Fix frequency rounding

- Use less DMAs
- Improve bit counting
- Fix sample_rate changes and other fixes

.gitignore

@@ -1,3 +1,2 @@
 /build/
 /grc/*.py
-/src/.clangd

README.md

@@ -2,9 +2,11 @@
 
 Using RP2040 / Raspberry Pi Pico as a software-defined radio receiver.
 
-See the [blog post](https://blog.porucha.net/2024/pico-sdr/) for more information. Older code the article is mostly referring to can be found in the branch `old` and a more up-to-date approach in the branch `master`.
+See the [blog post](https://blog.porucha.net/2024/pico-sdr/) for more information. Older code the article is mostly referring to can be found in the branch `old`.
 
-This branch contains code to use RP2040 with a 1:4 multiplexer and some passives as a quadrature sampling decoder receiver. It is still very much work in progress.
+## Circuit
+
+![](circuit.svg)
 
 ## Software
 
@@ -30,4 +32,4 @@ This branch contains code to use RP2040 with a 1:4 multiplexer and some passives
 
 4. Open `grc/PicoSDR-WBFM.grc` in GNU Radio Companion, adjust carrier frequency to match your favorite FM radio station and press `F6`.
 
-5. Alternatively [gqrx](https://www.gqrx.dk/) works fine with `rtl_tcp` input mode. Maximum sample rate seem to be 400 ksps, above that the samples are dropped. Make sure to experiment with LNA gain. It might be digital, but it's supposed to be somewhere north of 12 dB.
+5. Alternatively [gqrx](https://www.gqrx.dk/) works fine with `rtl_tcp` input mode. Maximum sample rate seem to be 400 ksps, above that the samples are dropped. Make sure to adjust LNA gain to +30 dB. It's not accurate, but it does control bias strength which in turn does affect analog gain.

grc/PicoSDR-WBFM.grc

@@ -49,7 +49,7 @@ blocks:
   id: variable
   parameters:
     comment: ''
-    value: '200_000'
+    value: '192_000'
   states:
     bus_sink: false
     bus_source: false
@@ -374,7 +374,7 @@ blocks:
     freq7: 100e6
     freq8: 100e6
     freq9: 100e6
-    gain0: '6'
+    gain0: '0'
     gain1: '10'
     gain10: '10'
     gain11: '10'

grc/PicoSDR.grc

@@ -401,7 +401,7 @@ blocks:
     freq7: 100e6
     freq8: 100e6
     freq9: 100e6
-    gain0: '30'
+    gain0: '0'
     gain1: '10'
     gain10: '10'
     gain11: '10'

tools/clangd.py

@@ -1,50 +0,0 @@
-#!/usr/bin/env python
-
-import os.path
-import sys
-from glob import glob
-
-import click
-import yaml
-
-
-@click.command()
-def clangd():
-    """Generate .clangd file for local development."""
-
-    assert "PICO_SDK_PATH" in os.environ, "PICO_SDK_PATH not set"
-
-    pico_sdk_path = os.path.realpath(os.environ["PICO_SDK_PATH"])
-    cwd = os.path.realpath(os.getcwd())
-
-    includes = [
-        *glob(f"{pico_sdk_path}/src/common/*/include"),
-        *glob(f"{pico_sdk_path}/src/rp2040/*/include"),
-        *glob(f"{pico_sdk_path}/src/rp2_common/*/include"),
-        f"{pico_sdk_path}/lib/tinyusb/src",
-        *glob(f"{cwd}/src/**/include", recursive=True),
-        f"{cwd}/build/generated/pico_base",
-        f"{cwd}/build/sdk",
-    ]
-
-    flags = [
-        "-Wall",
-        "-Wextra",
-        "-xc",
-        "-DCFG_TUSB_MCU=OPT_MCU_RP2040",
-        "-I/usr/arm-none-eabi/include",
-    ]
-
-    yaml.safe_dump(
-        {
-            "CompileFlags": {
-                "Compiler": "arm-none-eabi-gcc",
-                "Add": [*flags, *[f"-I{inc}" for inc in includes]],
-            }
-        },
-        sys.stdout,
-    )
-
-
-if __name__ == "__main__":
-    clangd()

util/bridge.py

@@ -62,10 +62,6 @@ def bridge(frequency, device):
 
             print("Begin")
 
-            header = fp.read(12)
-            if header:
-                peer.send(header)
-
             try:
                 cmd = b""