HelenOS sources

TSD0              404 uspace/drv/nic/rtl8139/driver.c 	void *tsd = rtl8139->io_port + TSD0 + tx_curr * 4;
TSD0              685 uspace/drv/nic/rtl8139/driver.c 		void *tsd_to_check = rtl8139->io_port + TSD0 +
HelenOS homepage, sources at GitHub