i16 -> s16 at even more places, README improvements, env_csdr_fixed_big_bufsize fix.

README.md

@@ -109,7 +109,7 @@ Data types are noted as it follows:
 - `f` is `float` (single percision)
 - `c` is `complexf` (two single precision floating point values in a struct) 
 - `u8` is `unsigned char` of 1 byte/8 bits (e. g. the output of `rtl_sdr` is of `u8`)
-- `i16` is `signed short` of 2 bytes/16 bits (e. g. sound card input is usually `i16`)
+- `s16` is `signed short` of 2 bytes/16 bits (e. g. sound card input is usually `s16`)
 
 Functions usually end as:
 
@@ -124,12 +124,14 @@ The following commands are available:
 - `csdr convert_f_u8` 
 - `csdr convert_s8_f`
 - `csdr convert_f_s8`
-- `csdr convert_i16_f` 
-- `csdr convert_f_i16`
+- `csdr convert_s16_f` 
+- `csdr convert_f_s16`
 
 How to interpret: `csdr convert_<src>_<dst>`
 You can use these commands on complex streams, too, as they are only interleaved values (I,Q,I,Q,I,Q... coming after each other).
 
+> Note: The the functions with `i16` in their names have been renamed, but still work (e.g. `csdr convert_f_i16`).
+
 #### csdr commands
 
 `csdr` should be considered as a reference implementation on using `libcsdr`. For additional details on how to use the library, check `csdr.c` and `libcsdr.c`.
@@ -157,6 +159,10 @@ It multiplies all samples by `gain`.
 
 It copies the input to the output.
 
+	through
+
+It copies the input to the output, while also displaying the speed of the data going through it.
+
 	none
 
 The `csdr` process just exits with 0.
@@ -349,6 +355,38 @@ The actual number of padding samples can be determined by running `cat csdr.c |
 
 It exchanges the first and second part of the FFT vector, to prepare it for the waterfall/spectrum display. It should operate on the data output from `logpower_cf`.
 
+	dsb_fc [q_value]
+
+It converts a real signal to a double sideband complex signal centered around DC. 
+It does so by generating a complex signal:
+* the real part of which is the input real signal,
+* the imaginary part of which is `q_value` (0 by default).
+With `q_value = 0` it is an AM-DSB/SC modulator. If you want to get an AM-DSB signal, you will have to add a carrier to it.
+
+	add_dcoffset_cc
+
+It adds a DC offset to the complex signal: `i_output = 0.5 + i_input / 2, q_output = q_input / 2`
+
+	convert_f_samplerf <wait_for_this_sample>
+
+It converts a real signal to the `-mRF` input format of [https://github.com/F5OEO/rpitx](rpitx), so it allows you to generate frequency modulation. The input signal will be the modulating signal. The `<wait_for_this_sample>` parameter is the value for `rpitx` indicating the time to wait between samples. For a sampling rate of 48 ksps, this is 20833.
+
+	fmmod_fc
+
+It generates a complex FM modulated output from a real input signal.
+
+	fixed_amplitude_cc <new_amplitude>
+
+It changes the amplitude of every complex input sample to a fixed value. It does not change the phase information of the samples.
+
+	mono2stereo_s16
+
+It doubles every input sample.
+
+	setbuf <buffer_size>
+
+See the [buffer sizes](#buffer_sizes) section.
+
 #### Control via pipes
 
 Some parameters can be changed while the `csdr` process is running. To achieve this, some `csdr` functions have special parameters. You have to supply a fifo previously created by the `mkfifo` command. Processing will only start after the first control command has been received by `csdr` over the FIFO.
@@ -371,6 +409,56 @@ By writing to the given FIFO file with the syntax below, you can control the shi
 	
 E.g. you can send `-0.05 0.02\n`
 
+#### Buffer sizes
+
+`csdr` has three modes of determining the buffer sizes, which can be chosen by the appropriate environment variables:
+* default: 16k or 1k buffer is chosen based on function,
+* dynamic buffer size determination: input buffer size is recommended by the previous process, output buffer size is determined by the process,
+* fixed buffer sizes.
+
+`csdr` uses two buffer sizes by **default**. 
+* For operations handling the full-bandwidth I/Q data from the receiver, a buffer size of 16384 samples is used.
+* For operations handling only a selected channel, a buffer size of 1024 samples is used (see `env_csdr_fixed_bufsize` in the code).
+
+`csdr` now has an experimental feature called **dynamic buffer size determination**, which is switched on by issuing `export CSDR_DYNAMIC_BUFSIZE_ON=1` in the shell before running `csdr`. If it is enabled:
+* All `csdr` processes in a DSP chain acquire their recommended input buffer size from the previous `csdr` process. This information is in the first 8 bytes of the input stream. 
+* Each process can decide whether to use this or choose another input buffer size (if that's more practical).
+* Every process sends out its output buffer size to the next process. Then it startss processing data.
+* The DSP chain should start with a `csdr setbuf <buffer_size>` process, which only copies data from the input to the output, but also sends out the given buffer size information to the next process.
+* The 8 information included in the beginning of the stream is:
+  * a preamble of the bytes 'C','S','D','R' (4 bytes),
+  * the buffer size stored as `int` (4 bytes).
+* This size always counts as samples, as we expect that the user takes care of connecting the functions with right data types to each other.
+
+> I added this feature while researching how to decrease the latency of a DSP chain consisting of several multirate algorithms.
+> For example, a `csdr fir_decimate_cc 10` would use an input buffer of 10240, and an output buffer of 1024. The next process in the chain, `csdr bandpass_fir_fft_cc` would automatically adjust to it, using a buffer of 1024 for both input and output.
+> In contrast to original expectations, using dynamic buffer sizes didn't decrease the latency much.
+
+If dynamic buffer size determination is disabled, you can still set a **fixed buffer size** with `export CSDR_FIXED_BUFSIZE=<buffer_size>`.
+
+For debug purposes, buffer sizes of all processes can be printed using `export CSDR_PRINT_BUFSIZES=1`.
+
+If you add your own functions to `csdr`, you have to initialize the buffers before doing the processing. Buffer size will be stored in the global variable `the_bufsize`.
+
+Example of initialization if the process generates N output samples for N input samples:
+
+    if(!sendbufsize(initialize_buffers())) return -2;
+
+Example of initalization if the process generates N/D output samples for N input samples:
+
+    if(!initialize_buffers()) return -2;
+    sendbufsize(the_bufsize/D);
+
+Example of initialization if the process allocates memory for itself, and it doesn't want to use the global buffers:
+
+    getbufsize(); //dummy		
+    sendbufsize(my_own_bufsize);
+
+Example of initialization if the process always works with a fixed output size, regardless of the input:
+
+    if(!initialize_buffers()) return -2;
+    sendbufsize(fft_size);
+
 #### Testbench
 
 `csdr` was tested with GNU Radio Companion flowgraphs. These flowgraphs are available under the directory `grc_tests`, and they require the <a href="https://github.com/simonyiszk/gr-ha5kfu">gr-ha5kfu</a> set of blocks for GNU Radio.  

csdr.c

@@ -95,9 +95,17 @@ char usage[]=
 "    logpower_cf [add_db]\n"
 "    fft_benchmark <fft_size> <fft_cycles> [--benchmark]\n"
 "    bandpass_fir_fft_cc <low_cut> <high_cut> <transition_bw> [window]\n"
-"    encode_ima_adpcm_i16_u8\n"
-"    decode_ima_adpcm_u8_i16\n"
+"    encode_ima_adpcm_s16_u8\n"
+"    decode_ima_adpcm_u8_s16\n"
 "    compress_fft_adpcm_f_u8 <fft_size>\n"
+"    flowcontrol <data_rate> <reads_per_second>\n"
+"    through\n"
+"    dsb_fc [q_value]\n"
+"    convert_f_samperf <wait_for_this_sample> \n"
+"    fmmod_fc\n"
+"    fixed_amplitude_cc <new_amplitude>\n"
+"    monos2stereo_s16\n"
+"    setbuf <buffer_size>\n"
 "    fft_exchange_sides_ff <fft_size>\n"
 "    \n"
 ;
@@ -288,7 +296,7 @@ int parse_env()
 		envtmp=getenv("CSDR_FIXED_BUFSIZE");		
 		if(envtmp) 
 		{
-			env_csdr_fixed_bufsize = atoi(envtmp);
+			env_csdr_fixed_big_bufsize = env_csdr_fixed_bufsize = atoi(envtmp);
 		}
 	}
 	envtmp=getenv("CSDR_PRINT_BUFSIZES");
@@ -1372,7 +1380,7 @@ int main(int argc, char *argv[])
 #ifdef USE_IMA_ADPCM
 #define IMA_ADPCM_BUFSIZE BUFSIZE
 
-	if(!strcmp(argv[1],"encode_ima_adpcm_i16_u8"))
+	if( (!strcmp(argv[1],"encode_ima_adpcm_i16_u8"))||(!strcmp(argv[1],"encode_ima_adpcm_s16_u8")) )
 	{
 		if(!sendbufsize(initialize_buffers()/2)) return -2;
 		ima_adpcm_state_t d;
@@ -1387,7 +1395,7 @@ int main(int argc, char *argv[])
 		}
 	}
 
-	if(!strcmp(argv[1],"decode_ima_adpcm_u8_i16"))
+	if( (!strcmp(argv[1],"decode_ima_adpcm_u8_i16"))||(!strcmp(argv[1],"decode_ima_adpcm_u8_s16")) )
 	{
 		ima_adpcm_state_t d;
 		d.index=d.previousValue=0;
@@ -1655,7 +1663,7 @@ int main(int argc, char *argv[])
 		}		
 	}
 
-	if(!strcmp(argv[1],"mono2stereo_i16"))
+	if((!strcmp(argv[1],"mono2stereo_i16"))||(!strcmp(argv[1],"mono2stereo_s16")))
 	{
 		if(!sendbufsize(initialize_buffers())) return -2;
 		float last_phase = 0;