4 Conclusion

This application note documents the RBL boot flow and the typical SBL boot flow. The user can implement their SBL as per the suggestions and recommendations mentioned in the document. The RBL always require a signed image to work with. In context of the RBL, every image received is referred to as the SBL. In functional mode the RBL reads from the SDF at zero offset and expects a SBL to already be present at that offset. In flashing mode, RBL loads the flash writer image onto the RAM over UART and begins execution. For RBL this image can also be signed and the RBL treats this image as the SBL as well. Thus, in both the modes the RBL loads a valid image (for the SBL) onto the RAM memory of the R5F or the main sub system. The max size of the SBL or the flash writer or any other image that is loaded on the RAM memory can be 960 KB along with the attached certificate. TI also handles these various images as SBL. Hence the example flash writer image is referred as “sbl_uart_uniflash” in the MCU plus SDK package which simply downloads images onto the serial flash. These downloaded images can be another SBL and application images. Thus, in functional mode where the RBL loads a valid image form the sFLASH, RBL loads the SBL downloaded earlier. This SBL can then perform all the necessary functions as described in section 4.4 and then load the application images onto the respective cores.