Re: Fwd: [Myricom help #8335] [Q] two questions...

Hi,

> I spent lots of time to find where my bug lives and finally arrived here.
> A pointer operation used in my MCP shows very strange result. To simplfy
> my question, I list some parts of my code below.
> 
> int gap;
> mem_info_t mem_table[MAX];
> mem_info_t *mem_ptr;
> 
> mem_ptr = &mem_table[index];
> gap = mem_ptr-&mem_table[0];                    // (a)
> gap = gap / 16;                                 // (b)
> 
> After line (a) is executed, the variable 'gap' shows 17. But after
> line (b) is executed the variable 'gap' shows 4 (not 1).    ;-)
> By shifting 'gap' 4 bits instead of dividing by 16, (gap = gap >> 4), I can
> continue to work(fortunately the divisor is in the power of 2.).
> I'm using lanai-gcc version 2.95.2..1.4. In fact I don't think the lanai-gcc
> has a bug, but I can not understatnd this result. If my word is discourteous
> I apologize to Myricom team.

There is no division support in the Lanai instruction set. Everything 
should be bits shifting. I should admit that I have never tried to 
compile a such division. Glenn would know more about that.

> 2. loopback packet is not received.
> I expect that a packet sent from node A to itself is received to
> verify that a switch is still alive. I filled up all the bytes in the
> routing header with 0x80 and set SA to 7. (I'm using 8 bytes routing
> header in my MCP.) But no packet is received. I have no problem for
> communication among different nodes. A packet sent from node A is received
> by node B. (node A should not be the same node as node B.) But a loopback
> packet is not received. How can I solve this problem?

Why do you use 8 bytes for the route if you send a loopback packet, 
ie crossing only one crossbar ?!? Each crossbar "eats" one routing 
byte in the routing header. If you put 8 routing bytes, you are expecting 
to cross 8 crossbars (a very long loopback :-) ).

Refer to the specs (Annexe B of VITA) at
http://www.myri.com/open-specs/index.html

Patrick

----------------------------------------------------------
|   Patrick Geoffray, Ph.D.      [email protected] 
|   Myricom, Inc.                http://www.myri.com
|   Cell:  865-389-8852          685 Emory Valley Rd (B)
|   Phone: 865-425-0978          Oak Ridge, TN 37830
----------------------------------------------------------