USB secondary ISP bootloader for LPC11U68
Overview
A Secondary Bootloader (SBL) is a piece of code that allows a user application code to be downloaded using alternative channels other than the standard UART0 used by the internal bootloader (on chip). Possible secondary bootloaders can be written for USB, Ethernet, SPI, SSP, CAN, and even I/Os. The secondary bootloader utilizes IAP as a method to update the user’s application code.
The internal bootloader is the firmware that resides in the microcontroller’s boot ROM block and is executed on power-up and resets. After the boot ROM’s execution, the secondary bootloader would be executed, which will then execute the user application.
The purpose of this document is to use USB as an example for developing the secondary bootloader and the code was tested using the LPCXpresso 11U68 evaluation board.
The MSCD presents easy integration with a PC‘s operating systems. This class allows the embedded system’s flash memory space be represented as a folder in Windows/Linux. The user can update the flash with the binary image using drag and drop, so the following sections will present a guideline for development and implementation of the USB secondary bootloader design, configuration, and test.
USB secondary bootloader code is base on the USB Mass Storage Class demo. However in this application note, we do not attempt to explain how the Mass Storage Class is implemented.
Fig 1 LPCXpresso Board for LPC11U68
Setup file (sbl_config.h)
This file configures the secondary bootloader. The user should change this according to their application.
Some definitions and explanation:
MAX_USER_SECTOR – This parameter is device dependent. In a 256 KB device, it will be 29 sectors, however the size of the last 5 sectors become the 32 KB instead of the 4 KB, so in the application, MAX_USER_SECTOR chooses 23 (Fig 2).
CRP – Code Read Protection. This parameter allows select the desired CRP level. Choosing CRP3, the primary bootloader’s entry mechanism check will be bypassed. Fig 3 for CRP details.
Fig 2 Flash sectors in LPC11U68
Fig 3 Code Read Protection (CRP)
Secondary bootloader entry
The boot sequence shown below is used when entering the secondary USB bootloader.
Fig 4
Using an entry pin
The secondary USB bootloader will check the status of a GPIO pin to determine if it should enter into programming mode. This is the easiest way since no post processing is needed. And this secondary bootloader uses P0.16.
Automatic secondary bootloader entry
If the secondary USB bootloader detects that no user application is present upon reset, it will automatically enter programming mode.
ISP entry disabled
If the secondary USB bootloader detects that a user application has already been installed and that CRP is set to level 3, then it will not enter ISP mode.
Bootloader size
Since the bootloader resides within user programmable flash, it should be designed as small as possible. The larger the secondary USB bootloader is the less flash space is available to the user application. By default, the USB bootloader has been designed to fit within the first two flash sectors (Sector 0-1) so that the user application can start from sector 2.
Code placement in flash
The secondary bootloader is placed at the starting address 0x0 so that it will be executed by the LPC11U68 after reset. Flash programming is based on a sector-by-sector basis. This means that the code for
the user application should not be stored in any of the same flash sectors as the secondary bootloader and for efficient use of the flash space, the user application should be flashed into the next available empty sector after the bootloader.
In the application, the start sector is 3 (0x0000_3000) which is used to store the user application code.
User application execution
If the SW2 button is not depressed, the secondary bootloader will start the execution of the user application. Execution of the user application is performed by updating the stack pointer (SP) and program counter (PC) registers. The SP points to the new location where the user application has allocated the top of its stack .The PC on the other hand contains the location of the first executable instruction in the user application. From here on the CPU will continue normal execution and initializations specified on the user application. By default, the bootloader uses 2 flash sectors. Therefore, to utilize the remaining flash, the secondary bootloader will look for the user application at 0x00003000
Handing interrupts
The LPC11U68 contains a NVIC (Nested Vectored Interrupt Controller) that handles all interrupts. When an interrupt occurs the processor uses the vector table to locate the address of the handler.
On the LPC11U68 the vector table is located in the same area of flash memory as the secondary bootloader. The secondary bootloader is designed to be permanently resident in flash memory and therefore it is not possible to update the contents of the vector table every time a new application is downloaded.
The Cortex-M3 core allows the vector table to be remapped; however this is not the case with the Cortex-M0. Because of this, the secondary bootloader has been designed to redirect the processor to the handler listed in a vector table located in the application area of flash memory, see Fig 5.
Fig 5
User application
To execute the user application the secondary USB bootloader will load the new SP and PC values into their respective registers, allowing the CPU to execute the new code correctly. Therefore, the user application must be built so that it can run from that starting address. In the application, this address is 0x00003E00. So relocate the user application storage area by following corresponding IDE’s User Guide.
Testing
Creating the binary file
In this application, I build the demos_switch_blinky which is from the LPCOpen library to create the binary which is compatible with the secondary USB bootloader. The binary see Table 1.
08 04 00 10 B5 09 00 00 07 07 00 00 9B 09 00 00 00 00 00 00 00 00 00 00 00 00 00 00 A1 E1 FF EF 00 00 00 00 00 00 00 00 00 00 00 00 A7 09 00 00 00 00 00 00 00 00 00 00 E5 09 00 00 27 03 00 00 E3 09 00 00 E3 09 00 00 E3 09 00 00 E3 09 00 00 E3 09 00 00 E3 09 00 00 E3 09 00 00 E3 09 00 00 E3 09 00 00 E3 09 00 00 E3 09 00 00 E3 09 00 00 E3 09 00 00 E3 09 00 00 E3 09 00 00 E3 09 00 00 E3 09 00 00 E3 09 00 00 E3 09 00 00 E3 09 00 00 E3 09 00 00 E3 09 00 00 E3 09 00 00 E3 09 00 00 E3 09 00 00 01 03 00 00 E3 09 00 00 E3 09 00 00 E3 09 00 00 E3 09 00 00 E3 09 00 00 E1 09 00 00 FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF 38 B5 63 4C 25 68 28 07 07 D5 96 20 E0 60 61 48 00 78 00 28 01 D1 00 F0 F7 F8 20 68 0C 21 29 40 01 43 21 60 31 BD 38 B5 5A 4C A0 78 40 1C A0 70 C0 B2 65 28 34 DB 00 25 A5 70 20 78 00 28 2F D0 60 78 00 28 03 D0 02 28 16 D0 0A D3 20 E0 01 21 00 F0 CA F8 00 21 01 20 00 F0 C6 F8 00 21 02 20 13 E0 01 21 01 20 00 F0 BF F8 00 21 00 20 00 F0 BB F8 00 21 02 20 08 E0 01 21 00 F0 B5 F8 00 21 01 20 00 F0 B1 F8 00 21 01 20 00 F0 AD F8 00 E0 65 70 60 78 40 1C 60 70 C0 B2 03 28 00 DB 65 70 31 BD F8 B5 00 F0 36 F9 00 F0 C2 F8 3A 48 01 68 02 22 91 43 01 60 01 68 38 4A 0A 40 02 60 35 4F 01 20 38 70 36 48 00 68 0A 21 00 F0 2B F9 1E 21 00 F0 28 F9 40 1E 00 26 80 21 49 04 88 42 0C D2 30 49 48 60 30 48 02 68 12 02 12 0A C0 23 1B 06 13 43 03 60 8E 60 07 20 08 60 01 20 2B 49 08 60 23 4C 20 00 00 F0 18 F9 29 48 01 68 80 22 12 03 0A 43 02 60 20 68 01 21 01 43 21 60 20 68 01 21 88 43 20 60 20 68 80 21 88 43 20 60 A6 60 FA 20 80 00 60 60 20 68 40 21 01 43 21 60 20 68 80 21 01 43 21 60 20 68 80 20 80 04 1A 49 08 60 20 68 30 21 01 43 21 60 18 4D 28 78 00 28 12 D1 38 78 00 28 0E D0 00 21 00 20 00 F0 3E F8 00 21 01 20 00 F0 3A F8 00 21 02 20 00 F0 36 F8 FA 20 80 00 E0 60 3E 70 E8 7B 00 28 E6 D1 01 20 38 70 E3 E7 00 40 02 40 04 00 00 10 00 20 00 A0 FF FF FE FF 00 00 00 10 10 E0 00 E0 20 ED 00 E0 1C 80 04 40 14 82 04 40 00 E1 00 E0 01 00 00 A0 49 01 40 18 83 54 70 47 10 B5 32 4C 20 00 00 F0 BF F8 E1 21 49 02 20 00 00 F0 C7 F8 03 20 E0 60 81 20 A0 60 80 20 20 63 10 BD 00 00 03 28 00 DB 70 47 80 B5 01 23 4B 40 2D A1 0A 5C 2B A1 09 5C A0 20 00 06 FF F7 DC FF 01 BD 00 00 03 28 00 DB 70 47 10 B5 A0 21 09 06 24 A2 12 5C 92 00 89 18 8C 22 92 01 01 23 00 BF 21 A4 20 5C 83 40 8B 50 10 BD 00 00 F8 B5 FF F7 C7 FF A0 25 2D 06 28 00 00 F0 B6 F8 00 24 00 BF 18 A6 31 5D 88 00 28 18 80 22 92 01 80 18 00 BF 15 A2 12 5D 03 68 01 27 97 40 1F 43 07 60 01 23 28 00 FF F7 A9 FF 64 1C 03 2C EA DB F1 BD 00 00 80 B5 07 48 01 68 80 22 52 02 0A 43 02 60 19 22 0A A1 04 48 00 F0 98 F8 01 BD 00 00 00 80 00 40 80 80 04 40 00 40 04 40 80 B5 FF F7 E9 FF 00 F0 B1 F8 01 BD 02 02 02 00 11 10 12 00 00 03 81 00 00 04 81 00 00 05 81 00 00 08 81 00 00 09 81 00 00 0B 02 00 00 0C 02 00 00 0D 02 00 00 0E 02 00 00 12 81 00 00 13 81 00 00 17 01 00 01 09 01 00 01 0B 81 00 01 0E 81 00 01 14 82 00 01 15 82 00 01 16 81 00 01 17 82 00 01 1A 81 00 01 1B 81 00 01 1D 81 00 02 00 01 00 02 01 01 00 02 03 82 00 80 B5 00 F0 EF F8 01 49 08 60 01 BD 00 00 00 10 80 B5 03 4A 12 68 12 69 52 68 90 47 02 BD 00 00 F8 1F FF 1F 03 48 01 68 80 22 D2 05 0A 43 02 60 70 47 00 00 80 80 04 40 15 49 01 22 8A 61 0A 68 80 23 5B 01 13 43 0B 60 07 21 81 60 10 21 81 62 70 47 70 B5 04 00 0D 00 01 20 0E 49 08 60 00 F0 8F F8 06 00 29 01 FF F7 D3 FF 01 00 E0 68 80 22 02 43 E2 60 C8 B2 20 60 08 04 00 0E 60 60 E0 68 80 22 90 43 E0 60 30 00 FF F7 C2 FF 70 BD 00 00 80 80 04 40 98 80 04 40 02 48 01 68 40 22 0A 43 02 60 70 47 80 80 04 40 00 2A 00 D1 70 47 30 B4 0C 68 23 0C 25 0A E4 B2 00 2C 12 D0 02 2C 01 D0 0A D3 11 E0 ED B2 AC 00 04 19 02 2D 01 DB F4 25 00 E0 F0 25 63 51 07 E0 2D 06 AC 0D 04 19 23 66 02 E0 2D 06 AC 0D 03 51 09 1D 52 1E E0 D1 30 BC 70 47 FE E7 38 B5 20 20 00 F0 E8 F8 00 20 00 90 11 48 02 E0 00 99 49 1C 00 91 00 99 81 42 F9 DB 01 20 00 F0 1F F8 0D 48 01 68 01 24 03 22 91 43 21 43 01 60 80 20 00 F0 C7 F8 09 4D 23 20 28 60 80 20 00 F0 CB F8 68 68 C0 07 FC D5 2C 67 03 20 00 F0 10 F8 31 BD 00 00 C4 09 00 00 10 C0 03 40 08 80 04 40 42 49 FF E7 08 60 00 20 48 60 01 20 48 60 70 47 3F 49 F7 E7 43 A0 CA 05 12 0F 92 00 80 58 C9 06 C9 0E 49 1C 49 00 FF F7 49 FF 00 BD 00 B5 00 20 3B 49 03 22 8B 6E 13 40 11 D0 02 2B 11 D0 02 D3 03 2B 10 D0 00 BD 89 6B 0A 40 08 D0 01 2A 03 D0 03 2A 1A D1 31 48 00 E0 2F 48 00 68 00 BD 2D 48 00 BD C9 69 D6 E7 8B 6B 1A 40 08 D0 01 2A 03 D0 03 2A 05 D1 29 48 00 E0 27 48 00 68 00 E0 25 48 09 68 C9 06 C9 0E 49 1C 48 43 00 BD 00 00 00 00 10 B5 00 20 22 4C 03 21 A2 6E 0A 40 30 D0 02 2A 15 D0 21 D3 03 2A 2C D1 A2 6B 11 40 08 D0 01 29 03 D0 03 29 05 D1 19 48 00 E0 17 48 00 68 00 E0 14 48 21 68 C9 06 C9 0E 49 1C 48 43 19 E0 E1 69 14 A0 CA 05 12 0F 92 00 80 58 C9 06 C9 0E 49 1C 49 00 FF F7 EB FE 0C E0 A2 6B 11 40 08 D0 01 29 03 D0 03 29 05 D1 09 48 00 E0 07 48 00 68 00 E0 04 48 21 6F FF F7 DA FE 10 BD 00 00 40 80 04 40 70 80 04 40 00 1B B7 00 D0 09 00 00 D4 09 00 00 08 80 04 40 00 00 00 00 C0 27 09 00 90 05 10 00 C0 5C 15 00 F0 B3 1A 00 20 0B 20 00 00 9F 24 00 E0 32 29 00 C0 C6 2D 00 50 97 31 00 E0 67 35 00 70 38 39 00 00 09 3D 00 40 16 40 00 80 23 43 00 C0 30 46 00 0B 49 0A 68 10 43 09 4A 02 40 C8 20 00 02 10 43 08 60 70 47 06 49 0A 68 82 43 04 48 10 40 C8 22 12 02 02 43 0A 60 70 47 00 00 00 00 FF 25 00 00 38 82 04 40 70 B4 01 21 00 22 13 E0 04 68 00 1D 0C 42 02 D0 4D 46 6D 1E 64 19 22 60 24 1D 1B 1F 04 2B FA D2 25 00 9E 07 01 D5 22 80 AD 1C 0B 40 00 D0 2A 70 03 68 00 1D 00 2B E7 D1 70 BC 70 47 10 B5 07 49 79 44 18 31 06 4C 7C 44 16 34 04 E0 08 1D 0A 68 89 18 88 47 01 00 A1 42 F8 D1 10 BD 08 00 00 00 14 00 00 00 9D FF FF FF 08 00 00 00 00 00 00 10 00 00 00 00 00 F0 0B F8 00 28 01 D0 FF F7 DE FF 00 20 00 BF 00 BF FF F7 0C FD 00 F0 02 F8 01 20 70 47 80 B5 00 F0 02 F8 01 BD FE E7 07 46 38 46 00 F0 02 F8 FB E7 FE E7 20 21 09 03 26 31 18 20 AB BE F9 E7 01 48 80 47 01 48 00 47 D9 09 00 00 C5 09 00 00 00 BF 00 BF 00 BF 00 BF FF F7 D2 FF 00 1B B7 00 00 80 00 00 80 B5 FF F7 DF FD 01 BD FE E7 FE E7 FE E7 |
Table 1
Drag and drop the binary file
- Running the secondary bootloader, and connect a USB cable between the PC and the J3, see Fig 6;
Fig 6
- Drag and drop the binary file to the driver, see Fig 7;
Fig 7
- Review the values of the user application in the relative area , see Fig 8;
Fig 8
