Processing Audio With The RP2040

April 17, 2022 by Bryan Cockfield 9 Comments

The Raspberry Pi, although first intended as an inexpensive single-board computer for use in education, is now ubiquitous in electronics communities. Its low price as well as Linux platform and accessible GPIO make it useful in many places outside the classroom. But, if you want to abandon the ease-of-use in favor of an even lower price, the Raspberry Pi foundation makes that possible as well with the RP2040 chip, commonly found on the Pico. [Jason] shows us one way to make use of this powerful chip by putting one in an audio digital signal processing board.

While development boards are available for this chip, [Jason] has opted instead for a custom PCB which he designed himself and includes an integrated headphone amplifier and 3.5 mm audio jacks. To do the actual DSP work, the RP2040 chip uses three 12-bit ADC channels and 16 controllable PWM channels. The platform is also equipped with the TLV320AIC3254 codec from Texas Instruments. With all of this put together, he has a functioning open-source platform he calls the DS-Pi.

[Jason] has built this as a platform for guitar effects and as a customizable guitar amp modeler, but with a platform that is Arduino-compatible and fairly easy to program it could be put to use for anything involving other types of music or audio processing, like this specialized MIDI-compatible guitar effects platform which is built around the same processor.

Arming With An OS

April 13, 2022 by Al Williams 28 Comments

We see tons of projects with the infamous “Blue Pill” STM32 boards. They are cheap and plentiful and have a lot of great features, or at least they were before the chip shortage. I recently picked up a “Black Pill”, which is very similar but has an even more powerful processor. For a few bucks, you get an ARM CPU that can run at 100 MHz (but with USB, probably 96 MHz). There’s 512 kB of flash and 128 kB of RAM. There’s a USB type C port, and even a button and an LED onboard. The thing fits on a breadboard and you can program it with a cheap STLink dongle which costs about $10.

Of course, you then have to consider the software. The STM32Cube stuff is a lot to set up and learn but it does let you do just about anything you can imagine. Then there is the STM32Duino plug-in that lets you use it as a beefy Arduino. That works and is easy enough to set up. However, there’s also Mbed. The only problem is that Mbed doesn’t work right out of the box. Turns out, though, it isn’t that hard to set up. I’ll show you how easy it is to get things going and, next time, I’ll show you a practical example of a USB peripheral that uses the mBed RTOS features.

First Steps

Obviously, you are going to need a Black Pill. There are at least two choices but for as cheap as they are there is little reason not to get the STM32F411 version that has more memory. The DIP form factor will fit in whatever breadboard you happen to have and a USB C cable will power the board so unless you are driving a lot of external circuitry, you probably don’t need an external supply.

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Talking To A Texas Instruments Calculator

March 17, 2022 by Bryan Cockfield 20 Comments

Texas Instruments is a world-class semiconductors company, but unfortunately what they are best known for among the general public is dated consumer-grade calculators thanks to entrenched standardized testing. These testing standards are so entrenched, in fact, that TI has not had to update the hardware in these calculators since the early 90s. They still run their code on a Z80 microcontroller, but [Ben Heck] found himself in possession of one which has a modern ARM coprocessor in it and thus can run Python.

While he’s not sure exactly what implementation of Python the calculator is running, he did tear it apart to try and figure out as much as he could about what this machine is doing. The immediately noticeable difference is the ARM coprocessor that is not present in other graphing calculators. After some investigation of test points, [Ben] found that the Z80 and ARM chips are communicating with each other over twin serial lines using a very “janky” interface. Jankiness aside, eventually [Ben] was able to wire up a port to the side of the calculator which lets him use his computer to send Python commands to the device when it is in its Python programming mode.

While there are probably limited use cases for 1980s calculators to run Python programs, we can at least commend TI for attempting to modernize within its self-built standardized testing prison. Perhaps this is the starting point for someone else to figure out something more useful to put these machines to work with beyond the classroom too. We’ve already seen some TI-84s that have been modified to connect to the Internet, for example.

Thanks to [Nikša] for the tip!

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An Interview With Reinhard Keil

March 6, 2022 by Chris Lott 3 Comments

Over on the Embedded FM podcast, [Chris] and [Elecia] just released their interview with [Reinhard Keil] of compiler fame. [Reinhard] recounts the story of Keil’s growth and how it eventually became absorbed into Arm back in 2005. Along with his brother Günter, the two founded the company as Keil Software in the Americas, and Keil Elektronik in Europe. They initially made hardware products, but as the company grew, they became dissatisfied with the quality and even existence of professional firmware development tools of the day. Their focus gradually shifted to making a CP/M- and a PC-based development environment, and in 1988, they introduced the first C-compiler designed for the 8051 from the ground up.

Love it or hate it, the Arm Keil suite of µVision IDE and the MDK/Cx51 compiler have been around a long time and used by embedded developers in many industries. Although a free and restricted-use version is available, the license fees prevent most folks from getting very enthusiastic about it. Pricing aside, the µVision IDE has its critics: [Jay Carlson], who used every IDE under the sun a few years ago in his review of sub-one-dollar microcontrollers, opined that it was nothing more than a free editor you get with C51 or MDK-ARM. On the other hand, even [Jay] concedes is that every chip he tested was officially supported by Keil and worked out of the box. Another thing that is important to some users is being able to produce consistent binaries from old projects. This isn’t important for your one-off MQTT hot tub thermometer. But if you need to recompile firmware for a fifteen-year-old railroad signaling system that has multiple certifications and regulatory approvals, using the original compiler and library versions is a huge help.

[Reinhard] goes on to discuss various tools and systems being developed at Arm by his team, such as improvements and additions to the CMSIS suite, the transition of the online Mbed compiler to the new Keil Studio Cloud, and an Arm hardware virtualization tool for cloud-based CI verification. Lest you think everything at Arm is proprietary and expensive, he points out that Arm is a major contributor to the GCC project and the CMSIS components are open source. Even if you aren’t interested in Arm/Keil tools, do check out the interview — it’s quite interesting and touches on several topics of general interest to all firmware developers. Or if you prefer, read the interview when the transcript is completed.

Apple Falling Division

December 9, 2021 by Al Williams 23 Comments

[Paul Curtis] over at Segger has an interesting series of blog posts about calculating division. This used to be a hotter topic, but nowadays many computers or computer languages have support for multiplication and division built-in. But some processors lack the instructions and a library to do it might be less than ideal. Knowing how to roll your own might allow you to optimize for speed or space. The current installment covers using Newton’s algorithm to do division.

Steve Martin had a famous bit about how to be a millionaire and never pay taxes. He started out by saying, “First… get a million dollar. Then…” This method is a bit like that since you first have to know how to multiply before you can divide. The basic premise is twofold: Newton’s method let you refine an estimate of a reciprocal by successive multiplications and then multiplying a number a reciprocal is the same as dividing. In other words, if we need to divide 34 by 6, you could rewrite 34/6 to 34 * 1/6 and the answer is the same.

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Linux: Coming Soon To M1 Macbooks

November 17, 2021 by Bryan Cockfield 62 Comments

Regardless of the chipset or original intended use of any computer system, someone somewhere is going to want to try and run Linux on it. And why not? Linux is versatile and free to use as well as open-source, so it’s quite capable of running on almost anything. Of course, it takes a little while for the Linux folk to port the software to brand new hardware, but it’s virtually guaranteed that it’s only a matter of time before Linux is running on even the most locked-down of hardware, like the M1 MacBooks.

[Hector Martin] aka [marcan] has been hard at work getting Linux up and running on the latest Apple offerings with their ARM-based M1 processors. Since these are completely divorced from their x86 product line the process had to be worked from the ground up which included both booting Linux and modifying the kernel to include support for the hardware. [marcan] has a lot of hardware working such as the USB ports and the SD card slot, and notes that his setup is even compatible with the webcam notch included in the latest batch of MacBooks.

There are a few things still missing. He’s running Arch and doesn’t have the GPU configured yet, so all of the graphics are rendered in software. But he has put the computer through the wringer including running some computationally-intense software for nearly a full day before realizing that the machine wasn’t charging, which did not make much difference in performance. These machines are indeed quite capable with their new ARM chipsets and hopefully his work going forward will bring Linux to the rest of us who still use Macs even if they don’t want to run macOS.

ARM’s Chinese Venture Goes Sour

September 1, 2021 by Jenny List 69 Comments

We’re used by now to many of the more capable microcontrollers and systems-on-chip that we use having an ARM core at their heart. From its relatively humble beginings in a 1980s British home computer, the RISC processor architecture from Cambridge has transformed itself into the go-to power-sipping yet powerful core for manufacturers far and wide. This has been the result of astute business decisions over decades, with ARM’s transformation into a fabless vendor of cores as IP at its heart. Recent news suggests that perhaps the astuteness has been in short supply of late though, as it’s reported that ARM’s Chinese subsidiary has gone rogue and detatched from the mothership taking the IP with it.

It seems that the CEO of the Chinese company managed to retain legal power when sacked by the parent company over questionable ties with another of his ventures, and has thus been able to declare it independent of its now-former parent. It still has the ARM IP up to the moment of detatchment and claims to be developing its own new products, but it seems likely that it won’t receive any new ARM IP.

What will be the effect of this at our level? Perhaps we have already seen it, as more Chinese chips such as the cheaper STM32 clones are likely to get low-end ARM cores as a result. It seems likely that newer ARM IP will remain for now in more expensive non-Chinese chip families, but in the middle of a semiconductor shortage it’s likely that we wouldn’t notice anyway. Where it will have a lasting effect is in future Chinese joint ventures by non-Chinese chip companies. Seeing ARM’s then-owner Softbank getting their fingers burned in such a way is likely to provide a disincentive to other companies considering a similar course. Whether ARM will manage to resolve the impasse remains to be seen, but it can hardly be a help to the rocky progress of their Nvidia merger.