Bootloader Functionality - Texas Instruments SimpleLink CC2620 Technical Reference Manual

Bootloader Functionality

8.1 Bootloader Functionality
The CC26xx and CC13xx devices include a simple, ROM-based bootloader that can communicate with an
external device over the serial interfaces on the UART0 and SSI0 peripherals. The same communication
protocol is used on both serial interfaces. These peripherals are IPs from ARM.
The main purpose of the ROM bootloader is to support functionality for downloading a flash image.
8.1.1 Bootloader Disabling
The ROM bootloader supports commands that can read the flash image. Due to this read capability, a
secure measure for disabling the bootloader has been implemented. If the bootloader is disabled using the
CCFG BOOTLOADER_ENABLE parameter, the bootloader is unable to execute any commands, which
prevents attackers from using the bootloader if the Cortex-M3 program counter (PC) is forced to execute
from the bootloader code.
8.1.2 Bootloader Backdoor
To enter the ROM bootloader even when a valid image is in the flash, a bootloader backdoor is
implemented. The CCFG parameter BL_ENABLE can enable this backdoor. The backdoor functionality
uses a configurable I/O pin (CCFG parameter BL_PIN_NO) and a configurable I/O pin level (CCFG
parameter BL_LEVEL).
If backdoor functionality is enabled, externally applying a configurable signal level on a configurable I/O
pin can force a ROM bootloader entry upon reset. If the backdoor is enabled and a valid flash image is
present, start-up code checks the level of the I/O pin. If the configured I/O-pin level matches the
configured signal level, the ROM bootloader does not transfer control to the flash image.
If the backdoor pin configuration matches one of the UART0 or SSI0 pins, the external user must deassert
the backdoor signal before transmitting on the UART0 or SSI0 interface.
Table 9-14 lists the BL_BACKDOOR_CONFIG parameter layout in CCFG.
8.2 Bootloader Interfaces
The bootloader communicates with an external device over a 2-pin UART or a 4-pin SSI interface. The
communication protocol and transport layers are described in the following sections.
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Bootloader
Copyright © 2015, Texas Instruments Incorporated
SWCU117C – February 2015 – Revised September 2015
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