In the tfm_secure_boot.rst's "Executing firmware upgrade on Musca-B1 board" section, the signed tfm binary names in the example commands don't match with the related file names in the actual build output. They're either "tfm_sig0.bin" and "tfm_sig1.bin" (in the install/outputs{TARGET_NAME} directory) or "tfm_s_ns_signed_0" and "tfm_s_ns_signed_1" (in the fvp directory).