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-rw-r--r--src/modules/controllib/blocks.cpp8
1 files changed, 7 insertions, 1 deletions
diff --git a/src/modules/controllib/blocks.cpp b/src/modules/controllib/blocks.cpp
index 04cb023a8..0175acda9 100644
--- a/src/modules/controllib/blocks.cpp
+++ b/src/modules/controllib/blocks.cpp
@@ -293,10 +293,16 @@ int blockIntegralTrapTest()
float BlockDerivative::update(float input)
{
- float output = 0.0f;
+ float output;
if (_initialized) {
output = _lowPass.update((input - getU()) / getDt());
} else {
+ // if this is the first call to update
+ // we have no valid derivative
+ // and so we use the assumption the
+ // input value is not changing much,
+ // which is the best we can do here.
+ output = 0.0f;
_initialized = true;
}
setU(input);