Picocalc_SD_Boot is a custom bootloader for the Raspberry Pi Pico. This bootloader provides the functionality to load and execute applications from an SD card, designed to enable PicoCalc to load firmware to the Pico using an SD card easily.
work in progress plans Feature Request Post
- Avoiding the need to recompile Apps, A/B image see Address Translation (see page 364 of the RP2350 datasheet, section 5.1.19)
- Support for .uf2 files, extract
.binfrom.uf2firmware pico-bootrom - USB Mass Storage mode for SD card. Related Demo Code
Click the button above to download the prebuilt .uf2 firmware for the Picocalc_SD_Boot bootloader. Flash your pico with holding BOOT_SEL and drag and drop the .uf2 file.
Clone the source code and initialize the submodules.
git clone https://github.com/adwuard/Picocalc_SD_Boot.git
cd Picocalc_SD_Boot
git submodule update --init --recursiveBuild the bootloader.
cd ./src
mkdir build; cd build
cmake ..
make🚨 Important Note: 🚨
Applications intended for SD card boot "MUST REBUILD" using a custom linker script to accommodate the program's offset address.
✅ You can find all the recompiled firmware available in the sd_card_content folder.
This section explains how to build and deploy applications on an SD card. Below is a simple example of a CMakeLists.txt for an application.
Copy memmap_sdcard_app.ld to your project repository.
cmake_minimum_required(VERSION 3.13...3.27)
include(vendor/pico_sdk_import.cmake)
add_subdirectory(pico-sdcard-boot)
project(hello)
set(FAMILY rp2040)
set(CMAKE_C_STANDARD 11)
set(CMAKE_CXX_STANDARD 17)
pico_sdk_init()
add_executable(hello main.c)
target_link_libraries(hello PRIVATE pico_stdlib)
pico_enable_stdio_usb(hello 1)
pico_add_extra_outputs(hello)
# ----------- COPY THIS Section -----------
function(enable_sdcard_app target)
#pico_set_linker_script(${target} ${CMAKE_SOURCE_DIR}/memmap_sdcard_app.ld)
if(${PICO_PLATFORM} STREQUAL "rp2040")
pico_set_linker_script(${CMAKE_PROJECT_NAME} ${CMAKE_SOURCE_DIR}/memmap_default_rp2040.ld)
elseif(${PICO_PLATFORM} MATCHES "rp2350")
pico_set_linker_script(${CMAKE_PROJECT_NAME} ${CMAKE_SOURCE_DIR}/memmap_default_rp2350.ld)
endif()
endfunction()
# ----------- COPY THIS Section END -----------The enable_sdcard_app() function sets the necessary memmap_sdcard_app.ld linker script for projects that boot from an SD card.
- Build the project using the above CMakeLists.txt.
mkdir build; cd build
PICO_SDK_PATH=/path/to/pico-sdk cmake ..
makeOnce the build is complete, copy the generated APP_FW.bin file to the /sd directory of the SD card.
The bootloader implements a safe update mechanism with the following features:
- The bootloader itself resides in a protected flash area (first 256KB) that is never overwritten during updates
- Only the application region of flash (starting at 256KB) is updated using
flash_range_eraseandflash_range_program - The bootloader verifies if the update differs from the current flash image before performing any write operations
- Flash programming operations are executed from RAM using the
__not_in_flash_funcattribute to ensure safe execution while the flash is being modified - Program size is verified to prevent overwriting critical memory regions
When updating flash memory, the code that performs the flash operations must not be executed from the flash itself. The bootloader ensures this by:
- Using the Raspberry Pi Pico SDK's
__not_in_flash_funcattribute for all flash programming functions - This attribute ensures the functions are executed from RAM rather than flash
- Without this protection, attempting to modify the flash while executing code from it could lead to unpredictable behavior or bricking the device
- Hiroyuki Oyama: Special thanks for the firmware loader mechanism and VFS file system.
- TheKiwil: Special thanks for contributions on supporting pico2 boards with new custom linker script.
- Blog on this repository, and more technical detail about bootloader. -->Blog Page
- Fourm Page and Discussion: Clockwork Pi Fourm