"""Sets up the ports."""
self.SPIsetup();
self.MCPreset(); #Reset the chip.
- self.MCPreqstatLoopback();
+
+ # We're going to set some registers, so we must be in config
+ # mode.
+ self.MCPreqstatConfiguration();
+
+ # If we don't enable promiscous mode, we'll miss a lot of
+ # packets. It can be manually disabled later.
+ #self.poke8(0x60,0xFF); #TODO Does this have any unpleasant side effects?
+ self.poke8(0x60,0x66); #Wanted FF, but some bits are reserved.
+
+ #Set the default rate.
+ self.MCPsetrate();
+
+ #Array of supported rates.
+ MCPrates=[83.3, 100, 125,
+ 250, 500, 1000];
+
+ def MCPsetrate(self,rate=125):
+ """Sets the data rate in kHz."""
+ # Now we need to set the timing registers. See chapter 5 of
+ # the MCP2515 datasheet to get some clue as to how this
+ # arithmetic of this works, as my comments here will likely be
+ # rambling, incoherent, and unchanged after I get the infernal
+ # thing working.
+
+ # First, we must chose a Time Quanta (QT) which is used to
+ # define the durations of these segments. Section 5.3
+ # suggests setting BRP<5:0> to 0x04 to get a TQ=500ns, as a 20
+ # MHz crystal gives a clock period of 50ns. This way, for 125
+ # kHz communication, the bit time must be 16 TQ.
+
+ # A bit consists of four parts:
+ # 1: SyncSeg 1 TQ
+ # 2: PropSeg 2 TQ
+ # 3: PhaseSeg1 (PS1) 7 TQ
+ # 4: PhaseSeg2 (PS2) 6 TQ
+
+ # CNF1 with a prescaler of 4 and a SJW of 1 TQ. SJW of 4
+ # might be more stable.
+ #self.poke8(0x2a,0x04);
+
+ # CNF2 with a BLTMODE of 1, SAM of 0, PS1 of 7TQ, and PRSEG of 2TQ
+ #self.poke8(0x29,
+ # 0x80 | # BTLMODE=1
+ # (6<<3) | # 6+1=7TQ for PHSEG1
+ # (1) # 1+1=2TQ for PRSEG
+ # );
+
+ #CNF3 with a PS2 length of 6TQ.
+ #self.poke8(0x28,
+ # 5 #5+1=6TQ
+ # );
+
+
+ print "Setting rate of %i kHz." % rate;
+
+ #These are the new examples.
+ if rate==125:
+ #125 kHz, 16 TQ, not quite as worked out above.
+ CNF1=0x04;
+ CNF2=0xB8;
+ CNF3=0x05;
+ elif rate==100:
+ #100 kHz, 20 TQ
+ CNF1=0x04;
+ CNF2=0xBA;
+ CNF3=0x07;
+ elif rate>83 and rate<83.5:
+ #83+1/3 kHz, 8 TQ
+ # 0.04% error from 83.30
+ CNF1=0x0E;
+ CNF2=0x90;
+ CNF3=0x02;
+ elif rate==250:
+ #256 kHz, 20 TQ
+ CNF1=0x01;
+ CNF2=0xBA;
+ CNF3=0x07;
+ elif rate==500:
+ #500 kHz, 20 TQ
+ CNF1=0x00;
+ CNF2=0xBA;
+ CNF3=0x07;
+ elif rate==1000:
+ #1,000 kHz, 10 TQ
+ CNF1=0x00;
+ CNF2=0xA0;
+ CNF3=0x02;
+ print "WARNING: Because of chip errata, this probably won't work."
+ else:
+ print "Given unsupported rate of %i kHz." % rate;
+ print "Defaulting to 125kHz.";
+ CNF1=0x04;
+ CNF2=0xB8;
+ CNF3=0x05;
+ self.poke8(0x2a,CNF1);
+ self.poke8(0x29,CNF2);
+ self.poke8(0x28,CNF3);
+
def MCPreset(self):
"""Reset the MCP2515 chip."""
self.SPItrans([0xC0]);
0x00, 0x00, 0x00, 0x00
]);
return data[1:len(data)];
+ def writetxbuffer(self,packet,packbuf=0):
+ """Writes the transmit buffer."""
+ self.SPItrans([0x40|(packbuf<<1)]+packet);
+
def rxpacket(self):
"""Reads the next incoming packet from either buffer.
Returns None immediately if no packet is waiting."""
status=self.MCPrxstatus()&0xC0;
if status&0x40:
#Buffer 0 has higher priority.
- return self.rxbuffer(0);
+ return self.readrxbuffer(0);
elif status&0x80:
#Buffer 1 has lower priority.
- return self.rxbuffer(1);
+ return self.readrxbuffer(1);
else:
return None;
+ def txpacket(self,packet):
+ """Transmits a packet through one of the outbound buffers.
+ As usual, the packet should begin with SIDH.
+ For now, only TXB0 is supported."""
+ self.writetxbuffer(packet,0);
+ self.MCPrts(TXB0=True);
def packet2str(self,packet):
"""Converts a packet from the internal format to a string."""
toprint="";
def poke8(self,adr,val):
"""Poke a value into RAM. Untested"""
self.SPItrans([0x02,adr&0xFF,val&0xFF]);
+ newval=self.peek8(adr);
+ if newval!=val:
+ print "Failed to poke %02x to %02x. Got %02x." % (adr,val,newval);
+ print "Are you not in idle mode?";
return val;
projects / goodfet / blobdiff