Remove OS from build.

Also update instructions so user flashes OS separately.

Author: thejpster

README.md

@@ -82,65 +82,56 @@ Currently the BIOS uses Core 0 for running the Neotron OS (and application code)
 
 The Neotron BIOS uses the [defmt](https://crates.io/crates/defmt) crate to provide structured logging over the SWD interface. The easiest way to flash and debug your Neotron Pico BIOS is with a second Raspberry Pi Pico, or the official Raspberry Pi Debug Probe.
 
-1. If your BMC has not been programmed, do that first.
+1. If your BMC has not been programmed, [do that first](https://github.com/Neotron-Compute/Neotron-BMC/blob/v0.5.2/neotron-bmc-pico/README.md).
 
-2. Connect your *Debugger* Pico to the three *DEBUG* pins on the *Neotron* Pico, following the instructions for your particular debugging device or firmware.
+1. Connect your *Debug Probe* to the three *DEBUG* pins on the *Raspberry Pi Pico* fitted to your Neotron Pico, following the instructions for your particular debugging device or firmware.
 
-3. If your *Debugger* Pico was a bare Pi Pico (and not a Debug Probe) then flash it with <https://github.com/raspberrypi/picoprobe> or <https://github.com/majbthrd/DapperMime> firmware (e.g. by copying the UF2 file to the USB Mass Storage device)
+1. On your PC, install the [*probe-rs*](https://github.com/probe-rs), a microcontroller flashing tool. See website for instructions.
 
-4. On your PC, install [*probe-rs*](https://github.com/probe-rs), a microcontroller flashing tool.
+1. Power on your Neotron Pico into bootloader mode by applying 12V, holding down
+   the "BOOTSEL" button on the Raspberry Pi Pico and then and tapping the On/Off
+   button on the Neotron.
 
-   ```sh
-   cargo install probe-rs --features=cli
-   ```
+   If you don't put the Raspberry Pi Pico into bootloader mode then when
+   `probe-rs` resets the chip after programming, the firmware will detect it has
+   had an incomplete reset and cause a full reset. This makes the video output
+   more reliable, but the full reset will immediately disconnect `probe-rs` so
+   you won't see any log messages. Booting the RP2040 in USB bootloader mode
+   avoids this issue by making the `probe-rs` triggered reset look more like a
+   full reset.
 
-5. Build the Neotron OS:
-    We use the "neotron-flash-1002.ld" linker script to link it at `0x1002_0000`.
+1. Flash the BIOS.
 
-    ```console
-    user@host ~/neotron-os $ cargo build --bin=flash1002 --release --target=thumbv6m-none-eabi
-    user@host ~/neotron-os $ arm-none-eabi-objcopy -O binary ./target/thumbv6m-none-eabi/release/flash1002 ../neotron-pico-bios/src/thumbv6m-none-eabi-flash1002-libneotron_os.bin
-    ```
+    1. You can compile from source and flash all-in-one:
 
-6. Power on your Neotron Pico into bootloader mode by applying 12V, holding down
-   the "BOOTSEL" button on the Raspberry Pi Pico and then and tapping the On/Off
-   button on the Neotron.
+        ```bash
+        cargo run --release
+        ```
 
-   If you don't put the RP2040 into bootloader mode then when `probe-rs` resets
-   the chip after programming, the firmware will detect it has had an incomplete
-   reset and cause a full reset. This makes the video output more reliable, but
-   the full reset will immediately disconnect `probe-rs` so you won't see any
-   log messages. Booting the RP2040 in USB bootloader mode avoids this issue by
-   making the `probe-rs` triggered reset look more like a full reset.
-
-7. Build and load the Neotron BIOS, and view the debug output stream, with `cargo run --release`.
-
-    ```console
-    user@host ~/neotron-pico-bios $ DEFMT_LOG=debug cargo run --release
-      Compiling neotron-pico-bios v0.1.0 (/home/jonathan/Documents/neotron/neotron-pico-bios)
-        Finished release [optimized + debuginfo] target(s) in 0.76s
-        Running `probe-rs run --chip RP2040 target/thumbv6m-none-eabi/release/neotron-pico-bios`
-    (HOST) INFO  flashing program (7.30 KiB)
-    (HOST) INFO  success!
-    ────────────────────────────────────────────────────────────────────────────────
-    INFO  Neotron BIOS starting...
-    └─ neotron_pico_bios::__cortex_m_rt_main @ src/main.rs:79
-    INFO  Clocks OK
-    └─ neotron_pico_bios::__cortex_m_rt_main @ src/main.rs:102
-    INFO  Pins OK
-    └─ neotron_pico_bios::__cortex_m_rt_main @ src/main.rs:121
-    DEBUG Loop...
-    └─ neotron_pico_bios::__cortex_m_rt_main @ src/main.rs:128
-    ```
-
-    You should see your Neotron Pico boot, both over RTT in the `probe-rs` output, and also on the VGA output.
+    1. You can download the `neotron-pico-bios.elf` file from [Github
+    Releases](https://github.com/Neotron-Compute/Neotron-Pico-BIOS/releases) and
+    flash with `probe-rs`:
+
+        ```bash
+        probe-rs run --chip RP2040 ~/Downloads/neotron-pico-bios
+        ```
+
+    1. You can download the `neotron-pico-bios.uf2` file from [Github
+    Releases](https://github.com/Neotron-Compute/Neotron-Pico-BIOS/releases) and
+    flash by copying to the RP2040 bootloader's fake USB Mass Storage Device. You will need to connect a USB cable to the Raspberry Pi Pico's external USB micro-AB port, and ensure that the USB Host Power jumper near the 12V input is NOT fitted.
+
+1. Now when you reset your board, you will see the BIOS splash screen on any
+   connected VGA display and some start-up tones on any connected PC Speaker. No
+   OS will be booted, as we haven't flashed the OS yet. Grab a compatible OS
+   release from <https://github.com/Neotron-Compute/Neotron-OS/releases>. You
+   need the `flash1002` variant for the Neotron Pico, because the BIOS expects
+   the OS to live in flash at address `0x1002_0000`.
 
 ## Multiple Probes
 
 If you have multiple `probe-rs` compatible probes attached to your computer,
 you will receive an error message.
 
-
 You will need to check what probes are available and edit `.cargo/config.toml` to add the appropriate `--probe VID:PID` argument.
 
 ```console
@@ -165,7 +156,7 @@ See [CHANGELOG.md](./CHANGELOG.md)
 ## Licence
 
 ```text
-Neotron-Pico-BIOS Copyright (c) Jonathan 'theJPster' Pallant and the Neotron Developers, 2023
+Neotron-Pico-BIOS Copyright (c) Jonathan 'theJPster' Pallant and the Neotron Developers, 2024
 
 This program is free software: you can redistribute it and/or modify
 it under the terms of the GNU General Public License as published by

src/main.rs

@@ -14,7 +14,7 @@
 // -----------------------------------------------------------------------------
 // Licence Statement
 // -----------------------------------------------------------------------------
-// Copyright (c) Jonathan 'theJPster' Pallant and the Neotron Developers, 2023
+// Copyright (c) Jonathan 'theJPster' Pallant and the Neotron Developers, 2024
 //
 // This program is free software: you can redistribute it and/or modify it under
 // the terms of the GNU General Public License as published by the Free Software
@@ -64,6 +64,7 @@ use core::{
 	fmt::Write,
 	ptr::{addr_of, addr_of_mut},
 	sync::atomic::{AtomicBool, AtomicU32, Ordering},
+	u32,
 };
 
 // Third Party Stuff
@@ -256,17 +257,6 @@ static HARDWARE: NeoMutex<Option<Hardware>> = NeoMutex::new(None);
 /// The pin we use for external interrupt input
 static IRQ_PIN: NeoMutex<Option<IrqPin>> = NeoMutex::new(None);
 
-/// This is our Operating System. It must be compiled separately.
-///
-/// The RP2040 requires an OS linked at `0x1002_0000` and compiled for the
-/// `thumbv6m-none-eabi` target. You should therefore use the binary
-/// `thumbv6m-none-eabi-flash1002-libneotron_os.bin` from
-/// <https://github.com/Neotron-Compute/Neotron-OS/releases>
-#[link_section = ".flash_os"]
-#[used]
-pub static OS_IMAGE: [u8; include_bytes!("thumbv6m-none-eabi-flash1002-libneotron_os.bin").len()] =
-	*include_bytes!("thumbv6m-none-eabi-flash1002-libneotron_os.bin");
-
 /// Tracks if we have had an IO interrupt.
 ///
 /// Set by the GPIO interrupt routine to reflect the level state of the IRQ input
@@ -526,8 +516,22 @@ fn main() -> ! {
 	sign_on();
 
 	// Now jump to the OS
-	let code: &common::OsStartFn = unsafe { ::core::mem::transmute(&_flash_os_start) };
-	code(&API_CALLS);
+	unsafe {
+		let entry_fn_addr: *const usize = addr_of!(_flash_os_start) as *const usize;
+		info!("entry_fn_addr = 0x{:08x}", entry_fn_addr);
+		let entry_fn = entry_fn_addr.read_volatile();
+		info!("entry_fn = 0x{:08x}", entry_fn);
+		if entry_fn != 0xFFFF_FFFF && entry_fn != 0x0000_0000 {
+			// looks like it's not blank at least - let's jump to it
+			let code: common::OsStartFn = core::mem::transmute(entry_fn);
+			code(&API_CALLS);
+		} else {
+			// flash looks blank - sit at the splash screen
+			loop {
+				cortex_m::asm::wfe();
+			}
+		}
+	}
 }
 
 /// Check if the rest of the system appears to be running already.
@@ -583,7 +587,7 @@ fn sign_on() {
 	static LOGO_ANSI_BYTES: &[u8] = include_bytes!(concat!(env!("OUT_DIR"), "/logo.bytes"));
 	static COPYRIGHT_TEXT: &str = "\
 		\n\
-		Copyright © Jonathan 'theJPster' Pallant and the Neotron Developers, 2023\n\
+		Copyright © Jonathan 'theJPster' Pallant and the Neotron Developers, 2024\n\
 		This program is free software under GPL v3 (or later)\n\
 		You are entitled to the Complete and Corresponding Source for this BIOS\n\
 		\n\
@@ -702,6 +706,8 @@ fn sign_on() {
 			countdown -= 1;
 		}
 	}
+
+	write!(&tc, "Now starting OS (if present)...").unwrap();
 }
 
 /// Paint the Core 0 and Core 1 stacks