HelenOS sources

DP_CNTR0          340 uspace/drv/nic/ne2k/dp8390.c 	pio_read_8(ne2k->port + DP_CNTR0);
DP_CNTR0          602 uspace/drv/nic/ne2k/dp8390.c 		for (errors = pio_read_8(ne2k->port + DP_CNTR0); errors > 0; --errors)
HelenOS homepage, sources at GitHub