diff --git a/RESOURCES.md b/RESOURCES.md
new file mode 100644
index 0000000..8eba88f
--- /dev/null
+++ b/RESOURCES.md
@@ -0,0 +1,43 @@
+# Rust Raspberry Pi Pico / Rust rp2040 Resources
+
+Setup your Rust installation for rp2040 development:
+
+```
+# Add the rp2040 CPU architecture:
+rustup self update
+rustup update stable
+rustup target add thumbv6m-none-eabi
+
+# Useful to creating UF2 images for the RP2040 USB Bootloader
+cargo install elf2uf2-rs --locked
+
+# Useful for flashing over the SWD pins using a supported JTAG probe
+cargo install --git https://github.com/rp-rs/probe-run.git --branch rp2040-support 
+
+# flip-link detect stack-overflows on the first core
+# (which is the only supported target for now.)
+cargo install flip-link
+```
+
+A broad overview of the rp2040 Rust ecosystem:
+
+- [Github rp-rs org](https://github.com/rp-rs/)
+  - [rp2040-project-template](https://github.com/rp-rs/rp2040-project-template)
+    You will find infos to setup Rust, probe-run and flip-link here.
+  - [rp-hal - rp2040 Hardware Abstraction Layer](https://github.com/rp-rs/rp-hal)
+    You will find other useful setup information here.
+    - [pico Rust examples](https://github.com/rp-rs/rp-hal/tree/main/boards/pico/examples)
+    - [rp2040-hal examples](https://github.com/rp-rs/rp-hal/tree/main/rp2040-hal/examples)
+- elf2uf2 converter: `cargo install elf2uf2-rs --locked`
+- [Raspberry Pi Pico DapperMime CMSIS-DAP Debug Probe UF2 Image](https://github.com/majbthrd/DapperMime/releases/download/20210225/raspberry_pi_pico-DapperMime.uf2)
+  - See also: https://github.com/rp-rs/rp2040-project-template/blob/main/debug_probes.md
+- [heapless - statically allocated data structures](https://docs.rs/heapless/0.7.8/heapless/)
+- [Cortex-M allocator](https://crates.io/crates/alloc-cortex-m)
+Use with care, and "it's probably safer to reserve heap space with linker scripts!"
+
+## Assorted Projects / Crates
+
+- [ithinuel ws2812-pio-rs - ws2812 driver that uses the PIO peripheral](https://github.com/ithinuel/ws2812-pio-rs/)
+  - There is an example for this here: https://github.com/rp-rs/rp-hal/blob/main/boards/feather_rp2040/examples/feather_neopixel_rainbow.rs
+- [WeirdConstructor's collection of Rust stuff](https://github.com/WeirdConstructor/RustRP2040Code)
+  - Code for a PWM driven DAC that sythesizes sine and saw waveforms: https://github.com/WeirdConstructor/RustRP2040Code/blob/master/pwm_dac_saw_sampling/src/main.rs
diff --git a/pwm_dac_saw_sampling/src/main.rs b/pwm_dac_saw_sampling/src/main.rs
index 2a83e27..fe46e5c 100644
--- a/pwm_dac_saw_sampling/src/main.rs
+++ b/pwm_dac_saw_sampling/src/main.rs
@@ -67,6 +67,15 @@ fn main() -> ! {
 
     use num_traits::float::FloatCore;
 
+    // Formular for RC filter cutoff calc (WLambda):
+    // !fc = {!(r, c) = @; 1.0 / (2.0 * 3.14159265359 * r * c) };
+    // >> fc 40.0 0.000000100
+    // > 39788.735772971224
+
+    use alloc;
+    let x : Vec<f32> = alloc::vec::Vec::new();
+    x.push(0.2);
+
     let sin =
         unsafe {
             core::mem::transmute::<_, fn(f32) -> f32>