Bluetooth to serial modules have been around almost forever. Just connect power, ground, RXD, TXD, maybe a config pin and you have a trivial way to transmit data wirelessly from an embedded system to a PC or Android device.
Continue reading “Beware of JDY-30 Bluetooth SPP modules”
I2C remains a popular communication interface between MCUs and all kinds of auxiliary chips like ADCs, digipots and GPIO expanders. I had to make a simple and universal driver for an upcoming STM32L432 project to control Microchip digipots. STM32 I2C peripheral is simple enough to use without the burden of HAL libraries, additionally I needed a custom driver because my application uses FreeRTOS.
Continue reading “STM32L4 I2C driver for FreeRTOS without HAL”
This is a driver for STM32L432 LPUART. It should also work with the “full” UART. The LPUART is a simple peripheral (compared to the clock tree or ADC). In this case it is easier to master the usage of a couple of registers, than use full-size HAL drivers, as they are very generic to cover every possible flavor of a peripheral across the whole STM32 line, which in turn makes them big in terms of code size and actually harder to follow than the register layout.
The driver can be safely used within FreeRTOS, It can even be used by multiple tasks, but it probably would make little sense anyway, unless there can be different devices connected at runtime to the same UART or the application has separate operating modes implemented in different tasks.
Continue reading “STM32L4 UART driver for FreeRTOS without HAL”
Generating arbitrary signals using an MCU is extremely useful. It can be used for example to play back any audio or make a modulator for a modem. The most needed MCU peripheral is of course a DAC, but it also needs other peripherals to efficiently play back the samples without loading the CPU.
This post shows how to implement a signal generator on an STM32L432 without using HAL libraries.
Runtime memory corruption is one of the worst class of bugs a C/C++ application can have. I do not mean design problems like abuse of global variables, but seemingly correct code clobbering memory it should never touch (for example due to runaway pointers). Compared to “regular” crashes that are obvious and much simpler to fix (even if they are rare they leave a stacktrace), memory corruption is often silent. It can go unnoticed for a long period and manifest itself in subtle ways. For example: the application sometimes acts weirdly or a particular variable is sometimes wrong. Fortunately Cortex-M3 and M4 cores are equipped with special hardware that can assist in catching rogue memory accesses.
Continue reading “Cortex-M – Debugging runtime memory corruption”
Debugging embedded systems during development even with the best tools can be hard. Certainly a good debug probe makes life easier, but what do you do after the product is shipped? What if the customer complains that something strange is happening sometimes or a bug makes the device reboot, but only once a week? You make the firmware gather diagnostic information for you. This is the first post in series.
Continue reading “Preserving debugging breadcrumbs across reboots in Cortex-M”
The C standard library (libc) is a component that gets little attention. It is just there. However for embedded systems it brings some challenges and overhead in terms of code size. As firmware size is often critical, it sometimes makes sense to use a trimmed version of the standard library or to remove it entirely. I will focus on reducing the code size that may be beneficial for a small application like a bootloader.
Continue reading “Reducing firmware size by removing libc”
Link-time optimization is a powerful output size reducing feature. Even though (as of 2018) still regarded as somewhat experimental, LTO is worth trying, if the binary size is very important and the application can be reliably tested afterwards, as link-time optimized code is hard to debug. A bootloader can be an ideal example. LTO is very easy to enable, but there are some small quirks that have to be taken care of. I will use GCC 7.2.1 from GNU Arm Embedded as an example.
Continue reading “Fixing Cortex-M startup code for link-time optimization”
Running out of disk space is a common problem for unattended Linux boxes like database servers or backup storage servers. Usually I would use Zabbix (or Nagios) do to the monitoring, but it would be an overkill for a Raspberry Pi or a single NAS, so I made a small Bash script. This script runs df, checks disk usage and sends mail in case the free space is running low.
Continue reading “Disk space monitoring & e-mail notifications with Bash”
Fourier transform is a vast domain of knowledge with many practical applications within signal processing. Virtually all communications protocols use Fourier transform at one step or another (including LTE, GPS and WiFi). Another popular example are the “jumping bars” in music players showing levels of low and high tones in real time. In this post I show the basics of obtaining spectrum of an audio signal on an EFM32 Cortex-M3 microcontroller. No scary math!
Continue reading “Practical FFT on microcontrollers using CMSIS DSP”