platforms/stm32f7: add reusable F722 firmware

platforms/stm32f7/src/f722/diagnostics.rs

@@ -0,0 +1,59 @@
+//! Focused physical-route diagnostics for supported F722 boards.
+
+use super::peripherals::{Usart2Tx, configure_usart2_pins_pa2_pa3, select_pll216_profile};
+use cortex_m_rt as _;
+use panic_halt as _;
+use stm32f7::stm32f722;
+
+const UART2_CLOCK_HZ: u32 = 54_000_000;
+const UART2_BAUD: u32 = 115_200;
+const SQUARE_WAVE_BYTE: u8 = 0x55;
+const LED_TOGGLE_INTERVAL_BYTES: u16 = 11_520;
+
+/// Continuously transmits `0x55` on the GEP-F722-HD V2's T2 pad.
+///
+/// This intentionally initializes only the clock tree, PA2/PA3, and USART2.
+/// It does not enable RTIC, DMA, MAVLink, sensors, timers, or motor outputs.
+/// The PA13 blue LED also changes state roughly once per second, proving the
+/// test passed clock and UART initialization. A host at 115200 8N1 must
+/// receive a continuous sequence of `55` bytes.
+pub fn geprc_uart2_wire_test() -> ! {
+    // SAFETY: this diagnostic installs the sole reset entry point and takes no
+    // interrupt or RTIC path, so no other code can own these peripherals.
+    let device = unsafe { stm32f722::Peripherals::steal() };
+
+    select_pll216_profile(&device.RCC, &device.PWR, &device.FLASH)
+        .expect("could not select F722 PLL216 clock profile");
+    device
+        .RCC
+        .ahb1enr()
+        .modify(|_, write| write.gpioaen().set_bit());
+    configure_usart2_pins_pa2_pa3(&device.GPIOA);
+    device
+        .GPIOA
+        .moder()
+        .modify(|_, write| write.moder13().output());
+    // The V2's blue LED is active low. Start it off so each following toggle
+    // is visible; PA13 is otherwise unused by this standalone diagnostic.
+    device.GPIOA.bsrr().write(|write| write.bs13().set_bit());
+    let uart = Usart2Tx::new(&device.RCC, device.USART2, UART2_CLOCK_HZ, UART2_BAUD)
+        .expect("could not initialize USART2");
+
+    let mut bytes_since_led_toggle = 0;
+    let mut led_is_on = false;
+    loop {
+        uart.write_blocking(SQUARE_WAVE_BYTE);
+        bytes_since_led_toggle += 1;
+        if bytes_since_led_toggle == LED_TOGGLE_INTERVAL_BYTES {
+            bytes_since_led_toggle = 0;
+            led_is_on = !led_is_on;
+            device.GPIOA.bsrr().write(|write| {
+                if led_is_on {
+                    write.br13().set_bit()
+                } else {
+                    write.bs13().set_bit()
+                }
+            });
+        }
+    }
+}