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fix read_fifo to always define packet before return, Correct typo in dosctring #6

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Merged
merged 3 commits into from
Dec 13, 2024
Merged

fix read_fifo to always define packet before return, Correct typo in dosctring #6

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bb4e3b5
fix read_fifo to always define packet before return, Corrct typo in r…
jerryneedell Dec 4, 2024
98c3141
fixup packet=None handling
jerryneedell Dec 6, 2024
87fe934
fix import in rfm9x
jerryneedell Dec 6, 2024
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1 change: 1 addition & 0 deletions adafruit_rfm/rfm69.py
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Original file line number Diff line number Diff line change
Expand Up @@ -643,6 +643,7 @@ def read_fifo(self) -> bytearray:
"""Read the packet from the FIFO."""
# Read the length of the FIFO.
fifo_length = self.read_u8(_RF69_REG_00_FIFO)
packet = None # return None if FIFO empty
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See my other comment re: returning None.

if fifo_length > 0: # read and clear the FIFO if anything in it
packet = bytearray(fifo_length)
# read the packet
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3 changes: 2 additions & 1 deletion adafruit_rfm/rfm9x.py
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Expand Up @@ -131,7 +131,7 @@ class RFM9x(RFMSPI):
- preamble_length: The length in bytes of the packet preamble (default 8).
- high_power: Boolean to indicate a high power board (RFM95, etc.). Default
is True for high power.
- baudrate: Baud rate of the SPI connection, default is 10mhz but you might
- baudrate: Baud rate of the SPI connection, default is 5mhz but you might
choose to lower to 1mhz if using long wires or a breadboard.
- agc: Boolean to Enable/Disable Automatic Gain Control - Default=False (AGC off)
- crc: Boolean to Enable/Disable Cyclic Redundancy Check - Default=True (CRC Enabled)
Expand Down Expand Up @@ -521,6 +521,7 @@ def read_fifo(self) -> bytearray:
"""Read the data from the FIFO."""
# Read the length of the FIFO.
fifo_length = self.read_u8(_RF95_REG_13_RX_NB_BYTES)
packet = None # return None if FIFO empty
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If this can return None, then the type annotation should specify Optional[bytearray]. Is it better to return an empty bytearray? Not entirely sure what the utility of each case is and which would be better.

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This might be important since the function that calls read_fifo checks len(packet). Please confirm. But this will probably not work on None. In that case bytearray(0) is probably the correct solution. I will change my test code to set packet = bytearray(0). Unless I report back assume it's working that way.

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And we're still left with the mystery about how read_fifo could be called with nothing in the FIFO - which was happening to me the other day. I can't tell if that's happening anymore with my rig. Nonetheless, I think this change and those in the other two files is best practice.

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If this can return None, then the type annotation should specify Optional[bytearray]. Is it better to return an empty bytearray? Not entirely sure what the utility of each case is and which would be better.

Good catch... I want to think about this a bit -- the calling code has a confusing check:

                    if len(packet) < 5:
                        # reject the packet if it is too small to contain the RadioHead Header
                        packet = None

which will clearly now fail if read_fifo returns None..... I think it best to use your original suggestion to make the return type annotation Optional[bytearray] and refactor the code to always check for packet is not None before checking len(packet). This way read_fifo will be consistent with receive in returning the Optional[bytearray]. Does that make sense?

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@jerryneedell jerryneedell Dec 6, 2024 •
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I changed it to Optional[bytearray] in the 3 files and in rfm_common.py changed code to avoid testing len(packet) if packet is None. Let me know what you think.

if fifo_length > 0: # read and clear the FIFO if anything in it
packet = bytearray(fifo_length)
current_addr = self.read_u8(_RF95_REG_10_FIFO_RX_CURRENT_ADDR)
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1 change: 1 addition & 0 deletions adafruit_rfm/rfm9xfsk.py
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Expand Up @@ -567,6 +567,7 @@ def read_fifo(self) -> bytearray:
"""Read the data from the FIFO."""
# Read the length of the FIFO.
fifo_length = self.read_u8(_RF95_REG_00_FIFO)
packet = None # return None if FIFO empty
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See my previous comment re: returning None.

if fifo_length > 0: # read and clear the FIFO if anything in it
packet = bytearray(fifo_length)
# read the packet
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