of the protocol: it chooses the image sector to download, reads back the downloaded image area sector to verify the written image was written correctly, and authorizes the use of the image, etc. If the image in the downloaded image area is valid, the boot loader jumps to the valid image area. If the image in the downloaded image area is not a valid image, the serial boot loader starts in serial boot loading mode and waits for commands from host processor (the PC in our case).
This decision is made based on the validity of the downloaded image.
Upon power cycle, a decision is made in the SBL whether to start serial boot loading or to jump to the downloaded image area. The SBL code resides at the bottom of the flash memory in the CC254x, as shown below. This demo consists of a CC254x target image which is compiledas an SBL-enabled configuration, a CC254x programmed with the SBL, and the CC254X_SBL_Tool which will function as the host. Serial bootloading is a feature that enables a cc254x device to load into flash an embedded software image from a host processor through a serial interface such as UART or SPI. Note that there is also an example SBL-configured project included with the 1.4.0 stack release - HostTestRelease. This document will also describe how to use an encrypted version of the SBL - the EBL or encrypted bootloader. This example explains the Serial Bootloader (SBL) and provides a step-by-step procedure of how to compile a project for the SBL and load it into the CC254x's flash. Other Parts Discussed in Thread: CC2541,, AES-128 Serial Bootloading
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