Some news from the ben-wpan driver front: Stefan Schmidt did some great work on the atusb driver, based on Richard Sharpe's skeleton driver. I then killed a few remaining bugs.
All the kernel code is in the ben-wpan branch of http://projects.qi-hardware.com/index.php/p/qi-kernel/ Now I got some clean pings between a Ben equipped with atben and a PC equipped with atusb, both running dirtpan: 100 packets transmitted, 100 received, 0% packet loss, time 99524ms rtt min/avg/max/mdev = 152.010/158.962/176.015/5.154 ms The round-trip-time is quite long. This it at least in part because it seems that I can get only one USB control transfer per 1 ms frame, which means that the very best-case timing for a send-receive turnaround (on one end) is 23 ms. Sometimes, a control transfer also takes longer. A ping over dirtpan exchanges a total of four frames: the Echo Request, an ACK generated by dirtpan, the Echo Reply, and finally an ACK for the Echo Reply. I don't see anything in the USB specification that would require control transfers to be so slow, but I haven't been able to find any mechanism in the kernel to make them faster either. Ideas welcome :-) dirtpan has relatively short timeouts. To make it work in this scenario, the timeouts have to be enlarged, see the patch below. One additional complication is that atben turns around faster than atusb, so the ACK for a frame sent from atusb to atben is usually lost, and it takes the two a while to resolve the problem. As a dirty work-around, I just make dirtpan's send_ack wait until we can be reasonably sure the peer has turned around. The long turn-around time also effectively breaks any serious use of TCP (SSH or such), probably because of TCP ACK loss. If there's no easy solution for getting control transfers handled more quickly, then it will be necessary to move more of the send/receive logic from the kernel driver into the firmware. - Werner ---------------------------------- cut here ----------------------------------- diff --git a/tools/dirtpan/dirtpan.c b/tools/dirtpan/dirtpan.c index 5e6d200..22a20fa 100644 --- a/tools/dirtpan/dirtpan.c +++ b/tools/dirtpan/dirtpan.c @@ -61,8 +61,8 @@ enum packet_type { #define MAX_FRAG (127-11-2-1) /* MHDR, FCS, control byte */ #define MAX_PACKET 2000 #define MAX_TRIES 5 -#define T_REASS_MS 200 -#define T_ACK_MS 50 +#define T_REASS_MS 500 +#define T_ACK_MS 100 static struct { @@ -323,6 +323,7 @@ static void send_ack(int seq) { uint8_t ack = pt_ack | (seq ? SEQ : 0); +usleep(4000); send_frame(&ack, 1); stats.tx_ack++; } _______________________________________________ Qi Hardware Discussion List Mail to list (members only): [email protected] Subscribe or Unsubscribe: http://lists.en.qi-hardware.com/mailman/listinfo/discussion
