diff --git a/board/config.h b/board/config.h
index 6a25a398de..cc54df2569 100644
--- a/board/config.h
+++ b/board/config.h
@@ -6,6 +6,7 @@
 //#define DEBUG_USB
 //#define DEBUG_SPI
 //#define DEBUG_FAULTS
+//#define DEBUG_COMMS
 
 #define DEEPSLEEP_WAKEUP_DELAY 3U
 
diff --git a/board/main_comms.h b/board/main_comms.h
index 9f945cd6d9..cfc5388fb4 100644
--- a/board/main_comms.h
+++ b/board/main_comms.h
@@ -177,6 +177,14 @@ int comms_control_handler(ControlPacket_t *req, uint8_t *resp) {
   unsigned int resp_len = 0;
   uart_ring *ur = NULL;
   timestamp_t t;
+
+#ifdef DEBUG_COMMS
+  puts("raw control request: "); hexdump(req, sizeof(ControlPacket_t)); puts("\n");
+  puts("- request "); puth(req->request); puts("\n");
+  puts("- param1 "); puth(req->param1); puts("\n");
+  puts("- param2 "); puth(req->param2); puts("\n");
+#endif
+
   switch (req->request) {
     // **** 0xa0: get rtc time
     case 0xa0:
diff --git a/board/stm32fx/llspi.h b/board/stm32fx/llspi.h
index 83b65d9387..51bde6a2e4 100644
--- a/board/stm32fx/llspi.h
+++ b/board/stm32fx/llspi.h
@@ -61,7 +61,7 @@ void DMA2_Stream2_IRQ_Handler(void) {
     bool reponse_ack = false;
     if (check_checksum(spi_buf_rx + SPI_HEADER_SIZE, spi_data_len_mosi + 1)) {
       if (spi_endpoint == 0U) {
-        if (spi_data_len_mosi >= 8U) {
+        if (spi_data_len_mosi >= sizeof(ControlPacket_t)) {
           response_len = comms_control_handler((ControlPacket_t *)(spi_buf_rx + SPI_HEADER_SIZE), spi_buf_tx + 3);
           reponse_ack = true;
         } else {
diff --git a/python/__init__.py b/python/__init__.py
index 1bc51b68fd..1514340eb6 100644
--- a/python/__init__.py
+++ b/python/__init__.py
@@ -8,6 +8,7 @@
 import datetime
 import traceback
 import warnings
+import logging
 from functools import wraps
 from typing import Optional
 from itertools import accumulate
@@ -21,6 +22,11 @@
 
 __version__ = '0.0.10'
 
+# setup logging
+LOGLEVEL = os.environ.get('LOGLEVEL', 'INFO').upper()
+logging.basicConfig(level=LOGLEVEL, format='%(message)s')
+
+
 BASEDIR = os.path.join(os.path.dirname(os.path.realpath(__file__)), "../")
 
 DEBUG = os.getenv("PANDADEBUG") is not None
@@ -50,7 +56,7 @@ def pack_can_buffer(arr):
       snds.append(b'')
       idx += 1
 
-  #Apply counter to each 64 byte packet
+  # Apply counter to each 64 byte packet
   for idx in range(len(snds)):
     tx = b''
     counter = 0
diff --git a/python/spi.py b/python/spi.py
index a84c4c79d6..6a6569fed5 100644
--- a/python/spi.py
+++ b/python/spi.py
@@ -1,6 +1,9 @@
+import math
 import struct
 import spidev
+import logging
 from functools import reduce
+from typing import List
 
 # Constants
 SYNC = 0x5A
@@ -11,22 +14,37 @@
 
 MAX_RETRY_COUNT = 5
 
+USB_MAX_SIZE = 0x40
+
 # This mimics the handle given by libusb1 for easy interoperability
 class SpiHandle:
   def __init__(self):
-    self.spi = spidev.SpiDev()
+    self.spi = spidev.SpiDev()  # pylint: disable=c-extension-no-member
     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):
+  def _calc_checksum(self, data: List[int]) -> int:
+    cksum = CHECKSUM_START
+    for b in data:
+      cksum ^= b
+    return cksum
+
+  def _transfer(self, endpoint: int, data, max_rx_len: int = 1000) -> bytes:
+    logging.debug("starting transfer: endpoint=%d, max_rx_len=%d", endpoint, max_rx_len)
+    logging.debug("==============================================")
+
+    for n in range(MAX_RETRY_COUNT):
+      logging.debug("\ntry #%d", n+1)
       try:
+        logging.debug("- send header")
         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)
 
+        logging.debug("- waiting for ACK")
+        # TODO: add timeout?
         dat = b"\x00"
         while dat[0] not in [HACK, NACK]:
           dat = self.spi.xfer2(b"\x12")
@@ -34,10 +52,12 @@ def _transfer(self, endpoint, data, max_rx_len=1000):
         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])
+        # send data
+        logging.debug("- sending data")
+        packet = bytes([*data, self._calc_checksum(data)])
         self.spi.xfer2(packet)
 
+        logging.debug("- waiting for ACK")
         dat = b"\x00"
         while dat[0] not in [DACK, NACK]:
           dat = self.spi.xfer2(b"\xab")
@@ -45,30 +65,41 @@ def _transfer(self, endpoint, data, max_rx_len=1000):
         if dat[0] == NACK:
           raise Exception("Got NACK response for data")
 
-        response_len = struct.unpack("<H", bytes(self.spi.xfer2(b"\x00" * 2)))[0]
+        # get response length, then response
+        response_len_bytes = bytes(self.spi.xfer2(b"\x00" * 2))
+        response_len = struct.unpack("<H", response_len_bytes)[0]
 
+        logging.debug("- receiving response")
         dat = bytes(self.spi.xfer2(b"\x00" * (response_len + 1)))
-        # TODO: verify CRC
-        dat = dat[:-1]
+        if self._calc_checksum([DACK, *response_len_bytes, *dat]) != 0:
+          raise Exception("SPI got bad checksum")
 
-        return dat
+        return dat[:-1]
       except Exception:
-        pass
+        logging.exception("SPI transfer failed, %d retries left", n)
     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
+  def controlWrite(self, request_type: int, request: int, value: int, index: int, data, timeout: int = 0):
+    return self._transfer(0, struct.pack("<BHHH", request, value, index, 0))
+
+  def controlRead(self, request_type: int, request: int, value: int, index: int, length: int, timeout: int = 0):
+    return self._transfer(0, struct.pack("<BHHH", request, value, index, length))
+
+  # TODO: implement these properly
+  def bulkWrite(self, endpoint: int, data: List[int], timeout: int = 0) -> int:
+    for x in range(math.ceil(len(data) / USB_MAX_SIZE)):
+      self._transfer(endpoint, data[USB_MAX_SIZE*x:USB_MAX_SIZE*(x+1)])
+    return len(data)
+
+  def bulkRead(self, endpoint: int, length: int, timeout: int = 0) -> bytes:
+    ret: List[int] = []
+    for _ in range(math.ceil(length / USB_MAX_SIZE)):
+      d = self._transfer(endpoint, [], max_rx_len=USB_MAX_SIZE)
+      ret += d
+      if len(d) < USB_MAX_SIZE:
+        break
+    return bytes(ret)