To buffer or not to buffer

May 19, 2024

The DMA-based UART driver in JeeH is an interesting example of the interaction between hardware, memory use, and blocking behaviour. Reading data # In JeeH, the way to read bytes from the UART is to send a message to its device driver, and wait for its reply. The mTag field is 'R', with the mLen and mPtr field starting off as zero. The driver uses a small ring buffer internally, which is filled in via DMA as bytes arrive. ...

The next task is Tasks

April 21, 2024

As mentioned in my previous Threads vs Async I/O musings, threads are no longer the main concurrency mechanism I’m after, tasks are. Threads are still present in JeeH (and they actually work), but I’m not so keen on having to allocate stacks for each thread, nor on deciding up front how large they need to be. So what is a task? # Tasks are a bit different. I’m using the same sys::send and sys::recv mechanism for them as threads and device drivers, but they run as part of the thread which created them. ...

JeeH 5.4.0

April 2, 2024

JeeH version 5.4.0 release notes and highlights: This is mostly to consolidate what there is, to prepare for a new v6 series of releases (the reason is described in this post - in short: I want to redo the tasks-vs-threads design and the test automation). Changes in v5.4.0: More work on a RAM-based test runner, using openocd to upload the code. Explore more ways to send test output through ITM/SWO, which avoids the need to dedicate a UART to this. ...

Spring cleaning

March 28, 2024

Looks like it’s that time of year again: I’m ripping apart what I have in JeeH 5.3 and reconstructing it in a different way. Perhaps it’s just madness, but I have two reasons to do this: 1) the task/thread design is too messy and 2) the way I can add and run tests is too tedious. Tasks vs threads # The first issue was unavoidable, once I figured out that tasks should not be an add-on to a threaded system, but exactly the other way around: threads are a special kind of task. ...

JeeH 5.3.0

March 9, 2024

JeeH version 5.3.0 release notes and highlights: This release brings a number of major changes: Tasks have been renamed to Threads … because that’s what they really are. And with that out of the way: a new Task type has been added, to support asynchronous processing, i.e. an “async/await” style of doing work which does not run in a separate thread. This reduces overhead and avoids the need for a separate stack. ...

Threads vs Async I/O

March 3, 2024

It was a mistake in JeeH to call something a Task when it really is a Thread, so I’ve decided to rename them everywhere in the code and in the documentation. Threads are separate execution contexts, each with their own stack. And that’s what’s in JeeH right now. Threads # Threads are a bit of a double-edged sword: yes, you can nicely modularise different parts of an application this way, especially in the context of a µC where lots of external events and interrupts are going on. ...

JeeH 5.2.0

February 12, 2024

JeeH version 5.2.0 release notes and highlights: This is the most extensive release so far, with new SDIO and Ethernet drivers. Everything is still highly experimental, but the main pieces of the multitasker puzzle are starting to fit together quite nicely. Using lightweight messages as the main vehicle for communication between tasks and drivers works really well and allows pacing the different pieces of an application. The driver model helps decouple the different layers, as illustrated by the eth driver and net worker task: neither one needs knowledge of the other (their code can be included in either order). ...


December 22, 2023

Musings ≠ weblog. The site used to be my old weblog. For a fairly long time I posted there on a daily basis. Lots of topics I wanted to write about, as I discovered Arduino’s, the whole field of “physical computing”, and then went on to produce and sell JeeNodes, JeeLinks, JeePlugs, etc. It was great fun while it lasted, but at some point I ran out of fuel. ...