class GoodFETMCPCAN(GoodFETSPI):
"""This class uses the regular SPI app to implement a CAN Bus
adapter on the Goodthopter10 hardware."""
-
+ MCPMODES=["Normal","Sleep","Loopback","Listen-only","Configuration",
+ "UNKNOWN","UNKNOWN","PowerUp"];
def MCPsetup(self):
"""Sets up the ports."""
self.SPIsetup();
self.MCPreset(); #Reset the chip.
+ # 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?
+
+ #Set the default rate of 125kHz.
+ self.MCPsetrate(125);
+
+ 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
+ # );
+
+
+ #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==500:
+ #500 kHz, 20 TQ
+ CNF1=0x00;
+ CNF2=0xBA;
+ CNF3=0x07;
+ pass;
+ elif rate==100:
+ #100 kHz, 20 TQ
+ CNF1=0x04;
+ CNF2=0xBA;
+ CNF3=0x07;
+ pass;
+ 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.";
+ 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]);
-
+ def MCPcanstat(self):
+ """Get the CAN Status."""
+ return self.peek8(0x0E);
+ def MCPreqstatNormal(self):
+ """Set the CAN state."""
+ state=0x0;
+ self.MCPbitmodify(0x0F,0xE0,(state<<5));
+ def MCPreqstatSleep(self):
+ """Set the CAN state."""
+ state=0x1;
+ self.MCPbitmodify(0x0F,0xE0,(state<<5));
+ def MCPreqstatLoopback(self):
+ """Set the CAN state."""
+ state=0x2;
+ self.MCPbitmodify(0x0F,0xE0,(state<<5));
+ def MCPreqstatListenOnly(self):
+ """Set the CAN state."""
+ state=0x3;
+ self.MCPbitmodify(0x0F,0xE0,(state<<5));
+ def MCPreqstatConfiguration(self):
+ """Set the CAN state."""
+ state=0x4;
+ self.MCPbitmodify(0x0F,0xE0,(state<<5));
+
+ def MCPcanstatstr(self):
+ """Read the present status as a string."""
+ status=self.MCPcanstat();
+ opmod=(status&0xE0)>>5;
+ return self.MCPMODES[opmod];
def MCPrxstatus(self):
"""Reads the RX Status by the SPI verb of the same name."""
data=self.SPItrans([0xB0,0x00]);
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="";
projects / goodfet / blobdiff