SPI handle in python lib (#1131)

* SPI handle in python lib

* add spidev

* unify those

* clean up connect

* clean that up

Co-authored-by: Robbe Derks <robbe.derks@gmail.com>

python/spi.py

@@ -0,0 +1,74 @@
+import struct
+import spidev
+from functools import reduce
+
+# Constants
+SYNC = 0x5A
+HACK = 0x79
+DACK = 0x85
+NACK = 0x1F
+CHECKSUM_START = 0xAB
+
+MAX_RETRY_COUNT = 5
+
+# This mimics the handle given by libusb1 for easy interoperability
+class SpiHandle:
+  def __init__(self):
+    self.spi = spidev.SpiDev()
+    self.spi.open(0, 0)
+
+    self.spi.max_speed_hz = 30000000
+
+  # helpers
+  def _transfer(self, endpoint, data, max_rx_len=1000):
+    for _ in range(MAX_RETRY_COUNT):
+      try:
+        packet = struct.pack("<BBHH", SYNC, endpoint, len(data), max_rx_len)
+        packet += bytes([reduce(lambda x, y: x^y, packet) ^ CHECKSUM_START])
+        self.spi.xfer2(packet)
+
+        dat = b"\x00"
+        while dat[0] not in [HACK, NACK]:
+          dat = self.spi.xfer2(b"\x12")
+
+        if dat[0] == NACK:
+          raise Exception("Got NACK response for header")
+
+        packet = bytes(data)
+        packet += bytes([reduce(lambda x, y: x^y, packet) ^ CHECKSUM_START])
+        self.spi.xfer2(packet)
+
+        dat = b"\x00"
+        while dat[0] not in [DACK, NACK]:
+          dat = self.spi.xfer2(b"\xab")
+
+        if dat[0] == NACK:
+          raise Exception("Got NACK response for data")
+
+        response_len = struct.unpack("<H", bytes(self.spi.xfer2(b"\x00" * 2)))[0]
+
+        dat = bytes(self.spi.xfer2(b"\x00" * (response_len + 1)))
+        # TODO: verify CRC
+        dat = dat[:-1]
+
+        return dat
+      except Exception:
+        pass
+    raise Exception(f"SPI transaction failed {MAX_RETRY_COUNT} times")
+
+  # libusb1 functions
+  def close(self):
+    self.spi.close()
+
+  def controlWrite(self, request_type, request, value, index, data, timeout=0):
+    return self._transfer(0, struct.pack("<HHHH", request, value, index, 0))
+
+  def controlRead(self, request_type, request, value, index, length, timeout=0):
+    return self._transfer(0, struct.pack("<HHHH", request, value, index, length))
+
+  # TODO: implement these
+  def bulkWrite(self, endpoint, data, timeout=0):
+    pass
+
+  def bulkRead(self, endpoint, data, timeout=0):
+    pass