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125 lines
3.2 KiB
Python
125 lines
3.2 KiB
Python
#!/usr/bin/python
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"""
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Emulate the imlac Paper Tape Reader (PTR).
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We take some pains to closely emulate the *real* PTR device, even
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including misuse, such as no tape mounted. This means we must tell
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the PTR object how many CPU cycles have passed (tick()).
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"""
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from Globals import *
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class Ptr(object):
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# number of chars per second we want
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CharsPerSecond = 300
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# duty cycle for PTR is 30% ready and 70% not ready
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ReadyCycles = int((CYCLES_PER_SECOND / CharsPerSecond) / 0.7) / 25
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NotReadyCycles = int((CYCLES_PER_SECOND / CharsPerSecond) / 0.3) / 25
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# no tape in reader, return 0377 (all holes see light)
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PtrEOF = 0377
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# module-level state variables
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motor_on = False
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device_ready = False
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open_file = None
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filename = None
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at_eof = True
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value = PtrEOF
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cycle_count = 0
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def __init__(self):
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"""Initialize the paertape reader device."""
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self.motor_on = False
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self.device_ready = False
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self.open_file = None
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self.filename = None
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self.at_eof = True
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self.value = self.PtrEOF
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self.cycle_count = 0
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def mount(self, fname):
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"""Mount papertape file on the reader device."""
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self.motor_on = False
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self.device_ready = False
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self.cycle_count = self.NotReadyCycles
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self.filename = fname
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self.open_file = open(self.filename, 'rb')
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self.at_eof = False
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self.value = None
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def dismount(self):
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"""Dismount a papertape file."""
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self.motor_on = False
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self.device_ready = False
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if self.filename:
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self.open_file.close()
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self.open_file = None
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self.filename = None
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self.at_eof = True
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self.value = self.PtrEOF
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def start(self):
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"""Turn papertape reader motor on."""
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self.motor_on = True
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self.device_ready = False
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self.cycle_count = self.ReadyCycles
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def stop(self):
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"""Stop reader motor."""
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self.motor_on = False
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self.device_ready = False
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self.cycle_count = self.ReadyCycles
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def read(self):
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"""Read papertape value."""
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return self.value
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def eof(self):
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"""Return reader EOF status."""
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return self.at_eof
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def tick(self, cycles):
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"""Called to push PTR state along.
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cycles number of cycles passed since last tick
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"""
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# if end of tape or motor off, do nothing, state remains unchanged
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if self.at_eof or not self.motor_on:
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return
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self.cycle_count -= cycles
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if self.cycle_count <= 0:
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if self.device_ready:
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self.device_ready = False
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self.cycle_count += self.NotReadyCycles
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else:
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self.device_ready = True
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self.cycle_count += self.ReadyCycles
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self.value = self.open_file.read(1)
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if len(self.value) < 1:
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# EOF on input file, pretend end of tape
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self.at_eof = True
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self.value = self.PtrEOF
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else:
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self.value = ord(self.value)
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def ready(self):
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"""Test if reader is ready."""
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return self.device_ready
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