from GoodFETSPI import GoodFETSPI;
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?
+
+ # 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
+ );
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]);
return ord(data[1]);
+
def MCPreadstatus(self):
"""Reads the Read Status by the SPI verb of the same name."""
#See page 67 of the datasheet for the flag names.
data=self.SPItrans([0xA0,0x00]);
return ord(data[1]);
+
def MCPrts(self,TXB0=False,TXB1=False,TXB2=False):
"""Requests to send one of the transmit buffers."""
flags=0;
if flags==0:
print "Warning: Requesting to send no buffer.";
- """Request To Send a transmission."""
self.SPItrans([0x80|flags]);
+ def readrxbuffer(self,packbuf=0):
+ """Reads the RX buffer. Might have old data."""
+ data=self.SPItrans([0x90|(packbuf<<2),
+ 0x00,0x00, #SID
+ 0x00,0x00, #EID
+ 0x00, #DLC
+ 0x00, 0x00, 0x00, 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.readrxbuffer(0);
+ elif status&0x80:
+ #Buffer 1 has lower priority.
+ 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="";
+ for bar in packet:
+ toprint=toprint+("%02x "%ord(bar))
+ return toprint;
def peek8(self,adr):
"""Read a byte from the given address. Untested."""
data=self.SPItrans([0x03,adr&0xFF,00]);
return ord(data[2]);
-
+ def MCPbitmodify(self,adr,mask,data):
+ """Writes a byte with a mask. Doesn't work for many registers."""
+ data=self.SPItrans([0x05,adr&0xFF,mask&0xFF,data&0xFF]);
+ return ord(data[2]);
def poke8(self,adr,val):
"""Poke a value into RAM. Untested"""
self.SPItrans([0x02,adr&0xFF,val&0xFF]);