c++ CRTP design pattern and mixin

http://www.thinkbottomup.com.au/site/blog/C%20%20_Mixins_-_Reuse_through_inheritance_is_good

C++ concurrency

1. http://www.developerfusion.com/article/138018/memory-ordering-for-atomic-operations-in-c0x/

2. http://locklessinc.com/articles/futex_cheat_sheet/

Linux PCIE & DMA tutorials

1. http://en.wikipedia.org/wiki/PCI_configuration_space

2. https://www.kernel.org/doc/Documentation/DMA-API-HOWTO.txt

3. http://linuxgazette.net/156/jangir.html

4. http://www.tldp.org/LDP/tlk/dd/pci.html

5. https://lkml.org/

6. http://bbs.chinaunix.net/forum.php?mod=forumdisplay&fid=227&page=1

C++ Idioms

http://en.wikibooks.org/wiki/More_C%2B%2B_Idioms:

enable_if implementation:

=== Solution and Sample code===
The enable_if templates are very simple syntactically. They always come in pairs: one of them is empty and the other one has a <code>type</code> typedef that forwards its second type parameter. The empty structure triggers an invalid type because it contains no member. When a compile-time condition is false, the empty <code>enable_if</code> template is chosen. Appending <code>::type</code> would result in an invalid instantiation, which the compiler throws away due to the SFINAE principle.

<source lang="cpp">
template <bool, class T = void>
struct enable_if
{};

template <class T>
struct enable_if<true, T>
{
  typedef T type;
};

</source>

Here is an example that shows how an overloaded template function can be selected at compile-time based on arbitrary properties of the type parameter. Imagine that the function '''T foo(T t)''' is defined for all types such that T is arithmetic. The enable_if template can be used either as the return type, as in this example:

<source lang="cpp">
template <class T>
typename enable_if<is_arithmetic<T>::value, T>::type
foo(T t)
{
  // ...
  return t;
}
</source>

or as an extra argument, as in the following:

<source lang="cpp">
template <class T>
T foo(T t, typename enable_if<is_arithmetic<T>::value >::type* dummy = 0);
</source>

The extra argument added to foo() is given a default value. Since the caller of foo() will ignore this dummy argument, it can be given any type. In particular, we can allow it to be void *. With this in mind, we can simply omit the second template argument to '''enable_if''', which means that the '''enable_if<...>::type''' expression will evaluate to ''void'' when '''is_arithmetic<T>''' is true.

Whether to write the enabler as an argument or within the return type is largely a matter of taste, but for certain functions, only one alternative is possible:
* Operators have a fixed number of arguments, thus '''enable_if''' must be used in the return type.
* Constructors and destructors do not have a return type; an extra argument is the only option.
* There does not seem to be a way to specify an enabler for a conversion operator. Converting constructors, however, can have enablers as extra default arguments.

gdb cast

In gdb you have to put single-quotes around scoped C++ names, e.g.:

  p *('bd::Main' *)pb_pip_thread_data->bd_pb_

data_msg.main_ms

or:

p *('abc::def::ghi' *)0x123456

Instead of gdb, run gdbtui. Or run gdb with the -tui switch. Or press C-x C-a after entering gdb. Now you're in GDB's TUI mode.
Enter layout asm to make the upper window display assembly -- this will automatically follow your instruction pointer, although you can also change frames or scroll around while debugging. Press C-x s to enter SingleKey mode, where run continue up down finish etc. are abbreviated to a single key, allowing you to walk through your program very quickly.

   +---------------------------------------------------------------------------+
B+>|0x402670 <main>         push   %r15                                        |
   |0x402672 <main+2>       mov    %edi,%r15d                                  |
   |0x402675 <main+5>       push   %r14                                        |
   |0x402677 <main+7>       push   %r13                                        |
   |0x402679 <main+9>       mov    %rsi,%r13                                   |
   |0x40267c <main+12>      push   %r12                                        |
   |0x40267e <main+14>      push   %rbp                                        |
   |0x40267f <main+15>      push   %rbx                                        |
   |0x402680 <main+16>      sub    $0x438,%rsp                                 |
   |0x402687 <main+23>      mov    (%rsi),%rdi                                 |
   |0x40268a <main+26>      movq   $0x402a10,0x400(%rsp)                       |
   |0x402696 <main+38>      movq   $0x0,0x408(%rsp)                            |
   |0x4026a2 <main+50>      movq   $0x402510,0x410(%rsp)                       |
   +---------------------------------------------------------------------------+
child process 21518 In: main                            Line: ??   PC: 0x402670
(gdb) file /opt/j64-602/bin/jconsole
Reading symbols from /opt/j64-602/bin/jconsole...done.
(no debugging symbols found)...done.
(gdb) layout asm
(gdb) start
(gdb)

Learn VHDL

There is a VHDL book on-line: http://tams-www.informatik.uni-hamburg.de/vhdl/doc/cookbook/VHDL-Cookbook.pdf My advice, as with any language, is to start hacking it. What I would do is get AvNet's Spartan 3A dev kit: http://www.xilinx.com/products/devkits/aes_sp3a_eval400_avnet.htm Why? It's got all you need, and it's only $50. Next, I would read the tutorial for the kit (free with registration on AvNet). This will walk you though the structure of a basic VHDL program. Then, I would extend that to do something need, using the book and the web as a reference as necessary.

IPs of a multicast socket

There are 3 IPs a multicast socket might need, 

1. before joining a multicast group, we need to bind the socket, what does this bind do?
    1) it tells the kernel which port this application want the data from;

     2) it tells the kernel what dest address the incoming packet should have. 

 

     so if we say any (0.0.0.0), any incoming packet with the correct port number will be forwarded to the app;  if we say only x.y.z.d, 

     then only the packets with that addr will be forwarded to the app, others will be dropped;

 

    For a multicast group, ideally should be the multicast ip or 0.0.0.0, cannot think of a 3rd case, unless we want to join several multicast 

    groups, but want to filter out some traffic here, but I am doubting we will ever need this. 

2. When join a group, we need to provide the multicast addr, this is easy to understand;  We also want to tell the kernel from which interface

    this group's traffic will come from, if we don't specify it will be any, the kernel will select one for you(definitely, not all interfaces, so this might not works as you want), this is done

    by local ip. 

IP_ADD_MEMBERSHIP.

Recall that you need to tell the kernel which multicast groups you are interested in. If no process is interested in a group, packets destined to it that arrive to the host are discarded. In order to inform the kernel of your interests and, thus, become a member of that group, you should first fill aip_mreqstructure which is passed later to the kernel in theoptvalfield of thesetsockopt()system call.

The ip_mreq structure (taken from/usr/include/linux/in.h) has the following members:

struct ip_mreq
{
        struct in_addr imr_multiaddr;   /* IP multicast address of group */
        struct in_addr imr_interface;   /* local IP address of interface */
};

(Note: the "physical" definition of the structure is in the file above specified. Nonetheless, you should not include<linux/in.h>if you want your code to be portable. Instead, include<netinet/in.h>


which, in turn, includes<linux/in.h>itself).

The first member,imr_multiaddr, holds the group address you want to join. Remember that memberships are also associated with interfaces, not just groups. This is the reason you have to provide a value for the second member:imr_interface. This way, if you are in a multihomed host, you can join the same group in several interfaces. You can always fill this last member with the wildcard address (INADDR_ANY) and then the kernel will deal with the task of choosing the interface.

With this structure filled (say you defined it as:struct ip_mreq mreq;) you just have to callsetsockopt()this way:

setsockopt (socket, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq));

Notice that you can join several groups to the same socket, not just one. The limit to this isIP_MAX_MEMBERSHIPSand, as of version 2.0.33, it has the value of 20

6.1 IP_MULTICAST_LOOP.

You have to decide, as the application writer, whether you want the data you send to be looped back to your host or not. If you plan to have more than one process or user "listening", loopback must be enabled. On the other hand, if you are sending the images your video camera is producing, you probably don't want loopback, even if you want to see yourself on the screen. In that latter case, your application will probably receive the images from a device attached to the computer and send them to the socket. As the application already "has" that data, it is improbable it wants to receive it again on the socket. Loopback is by default enabled.

Regard thatoptvalis a pointer. You can't write:

setsockopt(socket, IPPROTO_IP, IP_MULTICAST_LOOP, 0, 1);

to disable loopback. Instead write:

u_char loop;
setsockopt(socket, IPPROTO_IP, IP_MULTICAST_LOOP, &loop, sizeof(loop));

and setloopto 1 to enable loopback or 0 to disable it.

To know whether a socket is currently looping-back or not use something like:

u_char loop;
int size;

getsockopt(socket, IPPROTO_IP, IP_MULTICAST_LOOP, &loop, &size)

6.2 IP_MULTICAST_TTL.

If not otherwise specified, multicast datagrams are sent with a default value of 1, to prevent them to be forwarded beyond the local network. To change the TTL to the value you desire (from 0 to 255), put that value into a variable (here I name it "ttl") and write somewhere in your program:

u_char ttl;
setsockopt(socket, IPPROTO_IP, IP_MULTICAST_TTL, &ttl, sizeof(ttl));

The behavior withgetsockopt()is similar to the one seen on IP_MULTICAST_LOOP.

6.3 IP_MULTICAST_IF.

Usually, the system administrator specifies the default interface multicast datagrams should be sent from. The programmer can override this and choose a concrete outgoing interface for a given socket with this option.

struct in_addr interface_addr;
setsockopt (socket, IPPROTO_IP, IP_MULTICAST_IF, &interface_addr, sizeof(interface_addr));

>From now on, all multicast traffic generated in this socket will be output from the interface chosen. To revert to the original behavior and let the kernel choose the outgoing interface based on the system administrator's configuration, it is enough to callsetsockopt()with this same option andINADDR_ANYin the interface field.

In determining or selecting outgoing interfaces, the following ioctl

s might be useful:SIOCGIFADDR(to get an interface's address),SIOCGIFCONF(to get the list of all the interfaces) andSIOCGIFFLAGS(to get an interface's flags and, thus, determine whether the interface is multicast capable or not -theIFF_MULTICASTflag-).

If the host has more than one interface and the IP_MULTICAST_IF option is not set, multicast transmissions are sent from the default interface, although the remainding interfaces might be used for multicast forwarding if the host is acting as a multicast router.