Monday, September 1, 2008

The channel woes

Today I was trying to register an asterisk channel. However my module registration failed with the error that module does not provide any description. I had half a mind to edit the line from Loader.c and load my module. However, I also noticed that I was compiling the module for one version (SVN trunk) and using it on some other version (1.4.15).

Then I downloaded asterisk from svn and compiled and installed it on some other machine. Then I just put in my simple module code, compiled, copied to /usr/lib/asterisk/modules/ and on the command line told "module load chan_thin" The stuff that was not happening for last two days just happened!

The sad part of my story is this. Till now the asterisk was giving me this message: "Module '' does not provide a description". I had tried various things including injecting the code of AST_MODULE_INFO macro into my module and adding checks on the functions used by that macro. I kept getting that vague error only because of some version change. (OK, it is still my mistake. Lot of things could have happened in a version change)

Anyway, now I have a module that goes in and does nothing. I have also checked oss channel driver in asterisk. I feel that is the most simple channel driver which I can use as a datum. More on it later. Before I end, let me put down a partial function call tree.

1. AST_MODULE_INFO -> Defines the module info and the register function. This registers ast_module_info
2. load_module -> This is made available to asterisk using ast_module_info structure. It is called when we load the module. For channel registration, ast_channel_register is called during load module. It passes a structure ast_channel_tech
3. ast_channel_tech -> This has all the callback functions. For OSS channel, the structure is as follows.

static struct ast_channel_tech oss_tech = {
.type = "Console",
.description = tdesc,
.capabilities = AST_FORMAT_SLINEAR, /* overwritten later */
.requester = oss_request,
.send_digit_begin = oss_digit_begin,
.send_digit_end = oss_digit_end,
.send_text = oss_text,
.hangup = oss_hangup,
.answer = oss_answer,
.read = oss_read,
.call = oss_call,
.write = oss_write,
.write_video = console_write_video,
.indicate = oss_indicate,
.fixup = oss_fixup,

4. oss_request -> This is the function that is called by asterisk when a call comes to your channel. The number is passed to you as a parameter to the function.

Got to do few more things. Rest later.

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