blockdiag download_procedure_diagram {
    node_height = 40;
    node_width = 150;
    span_width = 40;
    span_height = 45;
    default_fontsize = 12
    orientation = portrait;
    edge_layout = flowchart;
    default_group_color = none;

    // nodes
    start [label = "Start", shape = flowchart.terminator];
    init [label = "Initialization", shape = box];
    success_cond [label = "Success?", shape = flowchart.condition];
    erase_data [label = "Erase data", shape = box];
    transmit_data [label = "Transmit data", shape = box];
    finish_cond [label = "Finish?", shape = flowchart.condition];
    transmit_finish [label = "Transmit finish frame", shape = box];
    finish [label = "Finish", shape = flowchart.terminator];
    // fake nodes to adjust shape and edge label position
    succ_fin [shape = none];
    fincon_fin [shape = none];

    // edges
    start -> init -> success_cond;
    success_cond -> erase_data [label = "Yes"];
    erase_data -> transmit_data;
    transmit_data -> finish_cond;
    success_cond -- succ_fin [label = "Failure"];
    finish_cond -> transmit_finish [label = "Yes"];
    finish_cond -- fincon_fin [label = "Failure"];
    succ_fin -- fincon_fin;
    fincon_fin -> finish;
    transmit_finish -> finish;

    // group
    group{transmit_finish, fincon_fin};
    group{erase_data, succ_fin};
}
