Programming the Onboard I2C EEPROM


Downloading the firmware to the internal RAM of the EZ-USB device is a nice thing during development. It gives you increased flexibility and shorter turnaround cycles when building or debugging the code. Furthermore a board is not destined to a single purpose but can serve different applications by exchanging the firmware online. This can even be automated when the systems sees the need for a certain functionality.
All this works fine with a properly configured host in the background and if the user has the ability to guide its mechanisms. Still there are scenarios where all this is just bothering. Either because a device is selected to run the same firmware all the time or because there are no means to transfer the firmware into internal RAM. Expecially when a device should be connected to different hosts running different operationg systems or there is no chance to download directly after the host's system start.
Here, the need arises to place the firmware permanently into a non-volatile memory getting benefit from the feature that the EZ-USB is able to load its RAM from an onboard EEPROM.

Data preparation

The compiled firmware has to be reordered to fit the format which is expected by the boot-loader. No matter how you program the EEPROM, a conversion has to take place that results in a structure as specified in the by Cypress (for details refer to "The EZ-USB Integrated Circuit Technical Reference Manual" v1.9, section 5.8).
This task is performed by the script It takes the compiled firmware in IHEX-format and outputs a reformatted version of it.
Run it as < firmware.ihx > e2_data.ihx

EEPROM programming

After the preparation step all input data for the programming process is available. In case you own an E(E)PROM programmer, put in the EEPROM and load the reformatted ihex-file. This can be annoying and is in fact not necessary. Just use the EZ-USB to program its onboard EEPROM itself.
The firmware i2c_firm in the tools directory turns the EZ-USB device into an I2C-programmer which receives data via USB and places it into the EEPROM. It can read out the EEPROM for test purposes as well and returns the content back to the host computer. Just build the firmware and transfer it to the EZ-USB in the usual way. On the host side there is a perl script called that reads in an ihex-file and sends the data to the board.
For example -d /proc/bus/usb/001/011 -w -i e2_data.ihx
will send the content of e2_data.ihx to the specified USB device.
Single bytes can be written as well: -d /proc/bus/usb/001/011 -w -a 0x0200 -l 2 -D "0xaf 0xfe"
This will place the two bytes 0xaf and 0xfe at address 0x0200 and 0x0201 in the EEPROM.
To verify that the bytes have been actually written, execute the following: -d /proc/bus/usb/001/011 -r -a 0x0200 -l 2
For all options run -h or have a look at the script code. You will need libusb and the USB perl module to access USB devices from userland.


There might be times during debugging when you are confronted with the problem that your buggy little firmware hangs the EZ-USB so bad that it is no longer possible to download anything to internal RAM. Unplugging the board won't help If the firmware resides in the EEPROM. Your only chance to overwrite the troublesome memory content is to disable the EEPROM before the EZ-USB is powered on to prevent the USB core from boot-loading the firmware. Enable the EEPROM again, download i2_firm and finally clean at least the first byte. Here you must tweak and disable I2C autodetection. Specify the correct bus address and address size. This is necessary because the USB core will store the information that there is no EEPROM present at power-up and autodetection in i2_firm will guess the wrong type.
Fell free to contact me if you have problems with this.

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