Discovery Book: Rust

Discovering the world of microcontrollers through Rust! 🦀

This repository is to hold code used and in conjunction with working through material in the Discovery-Book for learning embedded rust.

Getting Started: Testing the Hardware

$ openocd -f interface/stlink-v2-1.cfg -f target/stm32f3x.cfg
Open On-Chip Debugger 0.10.0
Licensed under GNU GPL v2
For bug reports, read
        http://openocd.org/doc/doxygen/bugs.html
Info : auto-selecting first available session transport "hla_swd". To override use 'transport select <transport>'.
adapter speed: 1000 kHz
adapter_nsrst_delay: 100
Info : The selected transport took over low-level target control. The results might differ compared to plain JTAG/SWD
none separate
Info : Unable to match requested speed 1000 kHz, using 950 kHz
Info : Unable to match requested speed 1000 kHz, using 950 kHz
Info : clock speed 950 kHz
Info : STLINK v2 JTAG v37 API v2 SWIM v26 VID 0x0483 PID 0x374B
Info : using stlink api v2
Info : Target voltage: 2.896991
Info : stm32f3x.cpu: hardware has 6 breakpoints, 4 watchpoints

The microcontroller in the F3 has a Cortex-M4F processor in it. rustc knows how to cross compile to the Cortex-M architecture and provides 4 different targets that cover the different processor families within that architecture:

• thumbv6m-none-eabi, for the Cortex-M0 and Cortex-M1 processors
• thumbv7m-none-eabi, for the Cortex-M3 processor
• thumbv7em-none-eabi, for the Cortex-M4 and Cortex-M7 processors
• thumbv7em-none-eabihf, for the Cortex-M4F and Cortex-M7F processors

Binary size is something we should always keep an eye on! How big is your solution? You can check that using the size command on the release binary:

$ # equivalent to size target/thumbv7em-none-eabihf/debug/led-roulette
$ cargo size --target thumbv7em-none-eabihf --bin led-roulette -- -A
led-roulette  :
section               size        addr
.vector_table          392   0x8000000
.text                16404   0x8000188
.rodata               2924   0x80041a0
.data                    0  0x20000000
.bss                     4  0x20000000
.debug_str          602185         0x0
.debug_abbrev        24134         0x0
.debug_info         553143         0x0
.debug_ranges       112744         0x0
.debug_macinfo          86         0x0
.debug_pubnames      56467         0x0
.debug_pubtypes      94866         0x0
.ARM.attributes         58         0x0
.debug_frame        174812         0x0
.debug_line         354866         0x0
.debug_loc             534         0x0
.comment                75         0x0
Total              1993694

$ cargo size --target thumbv7em-none-eabihf --bin led-roulette --release -- -A
led-roulette  :
section              size        addr
.vector_table         392   0x8000000
.text                1826   0x8000188
.rodata                84   0x80008ac
.data                   0  0x20000000
.bss                    4  0x20000000
.debug_str          23334         0x0
.debug_loc           6964         0x0
.debug_abbrev        1337         0x0
.debug_info         40582         0x0
.debug_ranges        2936         0x0
.debug_macinfo          1         0x0
.debug_pubnames      5470         0x0
.debug_pubtypes     10016         0x0
.ARM.attributes        58         0x0
.debug_frame          164         0x0
.debug_line          9081         0x0
.comment               18         0x0
Total              102267

Know how to read this output? The text section contains the program instructions. It's around 2KB in my case. On the other hand, the data and bss sections contain variables statically allocated in RAM (static variables). A static variable is being used in aux5::init; that's why it shows 4 bytes of bss.

Chapter 6: Hello World!