Date: Wed, 09 May 2001 16:13:53 +0200 From: Oscar-Ivan Lepe-Aldama <oscar@ac.upc.es> To: net@freebsd.org Subject: On the workings of the xl dirver Message-ID: <3AF950A1.2D4A13F2@ac.upc.es>
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Hi,
I would like to have information regarding the implementation of the
xl_start_90xB function in the xl driver. After reading the code and the
technical reference from 3com I still cannot understand how the driver
signals the NIC for packet downloading. I know the code is OK as my
FreeBSD box, loaded with a pair of 3C905B-TX NICs, works just fine: it
forwards packets. But because I am interested in measuring the
performance of the system (both software and hardware) I need to know
the points where the software signals the hardware. Please help. Some
details follow.
In the case of the xl_start function (the xl driver has two
implementations of the if_start operation: xl_start_90xB for 3c90xB NICs
and xl_start for others) this is clear. It uses the following code,
which follows the algorithm presented in the technical reference:
2276 /*
2277 * Queue the packets. If the TX channel is clear, update
2278 * the downlist pointer register.
2279 */
2280 CSR_WRITE_2(sc, XL_COMMAND, XL_CMD_DOWN_STALL);
2281 xl_wait(sc);
2282
2283 if (sc->xl_cdata.xl_tx_head != NULL) {
2284 sc->xl_cdata.xl_tx_tail->xl_next = start_tx;
2285 sc->xl_cdata.xl_tx_tail->xl_ptr->xl_next =
2286 vtophys(start_tx->xl_ptr);
2287 sc->xl_cdata.xl_tx_tail->xl_ptr->xl_status &=
2288 ~XL_TXSTAT_DL_INTR;
2289 sc->xl_cdata.xl_tx_tail = cur_tx;
2290 } else {
2291 sc->xl_cdata.xl_tx_head = start_tx;
2292 sc->xl_cdata.xl_tx_tail = cur_tx;
2293 }
2294 if (!CSR_READ_4(sc, XL_DOWNLIST_PTR))
2295 CSR_WRITE_4(sc, XL_DOWNLIST_PTR,
vtophys(start_tx->xl_ptr));
2296
2297 CSR_WRITE_2(sc, XL_COMMAND, XL_CMD_DOWN_UNSTALL);
But in the case of the xl_start_90xB the code is like this:
2426 /* Start transmission */
2427 sc->xl_cdata.xl_tx_prod = idx;
2428 start_tx->xl_prev->xl_ptr->xl_next = start_tx->xl_phys;
As can be seen in this last case, there are no CSR_WRITE operations for
signaling the NIC. However, the technical reference says the NIC has to
be signaled for it to learn there is work to do. How is this being
implemented is this case? Thanks.
Best regards,
--
========================================================================
0 0 0 Oscar-Ivan Lepe-Aldama | UPC-Campus Nord, DAC
0 0 0 e-mail: oscar@ac.upc.es | Modul D6, despatx 116
0 0 0 phone: +34 93 401 7187 | Jordi Girona, 1-3
U P C fax: +34 93 401 7055 | 08034 Barcelona - SPAIN
WWW: http://www.ac.upc.es/homes/oscar/
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