fix(serial): Perform serial prints in a critical section

Sometimes during initialization, one `log_msg()` intercepts another one,
leading to a whole lot of weird issues in other modules (like I2C).  I
suspect this to be memory corruption of some kind.  The issues can be
fixed by performing serial prints in a critical section, thus ensuring
atomicity of prints.  Note that this does not mean log messages will not
interleave.

The CDC-ACM and BLE-Serial writes cannot be put into a critical section
and are thus a point where this code can still fail.  For now, however,
this fix ensures the race-conditions during startup, where USB and BLE
are not yet running, don't happen anymore.

Signed-off-by: Rahix <rahix@rahix.de>

epicardium/modules/serial.c

@@ -27,7 +27,21 @@ static QueueHandle_t read_queue;
  */
 void epic_uart_write_str(const char *str, intptr_t length)
 {
+	uint32_t basepri = __get_BASEPRI();
+	if (xPortIsInsideInterrupt()) {
+		taskENTER_CRITICAL_FROM_ISR();
+	} else {
+		taskENTER_CRITICAL();
+	}
+
 	UART_Write(ConsoleUart, (uint8_t *)str, length);
+
+	if (xPortIsInsideInterrupt()) {
+		taskEXIT_CRITICAL_FROM_ISR(basepri);
+	} else {
+		taskEXIT_CRITICAL();
+	}
+
 	cdcacm_write((uint8_t *)str, length);
 	ble_uart_write((uint8_t *)str, length);
 }