Merge pull request adafruit#95 from mpratt14/patch-2

ladyada · web-flow · commit 0ec1977df23c · 2019-03-28T23:58:46.000-04:00
Add SPI method: bulkread
diff --git a/Adafruit_GPIO/FT232H.py b/Adafruit_GPIO/FT232H.py
@@ -504,6 +504,51 @@ def read(self, length):
         self._deassert_cs()
         # Read response bytes.
         return bytearray(self._ft232h._poll_read(length))
+    
+    def bulkread(self, data = [], lengthR = 'None', readmode = 1):
+        """Half-duplex SPI write then read. Send command and payload to slave as bytearray
+            then consequently read out response from the slave for length in bytes.
+        Designed for use with NOR or NAND flash chips, and possibly SD cards...etc...
+        Read command is cut in half and performed twice in series to prevent single byte errors.
+        Hardware limits per command are enforced before doing anything.
+        Read length is an optional argument, so that it can function similar to transfer
+            but still half-duplex.
+        For reading without writing, one can send a blank array or skip that argument.
+        """
+        #check for hardware limit of FT232H and similar MPSSE chips
+        if (1 > lengthR > 65536)|(len(data) > 65536):
+            print 'the FTDI chip is limited to 65536 bytes (64 KB) of input/output per command!'
+            print 'use for loops for larger reads'
+            exit(1)
+        #default mode is to act like `transfer` but half-duplex
+        if (lengthR == 'None')&(readmode == 1):
+            lengthR = len(data)
+        #command parameters definition and math
+        #MPSSE engine sees length 0 as 1 byte, so - 1 lengths
+        commandW = 0x10 | (spi.lsbfirst << 3) | spi.write_clock_ve
+        lengthW = len(data) - 1
+        len_lowW  = (lengthW) & 0xFF
+        len_highW = ((lengthW) >> 8) & 0xFF
+        commandR = 0x20 | (spi.lsbfirst << 3) | (spi.read_clock_ve << 2)
+        lengthR = lengthR/2
+        len_lowR  = (lengthR-1) & 0xFF
+        len_highR = ((lengthR-1) >> 8) & 0xFF
+        #logger debug info
+        #logger.debug('SPI bulkread with write command {0:2X}.'.format(commandW))
+        #logger.debug('and read command {0:2X}.'.format(commandR))
+        #begin command set
+        spi._assert_cs()
+        #write command, these have to be separated due to TypeError
+        spi._ft232h._write(str(bytearray((commandW, len_lowW, len_highW))))
+        spi._ft232h._write(str(bytearray(data)))
+        #read command, which is now divided into two commands
+        spi._ft232h._write(str(bytearray((commandR, len_lowR, len_highR))))
+        payload1 = spi._ft232h._poll_read(lengthR)
+        spi._ft232h._write(str(bytearray((commandR, len_lowR, len_highR))))
+        payload2 = spi._ft232h._poll_read(lengthR)
+        #end command set
+        spi._deassert_cs()
+        return bytearray(payload1 + payload2)
 
     def transfer(self, data):
         """Full-duplex SPI read and write.  The specified array of bytes will be
