HelenOS sources

DP_IMR            309 uspace/drv/nic/ne2k/dp8390.c 	pio_write_8(ne2k->port + DP_IMR,
DP_IMR            621 uspace/drv/nic/ne2k/dp8390.c 	pio_write_8(ne2k->port + DP_IMR,
DP_IMR            149 uspace/drv/nic/ne2k/ne2k.c 		ne2k_cmds[3].addr = ne2k->base_port + DP_IMR;
HelenOS homepage, sources at GitHub