I2C Busy Timeout

I'm debugging both python host code (ethernet) and microcontroller firmware (I2C), with a labjack T7 in between.

I'm using I2C clock stretching to hold the I2C bus while the uC is preparing a response from incoming T7 commands. The T7 is the master, the uC is the slave. The uC invokes clock-stretching by holding SCL low.

Sometimes, if my poorly-written uC firmware takes too long, and LJM returns with an "I2C_BUS_BUSY" error.

For example:

 Bytes_To_Read = write_device(daq, sout, verbose=verbose) #updates Bytes_To_Read with length-to-read
  File ".\sc_NERDAQ_I2C.py", line 261, in write_device
    ljm.eWriteName(daq, "I2C_GO", 1)
  File "C:\Python27\lib\site-packages\labjack\ljm\ljm.py", line 530, in eWriteName
    raise LJMError(error)
labjack.ljm.ljm.LJMError: LJM library error code 2720 I2C_BUS_BUSY

This particular instance happened when my uC was holding SCL low for ~280 mSec (delaying the ACK of the address byte).  Yes, I know that this is slow, and something is broken. 

However, I'm wondering:

• What determines this I2C "GO" Timeout?
• Is the timeout value readable/setable?
• Am I correct that Ethernet Transaction Timeout is a default of 2600 mS (or thereabouts), so it's probably not that?

I2C Setup:

# Configure the T7 for I2C-serial
my_list = [
    "I2C_SDA_DIONUM",
    "I2C_SCL_DIONUM",
    "I2C_SPEED_THROTTLE",
    "I2C_OPTIONS",
    "I2C_SLAVE_ADDRESS",
]
my_data = [
    int(SDA_pin),
    int(SCL_pin),
    65516,  # Speed Throttle 65,516 is ~100 kHz, min is 46,000 (per LJM library)
    0b00000000,  #I2C options B2: disable clock stretching, B1: No STOP with RESTART, B0: Reset Bus
    int(MIN_I2C_ADDRESS),  # junk, default I2C_address of a widget
]
ljm.eWriteNames(daq, len(my_list), my_list, my_data)

Trace results of writing to I2C widget at address 0x14 "X\0x10", followed by a Read request to the same address, with clock stretching (delaying the ACK of the Address-Read byte) starting at ~390 uS:

See Attachment.

Sending code:

ljm.eWriteName(daq, "I2C_NUM_BYTES_TX", len(bytes_in))  # number of bytes in the original data
ljm.eWriteName(daq, "I2C_NUM_BYTES_RX", 1)              # read-back the length of any response, 0-128
ljm.eWriteNameByteArray(daq, "I2C_DATA_TX", len(bytes_in), [ord(ch) for ch in bytes_in])        #convert string to list of ints
ljm.eWriteName(daq, "I2C_GO", 1)

< I2C Busy Error Here >

#Get the LabJack buffer contents, that was updated from "I2C_GO".
resp = read_LabJack_I2C_buffer(daq, 1, verbose=verbose)  

Thank you for your attention.

-Chris