Blogs

Previously published This article was previously published on lhexapod.com as part of my journey of discovery into robotics and embedded assembly programming. A full index of these articles can be found here. The new functionality in my servo control takes more memory to implement due to the more complex state that we need to maintain for each servo. The simple controller could support up to 64 PWM channels on the ATTiny2313, the more advanced controller can, at the present stage of the design, support around 15.

I’m developing the simple client server protocol code that I’m harvesting in a test driven manner. Although the code exists, as such, and I’m harvesting it rather than inventing it from scratch the harvesting is taking the “best” ideas from several similar implementations to create the version that will form part of the framework’s example code. As such I’m treating this just like a new development and, mostly, writing my tests first.

The simple client/server request/response protocol that I’m currently harvesting uses the concept of an ‘invocation’ to tie a request to a response. An id is generated on the client and placed in the request header. The server simply copies the id from the request header to the response header and the client can then match responses to requests. This works nicely but the implementation has evolved with the protocol. The first version used a 4 byte invocation id, allocated an instance of an invocation data class and stored the allocation address of the object as the invocation id.

Previously published This article was previously published on lhexapod.com as part of my journey of discovery into robotics and embedded assembly programming. A full index of these articles can be found here. So far the servo controller development has been reasonably straight forward; once various design issues were considered and once I’d got my head around building the hardware and learning AVR assembly language. However I expect that my assembly code has many novice mistakes and that it’s probably not especially idiomatic.

Quite often my customers use The Server Framework for both ends of their communication channels. The Server Framework has fully supported developing clients as well as servers for a long time now and although many of my customers build either servers or clients with the framework some build both. One of the things that often comes up in discussions with these customers is how to develop a custom request/response protocol for their servers and clients to communicate with.

Previously published This article was previously published on lhexapod.com as part of my journey of discovery into robotics and embedded assembly programming. A full index of these articles can be found here. Part of the new functionality that I’m developing for the serial servo controller for my hexapod robot is for the servo controller to take its time in moving a servo from where it is at the moment to where I want it to be.

Previously published This article was previously published on lhexapod.com as part of my journey of discovery into robotics and embedded assembly programming. A full index of these articles can be found here. One of the problems of moving from the simple three byte SSC style control system to a system where we can do clever things with multiple servos at once is that the data required to do these clever things is bigger than the data required to do the simple things.

Previously published This article was previously published on lhexapod.com as part of my journey of discovery into robotics and embedded assembly programming. A full index of these articles can be found here. To be able to implement the new commands for the servo controller I need to adjust the data that we use to control the servos. Right now we have a single byte per servo and that byte contains a value between 0 and 254 which represents the length of the pulse sent to the servo.

Previously published This article was previously published on lhexapod.com as part of my journey of discovery into robotics and embedded assembly programming. A full index of these articles can be found here. I now have an easy to extend PWM servo controller and the next job on my list of things to do is extend it so that it supports the functionality that I feel I need for correct control of my hexapod’s legs.

Previously published This article was previously published on lhexapod.com as part of my journey of discovery into robotics and embedded assembly programming. A full index of these articles can be found here. The 64 channel serial servo controller that I’ve been developing works pretty well for me but most of my development and testing was done in the AVR studio simulator. Once I actually started working with my hardware again I noticed a slight problem.