Source code for cocotb.drivers.opb

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"""
Drivers for On-chip Peripheral Bus.

NOTE: Currently we only support a very small subset of functionality.
"""

import cocotb
from cocotb.triggers import RisingEdge, ReadOnly, Event
from cocotb.drivers import BusDriver
from cocotb.result import ReturnValue


class OPBException(Exception):
    pass


[docs]class OPBMaster(BusDriver): """On-chip peripheral bus master.""" _signals = ["xferAck", "errAck", "toutSup", "retry", "DBus_out", "select", "RNW", "BE", "ABus", "DBus_in"] _optional_signals = ["seqAddr"] _max_cycles = 16 def __init__(self, entity, name, clock, **kwargs): BusDriver.__init__(self, entity, name, clock, **kwargs) self.bus.select.setimmediatevalue(0) self.log.debug("OPBMaster created") self.busy_event = Event("%s_busy" % name) self.busy = False @cocotb.coroutine def _acquire_lock(self): if self.busy: yield self.busy_event.wait() self.busy_event.clear() self.busy = True def _release_lock(self): self.busy = False self.busy_event.set()
[docs] @cocotb.coroutine def read(self, address, sync=True): """Issue a request to the bus and block until this comes back. Simulation time still progresses but syntactically it blocks. Args: address (int): The address to read from. sync (bool, optional): Wait for rising edge on clock initially. Defaults to True. Returns: BinaryValue: The read data value. Raises: OPBException: If read took longer than 16 cycles. """ yield self._acquire_lock() # Apply values for next clock edge if sync: yield RisingEdge(self.clock) self.bus.ABus <= address self.bus.select <= 1 self.bus.RNW <= 1 self.bus.BE <= 0xF count = 0 while not int(self.bus.xferAck.value): yield RisingEdge(self.clock) yield ReadOnly() if int(self.bus.toutSup.value): count = 0 else: count += 1 if count >= self._max_cycles: raise OPBException("Read took longer than 16 cycles") data = int(self.bus.DBus_out.value) # Deassert read self.bus.select <= 0 self._release_lock() self.log.info("Read of address 0x%x returned 0x%08x" % (address, data)) raise ReturnValue(data)
[docs] @cocotb.coroutine def write(self, address, value, sync=True): """Issue a write to the given address with the specified value. Args: address (int): The address to read from. value (int): The data value to write. sync (bool, optional): Wait for rising edge on clock initially. Defaults to True. Raises: OPBException: If write took longer than 16 cycles. """ yield self._acquire_lock() if sync: yield RisingEdge(self.clock) self.bus.ABus <= address self.bus.select <= 1 self.bus.RNW <= 0 self.bus.BE <= 0xF self.bus.DBus_out <= value count = 0 while not int(self.bus.xferAck.value): yield RisingEdge(self.clock) yield ReadOnly() if int(self.bus.toutSup.value): count = 0 else: count += 1 if count >= self._max_cycles: raise OPBException("Write took longer than 16 cycles") self.bus.select <= 0 self._release_lock()