Reverted some CCSPI performance patches. This might slow down the Z1.

[goodfet] / client / GoodFETMCPCAN.py

diff --git a/client/GoodFETMCPCAN.py b/client/GoodFETMCPCAN.py
index 4270b20..0441ecb 100644 (file)
--- a/client/GoodFETMCPCAN.py
+++ b/client/GoodFETMCPCAN.py
@@ -23,7 +23,48 @@ class GoodFETMCPCAN(GoodFETSPI):
         """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?
+        
+        # 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]);
@@ -88,18 +129,28 @@ class GoodFETMCPCAN(GoodFETSPI):
                        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="";