Receivers commonly estimate the frequency offset on a block that is downstream relative to the frequency correction NCO. In such architectures, typically the frequency offset estimator feeds the estimation back to the NCO. Until now, this was not possible if using the rotator block as the NCO. This patch adds a message port to the rotator block such that the referred feedback architecture becomes feasible. A downstream block can estimate the frequency offset and send a message to the rotator block to update its rotating frequency (i.e., its phase increment). The requesting block can schedule the phase increment update to a specific absolute sample index. This feature is useful for receivers that rely on a frame structure and pilot-aided frequency offset estimation. If the true frequency offset is allowed to change at any random instant throughout the frame, the frame-averaged frequency offset estimation can become less reliable. Instead, it is often better to update the frequency correction right at the start of a new frame. With that, the true frequency offset is preserved in the course of a frame and only changes around the boundary between consecutive frames. For flexibility when using this feature, it is the responsibility of the downstream block to schedule the phase increment update properly. For example, if there is a decimator in between the rotator block and the frequency offset estimator, the latter will need to take the sample rate conversion into account when defining the absolute sample offset when the update should be applied. Besides, the rotator block can now place a tag on the sample where it updates the phase increment. This allows a downstream block to better calibrate and validate the scheduling of phase increment updates. Signed-off-by: Igor Freire <igor@blockstream.com>