Embedded Timer Explorer

This is hosted live on GitHub Pages if you're looking for that.

This is a toy design analysis utility meant to support decisions around configuring a timer on a microcontroller. The initial configuration is an example meant to partially represent the possible configuration space for timer 0 on a PIC18F66K40.

Features

• Architecture- and device-agnostic
• Selection of a target timer expiry duration
• Selection of the timer's counter bit width
• Representation of multiple, fixed clock source frequencies
• Representation of multiple scalers (potentially pre-scalers or post-scalers) showing how their factor product affects the configuration space
• Scaler series in predefined, linear-range, or binary-exponential-range mode
• Display of the feasible configuration space region as a projection of the actual bounding polytope
• Mouse-over information including timer value and accuracy
• Solution-culling by maximum absolute relative error

Math

In this system, the independent variables are:

• bit width
• clock frequency
• pre-scale and post-scale factor
• expiry time

The dependent variables are:

• timer value
• resolution
• error

The fundamental equation being modelled is

value * scale = time * freq

under the following constraint:

1 <= value < 2^bits

Relative error is calculated as:

time_actual / time_ideal - 1

Reload integers

The timer reload value is represented as a modified two's-complement integer; with a 16-bit integer as an example:

• Zero (0x0000) is identical
• The negative portion (0x8000 through 0xFFFF representing -32768 through -1) is identical
• The other half - 0x0001 through 0x7FFF - rather than representing positive numbers - represents the negative numbers from -65535 through -32769

This is to facilitate low-fuss, direct entry of an integer that will transparently convert to the correct machine code representation while still being easily understood as a timer value with no positive-negative discontinuity. This transparent conversion has worked in all of the compilers I've tried, most recently XC8; but of course you'll want to test this for yourself.