Error post pada codeigniter

index.php

<div class="md-modal md-effect-13 addcontact" id="modal-13">
	<div class="md-content">
		<h3 class="f-26">Pemasukan</h3>
		<div>
			<form action="<?=base_url('r/masuk');?>" method="POST">
			<div class="input-group">
				<span class="input-group-addon"><i class="icofont icofont-list"></i></span>
				<input type="text" class="form-control pname" name="nomor" value="<?=$no;?>" readonly="">
			</div>
			<div class="input-group">
				<span class="input-group-addon"><i class="icofont icofont-list"></i></span>
				<input type="text" class="form-control pname" name="keterangan" placeholder="Keterangan">
			</div>
			<div class="input-group">
				<span class="input-group-addon"><i class="icofont icofont-calendar"></i></span>
				<input type="text" class="form-control pname" name="tanggal" value="<?=date('Y/m/d');?>" readonly="">
			</div>
			<div class="input-group">
				<span class="input-group-addon"><i class="icofont icofont-bill-alt"></i></span>
				<input type="number" class="form-control pname" name="jumlah" placeholder="Jumlah">
			</div>
			<div class="text-center">
				<button type="submit" class="btn btn-primary waves-effect m-r-20 f-w-600 d-inline-block save_btn">Save</button>
				<button type="button" class="btn btn-primary waves-effect m-r-20 f-w-600 md-close d-inline-block close_btn">Close</button>
			</div>
		</form>
		</div>
	</div>
</div>

Controllernya R.php

	function masuk()
	{
		if ($this->session->userdata('username')) {
			$data = array(
				'nomor'			=> $this->input->post('nomor'),
				'keterangan'	        => $this->input->post('keterangan'),
				'tanggal' 		=> $this->input->post('tanggal'),
				'jumlah' 		=> $this->input->post('jumlah'),
				'jenis' 		=> 'masuk'
			);
			$input = $this->Pembukuan_model->pemasukan($data);
			if ($input){
				$this->session->set_flashdata('message', 'Data pemasukkan berhasil ditambahkan');
				redirect(base_url('r/index'));
			}else{
				$this->session->set_flashdata('message', 'Data pemasukan gagal ditambahkan');
				redirect(base_url('r/index'));
			}
		}else{
			redirect(base_url());
		}
	}

Errornya

itu knp ya gan? mohon bantuannya