add command to reboot into DFU

Co-Authored-By: topquark12 <aw@m-labs.hk>
Co-Committed-By: topquark12 <aw@m-labs.hk>

README.md

@@ -124,6 +124,7 @@ formatted as line-delimited JSON.
 | `load [0/1]`                     | Restore configuration for channel all/0/1 from flash                 |
 | `save [0/1]`                     | Save configuration for channel all/0/1 to flash                      |
 | `reset`                          | Reset the device                                                     |
+| `dfu`                            | Reset device and enters USB device firmware update (DFU) mode |
 | `ipv4 <X.X.X.X/L> [Y.Y.Y.Y]`     | Configure IPv4 address, netmask length, and optional default gateway |
 
 

memory.x

@@ -3,10 +3,13 @@ MEMORY
   FLASH (rx)      : ORIGIN = 0x8000000, LENGTH = 1024K
   /* reserved for config data */
   CONFIG (rx)     : ORIGIN = 0x8100000, LENGTH = 16K
-  RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 112K
+  RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 112K - 4
+  /* reserved for DFU trigger message */
+  DFU_MSG (wrx)   : ORIGIN = 0x2001BFFC, LENGTH = 4
   RAM2 (xrw)      : ORIGIN = 0x2001C000, LENGTH = 16K
   RAM3 (xrw)      : ORIGIN = 0x20020000, LENGTH = 64K
   CCMRAM (rw)     : ORIGIN = 0x10000000, LENGTH = 64K
 }
 
 _stack_start = ORIGIN(CCMRAM) + LENGTH(CCMRAM);
+_dfu_msg = ORIGIN(DFU_MSG);

src/command_parser.rs

@@ -179,6 +179,7 @@ pub enum Command {
         channel: usize,
         rate: Option<f32>,
     },
+    Dfu,
 }
 
 fn end(input: &[u8]) -> IResult<&[u8], ()> {
@@ -535,6 +536,7 @@ fn command(input: &[u8]) -> IResult<&[u8], Result<Command, Error>> {
          pid,
          steinhart_hart,
          postfilter,
+         value(Ok(Command::Dfu), tag("dfu")),
     ))(input)
 }
 

src/dfu.rs

@@ -0,0 +1,49 @@
+use cortex_m_rt::{pre_init};
+
+const DFU_TRIG_MSG: u32 = 0xDECAFBAD;
+
+extern "C" {
+    // This symbol comes from memory.x
+    static mut _dfu_msg: u32;
+}
+
+pub unsafe fn set_dfu_trigger() {
+    _dfu_msg = DFU_TRIG_MSG;
+}
+
+/// Called by reset handler in lib.rs immediately after reset.
+/// This function should not be called outside of reset handler as 
+/// bootloader expects MCU to be in reset state when called.
+#[pre_init]
+unsafe fn __pre_init() {
+    if _dfu_msg == DFU_TRIG_MSG {
+        _dfu_msg = 0x00000000;
+
+        // Enable system config controller clock
+        const RCC_APB2ENR: *mut u32 = 0xE000_ED88 as *mut u32;
+        const RCC_APB2ENR_ENABLE_SYSCFG_CLOCK: u32 = 0x00004000;
+
+        core::ptr::write_volatile(
+            RCC_APB2ENR,
+            *RCC_APB2ENR | RCC_APB2ENR_ENABLE_SYSCFG_CLOCK,
+        );
+
+        // Bypass BOOT pins and remap bootloader to 0x00000000
+        const SYSCFG_MEMRMP: *mut u32 = 0x40013800 as *mut u32;
+        const SYSCFG_MEMRMP_MAP_ROM: u32 = 0x00000001;
+
+        core::ptr::write_volatile(
+            SYSCFG_MEMRMP,
+            *SYSCFG_MEMRMP | SYSCFG_MEMRMP_MAP_ROM,
+        );
+        
+        asm!(
+            // Set stack pointer to bootloader location
+            "LDR R0, =0x1FFF0000",
+            "LDR SP,[R0, #0]",
+            // Jump to bootloader
+            "LDR R0,[R0, #4]",
+            "BX R0",
+        );
+    }
+}

src/main.rs

@@ -1,6 +1,6 @@
 #![cfg_attr(not(test), no_std)]
 #![cfg_attr(not(test), no_main)]
-#![feature(maybe_uninit_extra, maybe_uninit_ref)]
+#![feature(maybe_uninit_extra, maybe_uninit_ref, asm)]
 #![cfg_attr(test, allow(unused))]
 // TODO: #![deny(warnings, unused)]
 
@@ -66,6 +66,7 @@ mod channel_state;
 mod config;
 use config::ChannelConfig;
 mod flash_store;
+mod dfu;
 
 const HSE: MegaHertz = MegaHertz(8);
 #[cfg(not(feature = "semihosting"))]
@@ -77,7 +78,6 @@ const CHANNEL_CONFIG_KEY: [&str; 2] = ["ch0", "ch1"];
 
 const TCP_PORT: u16 = 23;
 
-
 fn send_line(socket: &mut TcpSocket, data: &[u8]) -> bool {
     let send_free = socket.send_capacity() - socket.send_queue();
     if data.len() > send_free + 1 {
@@ -422,6 +422,16 @@ fn main() -> ! {
                                         channels.power_down(i);
                                     }
 
+                                    SCB::sys_reset();
+                                }
+                                Command::Dfu => {
+                                    for i in 0..CHANNELS {
+                                        channels.power_down(i);
+                                    }
+                                    unsafe {
+                                        dfu::set_dfu_trigger();
+                                    }
+                                    
                                     SCB::sys_reset();
                                 }
                             }