Plain Servo Example

I will use the next days to wrap up a working version of the VM so I can test code footprint and performance. What I expect is actually quite high overall performance. Each instruction will be significantly slower than an ARM instruction -probably in the region of 1:1000, so I am hoping for an instruction speed of 50,000++. This will however be a learning experience.

Raw performance alone is however not that important, having a responsive system that we can use to control advanced operations with a few lines of code is. With a correct written Plain application a module will spend it’s life in idle waiting for an event from C code and respond to that.

Use System
Module Servo32
            Enum Byte ChannelMode
                        DigitalIn
                        DigitalOut
                        AnalogueIn
                        AnalogueOut
                        PWMOut
                        Servo
            End

            Object Channel
                        ChannelMode mode       
                        uint32 frequency
                        uint32 duty
                        uint32 servoPosition
                        real32 analogueValue
                        bit digitalValue
            End

            External C Channel chan[32]

            External C Func UpdateChannel(uint32 c)
            Event FrequencyError
            Event DutyError
            Event PositionError
            Event AnalogueError
            End

            External C Func EnableEvent(uint32 c)

            External C Event ChannelChanged(uint32 c)
                        if(chan[c].digitalValue=1)
                                   chan[c-4].servoPosition = 180
                        else
                                   chan[c-4].servoPosition = 0
                        end
                        UpdateChannel(c-4)
            End

            int16 x

            for x=1 to 4
                        chan[x].mode = ChannelMode.Servo
                        chan[x].frequency=50
                        chan[x].servoPosition=0
                        UpdateChannel (x)
            end

            for x=5 to 8
                        chan[x].mode = ChannelMode.DigitalIn
                        UpdateChannel (x)
            end

            for x=5 to 8
                        EnableEvent(x)
            end
End

The code snip above is an attempt to create a test program for the 32 x Servo/IO Hat. In this case I connect 4 servoes to channel 1-4 and a digital switch to channel 5-8. If I set channel 5 high I want servo 1 to move to pos 180 etc.

The actual Plain program is in this case 20 instructions and probably < 200 bytes of stored instruction Space.

Pay attention to event “ChannelChanged“. The rest of the code is just configuration, this event is the actual control code. What should happen is that as the digital input on channel 5-8 change we receive a call from C code and change the relevant servo channel as a response. After that we go back to idle and just wait for an event.

Binding to C code is planned to be done automatically by “External C”. In the example of ChannelEvent the RTL will expect to find a C event with that exact name and parameter. It’s too early to say if this will stand ground as I implement the VM – lets see.

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