NAT_TIMESTAMP_LSB
val = reg_encode(reg, NAT_TIMESTAMP_LSB, NAT_TIMESTAMP_SHIFT);
[NAT_TIMESTAMP_LSB] = GENMASK(20, 16),
[NAT_TIMESTAMP_LSB] = GENMASK(20, 16),
[NAT_TIMESTAMP_LSB] = GENMASK(20, 16),
[NAT_TIMESTAMP_LSB] = GENMASK(20, 16),
[NAT_TIMESTAMP_LSB] = GENMASK(20, 16),
[NAT_TIMESTAMP_LSB] = GENMASK(20, 16),