A decoding apparatus has an on-chip buffer, an external buffer interface, and a turbo decoder. The on-chip buffer is arranged for buffering each code block to be decoded. The external buffer interface is arranged for accessing an off-chip buffer. The turbo decoder is arranged for decoding a specific code block read from the on-chip buffer. The specific code block is not transmitted from the on-chip buffer to the off-chip buffer via the external buffer interface unless decoding fail of the specific code block is identified.