BPP_HCR_DSS_MASK
hw->hw_hcr = ((ack_rate<<BPP_HCR_DSS_SHFT)&BPP_HCR_DSS_MASK)
_bpp_set(hw_hcr, BPP_HCR_DSS_MASK|BPP_HCR_DSW_MASK);