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Re: [Discuss-gnuradio] Switching flow between two paths.

From: Jeon
Subject: Re: [Discuss-gnuradio] Switching flow between two paths.
Date: Fri, 27 Mar 2015 14:23:11 +0900

After thinking about it for a couple of days, I've decided not to use two separated RLL blocks.
Instead, I made a block as below:

In work() function:

get_tags_in_range(tags, 0, nitems_read(0),
        nitems_read(0) + ninput_items[0],
RLL_CODE rll_code = (RLL_CODE)pmt::to_long(tags[0].value);

// ... omitted trivial things

switch (rll_code) {
        for(int i = 0; i < ninput_items[0]; i++) {
            out[2 * i]     = !!in[i];
            out[2 * i + 1] =  !in[i];
    case RLL4B6B:
        for(int i = 0; i < ninput_items[0] / 4; i += 4) {
            int rll4B = 0;
            for (int j = 0; j < 4; j++) {
                // make four bits into one bytes
                rll4B |= (in[i + j] & 1) << j;
            for (int j = 0; j < 6; j++) {
                // put six bits corresponding to rll4B
                out[6 * i + j] = !!(rll4B6B[rll4B] & (1 << j));

// mapping definition

const char rll4B6B[16] = {
    0b011100,    0b101100,    0b110010,    0b011010,
    0b101010,    0b110001,    0b011001,    0b101001,
    0b100110,    0b010110,    0b001110,    0b100011,
    0b010011,    0b100101,    0b010101,    0b001101

If the code are not formatted well and hard to read, please refer: https://gist.github.com/gsongsong/f3e34991a55f29dac5d2
There might be some syntax violation and variable definitions missing, I apologize for that.
And please note that each in[i] is either 0b00000000 or 0b00000001.

By using a tag, RLL coding scheme are not changing during the stream.
Currently, I haven't built it and tested yet.

What do you think of it?

I will make some notes after build and test the entire system.


2015-03-26 23:17 GMT+09:00 Kevin Reid <address@hidden>:
On Mar 25, 2015, at 2:15, Marcus Müller <address@hidden> wrote:

> source -+--> custom_block0 ---> encoder0 ---> add -->
>         +--> custom_block1 ---> encoder1 ------^
> you'd need to implement custom_block in python or C++, that would either
> pass through items, just like the block does that comes out of
> gr_modtool add -l python -t sync
> or set the output items to 0. You'd toggle that behavior exactly at the
> sample that you get a tag.

Note that if you don't actually need the switch to happen at a specific point in the stream, but you still want the switch to be atomic (guaranteed not to drop or repeat any items), the existing multiply_matrix block can do the switching in this flowgraph: it would be configured with one input and two outputs, and setting the matrix to either [[0, 1]] or [[1, 0]].

(Of course, the disadvantage of either of these strategies is that you're paying the CPU cost of both encoders all of the time.)

Kevin Reid                                  <http://switchb.org/kpreid/>

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