If you use Homebrew, follow the "Alternate Flashing Method" (near the bottom) instructions at http://www.intel.com/content/www/us/en/support/boards-and-kits/000005801.html

Here is a modified version if you are using Mac Ports. IMPORTANT: DO NOT UNPLUG DURING THE FLASHING PROCESS!

1. Instal utilities

 sudo port install dfu-util coreutils getopt

2. Get the latest "Yocto complete image" from https://software.intel.com/en-us/iot/hardware/edison/downloads, e.g., edison-iotdk-image-280915.zip

3. mkdir edison-iotdk-image-280915.zip && cd edison-iotdk-image-280915.zip

4. Untar the image, e.g.,

 unzip ../edison-iotdk-image-280915.zip

5. Edit flashall.sh, and comment out the following l ine:

 if "$OSTYPE" == "darwin"* ? ; then READLINK=greadlink; GETOPTS="$(brew list gnu-getopt | grep bin/getopt)"; else READLINK=readlink;fi;

then add right before or after it this line:

 READLINK=/opt/local/bin/greadlink

Save and quit the editor

6. Unplug the board then run

 ./flashall.sh

7. Plug the board and wait. The script can take up to 5 minutes to complete the flashing. Wait at least 2 minutes after it's done to unplug the board.

Sample output:

 ./flashall.sh
Using U-Boot target: edison-blankcdc
Now waiting for dfu device 8087:0a99
Please plug and reboot the board
dfu-util: Device has DFU interface, but has no DFU functional descriptor
Flashing IFWI
Flashing U-Boot
Flashing U-Boot Environment
Flashing U-Boot Environment Backup
Rebooting to apply partition changes
Now waiting for dfu device 8087:0a99
Timed out while waiting for dfu device 8087:0a99
DEBUG: lsusb
Bus 021 Device 028: ID 05ac:8406 Apple Inc. Internal Memory Card Reader  Serial: 000000000820
Bus 020 Device 032: ID 8087:0a9e Intel Corporation Edison  Serial: 736635fa9ad782b02c3ace21e3e8916d
Bus 020 Device 010: ID 0403:6001 Future Technology Devices International Limited FT232R USB UART  Serial: A903JO8L
Bus 020 Device 006: ID 0a5c:4500 Broadcom Corp. BRCM20702 Hub 
Bus 020 Device 013: ID 05ac:8289 Apple Inc. Bluetooth USB Host Controller 
Bus 020 Device 005: ID 05ac:0262 Apple Inc. Apple Internal Keyboard / Trackpad 
Bus 010 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub 
Bus 010 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub 
DEBUG: dfu-util -l
dfu-util 0.8

Copyright 2005-2009 Weston Schmidt, Harald Welte and OpenMoko Inc.
Copyright 2010-2014 Tormod Volden and Stefan Schmidt
This program is Free Software and has ABSOLUTELY NO WARRANTY
Please report bugs to dfu-util@lists.gnumonks.org

8. You should be able to see a device name starting with /dev/cu.usbserial-, then try connecting:

  screen -L  /dev/cu.usbserial-A903JO8L 115200 -L

replacing A903JO8L with the string for your device. Make sure to press Enter twice after the above command.