The analog/digital converter unit is one of the most complicated units implemented in the project. The unit can measure the voltage on an input pin, either as its immediate value, or averaged with exponential forgetting. Isochronous sampling is available as well: It's possible to capture a fixed-length block of data on demand, or as a response to a triggering condition on any of the enabled input pins. The ADC must continuously sample the inputs to make the averaging and level based triggering possible; As a consequence, a pre-trigger buffer is available that can be read together with the block of samples following a trigger. The ADC unit can also be switched to a continuous streaming mode.
It's possible to activate any number of the 16 analog inputs of the ADC peripheral simultaneously. The maximum continuous sampling frequency, which reaches 70\,ksps with one channel, lowers with an increasing number of enabled channels as the amount of data to transfer to the host increases.
# - defines the maximum pre-trigger size (divide by # of channels)
# - captured data is sent in half-buffer chunks
# - buffer overrun aborts the data capture
buffer_size=256
# Enable continuous sampling with averaging
# Caution: This can cause DAC output glitches
averaging=Y
# Exponential averaging coefficient (permil, range 0-1000 ~ 0.000-1.000)
# - used formula: y[t]=(1-k)*y[t-1]+k*u[t]
# - not available when a capture is running
avg_factor=500
\end{inicode}
\subsection{ADC Events}
\begin{cmdlist}
50 &\cname{TRIGGERED}
The first event generated when a triggering condition occurs. The payload includes pre-trigger and the transaction continues with a sequence of CAPTURE events sharing the same frame ID. The serial number is incremented with each stream chunk and can be used to detect lost data frames.
