Flushing all d-cache may be a long operation. We need to send keep_alive regularly to keep the connection alive. If not done a warning is emitted. Change-Id: I52c3ee9a9f9b8a1dc0b8d5439e8b71212f56165a Signed-off-by: Adrien Grassein <agrassein@nanoxplore.com> Signed-off-by: Adrien Charruel <acharruel@nanoxplore.com> Reviewed-on: https://review.openocd.org/c/openocd/+/8659 Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com> Tested-by: jenkins