# `defmt`
- [`defmt book`](https://defmt.ferrous-systems.com/introduction)

## `esp-println`
### Features
- The `defmt-espflash` adds framming bytes so `espflash` knows that is a `defmt` message
- Only usable when using `espflash`
- `probe-rs` does not require framming bytes as it only expects `defmt` messages
- `probe-rs` can also read `rtt` messages withouth `defmt` since `rtt` uses two different channel for `rtt` and non-`rtt`.
- `espflash` requires framming bytes as when using `defmt` it also need to prints non-`defmt` messages like the bootloader prints.
- Uses [rzcobs encoding](https://github.com/Dirbaio/rzcobs)

### How to use
1. Enable the `defmt_espflash` feature
1. Select the communication method: `uart`or `jstag-serial`
1. Add the ` "-C", "link-arg=-Tdefmt.x",` `rustflag` in `.cargo/config.toml`
1. Add the `defmt` crate
1. Add `use esp_println as _;` into your `main.rs`
1. Use `defmt::<macro>` to print messages
1. Compile/run setting the log level. Eg: `DEFMT_LOG=debug cargo r`

## [`rtt`](https://wiki.segger.com/RTT)
- RTT works by writing to a buffer in memory and needs a debugger to read the memory from the target.
- Espflash cant do that, you need to use `probe-rs`
- In theory also gdb/openOCD can do it but I think the Espressif forks don't include that functionality

### How to use it
1. Set the proper dependencies/features. Eg:

    defmt = "=0.3.5"
    hal = { package = "esp32c3-hal", version = "0.13.0" }
    esp-backtrace = { version = "0.9.0", features = [
        "esp32c3",
        "exception-handler",
        "panic-handler",
        "print-rtt",
    ] }
    esp-println = { version = "0.7.1", features = [
        "defmt",
        "esp32c3",
        "rtt",
    ], default-features = false }

1. Add the `"-C", "link-arg=-Tdefmt.x",` `rustflag`.
1. Add `use esp_println as _;` on `main.rs`
1. Set runner: `runner = "probe-rs run --chip esp32c3"`
2. Running the code `DEFMT_LOG=debug cargo r` results is:

    ...
     Programming pages   ✔ [00:00:07] [#######################################################################################################################################################] 248.00 KiB/248.00 KiB @ 31.98 KiB/s (eta 0s )    Finished in 12.727s
    WARN  Hello world!
    └─ defmt::__risc_v_rt__main @ src/main.rs:16  
    INFO  Loop...
    └─ defmt::__risc_v_rt__main @ src/main.rs:18  

## `probe-rs`
- By default, uses `defmt`, with any of the [available encodings](https://defmt.ferrous-systems.com/encoding), and `rtt`
- `probe-rs` is not able to read UART or Serial JTAG