PARTIAL work towards GDB interface.

TODO: dispatch functions should afftect the simulator.
TODO: Fill in test stubs.
TODO: Document.
Fixes #17.

revelation/gdb/breakpoints.py

@@ -0,0 +1,46 @@
+from revelation.isa import decode
+
+BKPT16 = 0b0000000111000010
+NOP16 = 0b0000000110100010
+
+
+class BreakPointManager(object):
+    """Manage breakpoints during GDB execution.
+    """
+
+    def __init__(self, simulator):
+        self.target = simulator
+        self.breakpoints = {}  # Address -> (opcode, size in bytes)
+
+    def _get_global_address(self, address, coreid=0x808):
+        """Remap any local addresses to global address.
+        """
+        if (address >> 20) == 0x0:
+            return (coreid << 20) | address
+        return address
+
+    def is_breakpoint_set(self, address):
+        return address in self.breakpoints
+
+    def set_breakpoint(self, address, coreid=0x080):
+        """Set a breakpoint at a given address.
+        1. Read 32 bit current instructions at address, save in dictionary.
+        2. If current instruction is 16 bit, replace with bkpt16.
+        3. If current instruction is 32 bit, replace with bkpt16, nop16.
+        """
+        global_address = self._get_global_address(address, coreid)
+        opcode = self.target.memory.iread(global_address, 4)
+        mnemonic, _ = decode(opcode)
+        if mnemonic.endswith('16'):
+            self.breakpoints[global_address] = (opcode & 0xffff, 2)
+            self.target.memory.write(global_address, 2, BKPT16)
+        else:
+            self.breakpoints[global_address] = (opcode, 4)
+            self.target.memory.write(global_address, 2, BKPT16)
+            self.target.memory.write(global_address + 2, 2, NOP16)
+
+    def remove_breakpoint(self, address, coreid=0x808):
+        """Remove a breakpoint at a given address."""
+        global_address = self._get_global_address(address, coreid)
+        opcode, size = self.breakpoints[global_address]
+        self.target.memory.write(global_address, size, opcode)