One of the problems I want to address in JeeH, is how to best interface with peripherals: built-in as well as connected via a common bus, e.g. I2C or SPI. There are two sides to this: talking to built-in hardware via device registers, and talking through built-in hardware to a connected module / chip. Hardware register access # Talking to the built-in hardware is a matter of reading and writing the hardware registers at specific addresses. ...
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. ...
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. ...
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. ...
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. ...
Musings ≠ weblog. The jeelabs.org 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. ...