first pass at syscall interface

kernel/src/syscall.rs

@@ -19,3 +19,25 @@ pub enum Syscall {
     /// Various memory operations.
     MEMOP = 4,
 }
+
+/// This trait must be implemented by the architecture of the chip Tock is
+/// running on. It allows the kernel to manage processes in an
+/// architecture-agnostic manner.
+pub trait SyscallInterface {
+    /// Allows the kernel to query the architecture to see if a syscall occurred
+    /// for the currently running process.
+    fn get_syscall_fired(&self) -> bool;
+
+    /// Get the syscall that the process called.
+    fn get_syscall_number(&self, stack_pointer: *const u8) -> Option<Syscall>;
+
+    /// Get the four u32 values that the process can pass with the syscall.
+    fn get_syscall_data(&self, stack_pointer: *const u8) -> (u32, u32, u32, u32);
+
+    /// Replace the last stack frame with the new function call. This function
+    /// is what should be executed when the process is resumed.
+    fn replace_function_call(&self, stack_pointer: *const u8, callback: FunctionCall);
+
+    /// Context switch to a specific process.
+    fn switch_to_process(&self, stack_pointer: *const u8) -> *mut u8;
+}