MEMS3 Extended Firmware Memory Map – Enables Map Switching on Freelander

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Using my MEMS3 Mapper you can now rearrange the memory map of a MEMS3, gaining 8kB of firmware space for patched and alternate maps.

I was recently asked to looked at extending my dual-map live-switching system to cover Land Rover Freelander ECUs. These were unable to implement the original solution due to lack of free firmware EEPROM space.

In order to make this viable, I’ve come up with a way of reorganising the address space of the ECU’s EEPROM. The EEPROM is divided into sectors as shown in the diagrams below. You can read any address at random. You can only write by converting logical 1s to 0s, you cannot write a 1 the top of a 0. In order to write new data, you have to erase a location first. But the chip only allows whole sectors to be erased, not individual addresses. For this reason, it is important that the address boundaries of the different areas used by the ECU align with the sector boundaries used by the chip, so that we can for example erase the map without erasing part of the firmware.

Later EU4 (Chinese/Continental MG TF LE500) ECUs used a different EEPROM chip (29F400 instead of 29F200) with twice the capacity and a different sector map. This required a rearrangement of the address map used by the ECU. One of the changes they made was to move the VIN and ZCS coding areas into the same sector as the boot loader. This made them effectively inaccessible to direct reads (the ECU firmware prohibits direct reading of the boot sector) and impossible to erase using existing ECU functions (as all programming operations are managed by the boot loader which is in the same sector, so erasing the coding would also erase the running boot loader and permanently “brick” the ECU).

It occurred to me that if I could find a way of moving the VIN and ZCS coding into the boot sector on an EU3 ECU, I could the re-designate the coding sector as an additional firmware sector (it follows on directly after the last firmware sector in the EEPROM), giving an additional 8kB of firmware space. This would be about twice what was needed in order to enable map switching on a Freelander.

Doing this would require a new, modified boot loader writing for the ECU. Nearly all of the MEMS£ boot loaders across all of the range of part numbers are identical, other than for a few bytes which code the part number and the boot loader ID. The only exceptions are some very early ECUs where the boot loader appears to have been still under development (and full of bugs!) and the very latest VVC 160 ECUs, where a new boot loader bootp039 was used. This means that I could develop a single replacement 

The Extended Firmware Memory Map

There are now two different memory maps for EU3 petrol MEMS3s supported by MEMS3 Mapper.

Shown on the left is the Standard Memory Map. Shown on the right is the new Extended Firmware Memory Map. In this memory map the VIN and ZCS coding are moved into unused space in the boot loader sector of the EEPROM from $100000-$10FFFF (as was done in the later EU4 Chinese Continental MG TF LE500 version of the ECU). The VIN coding starts at $10C000 and the ZCS coding starts at $10D000. The EEPROM sector from $13A000-$13BFFF which was allocated to VIN and ZCS coding now becomes another sector allocated to Firmware, extending the available firmware space from 168kB to 176kB.

Modified Boot Loader

Each of these memory maps is supported by different (sets of) boot loaders. The standard memory map uses a range of boot loaders with IDs beginning “bootp”, e.g. “bootp004” … “bootp039” (a different boot ID is generally associated with each part number, some part numbers e.g. NNN000160 came with more than one boot loader e.g. “bootp033” and “bootp039”). The extended firmware memory map has one single boot loader “bootx033” which should be useable with any petrol MEMS3 hardware and firmware combination and may therefore be associated with multiple part numbers.

Each of the memory maps has its own version of MEMS3 Mapper, which is built with a memory map to match that of the ECU. The standard memory map is served by “MEMS3 Mapper EU3” with executable files “Mems3Mapper.32.exe” (32-bit) and “Mems3Mapper.64.exe” (64-bit). The extended firmware memory map is served by “MEMS3 Mapper XFW” with executable files “Mems3Mapper.ExtendedFirmware.32.exe” (32-bit) and “Mems3Mapper.ExtendedFirmware.64.exe” (64-bit). Version 7.35 Release or later is required to support these features.

Each of these versions of MEMS3 Mapper will only allow you connect and talk to ECUs with the appropriate memory map. To help enforce this, when the boot loader is flashed the part number is automatically updated. The standard memory map boot loaders set part numbers beginning with “NNN”, the extended firmware memory map boot loader sets part numbers beginning with “NNX” (the remaining 6 numeric digits remain unchanged).

In order to facilitate the flashing of the appropriate boot loaders, during which the ECU may change from one memory map to the other, each MEMS3 Mapper version allows you to connect to ECUs with the other memory map when clicking “About ECU” and in the limited circumstances used to check that a boot loader flash has succeeded. Under all other circumstances, connecting to an ECU with the wrong build of MEMS3 Mapper will display an error message similar to the one below:



Other than for some very small changes to the way the VIN and ZCS coding is handled (the full previous coding history is not displayed in the dialogs), the two versions of MEMS3 Mapper are identical in use and the ECU will operate in exactly the same way with either memory map.

Firmware Changes

As well as changes to the boot loader, the different memory maps require changes to the firmware. These are to support the firmware functions for reading and writing VIN and ZCS coding records and to correct the runtime checksum verification routines. MEMS3 Mapper EU3 with the standard memory map saves projects in files with a “.MM3” extension. MEMS3 Mapper XFW with the extended firmware memory map saves projects in files with a “.MX3” extension, but has been built to allow it to open “.MM3” files from the standard memory map version, as well as plain binaries from standard memory map ECUs. On opening a project or binary, it automatically scans the firmware code to determine which memory map it supports and if it finds a standard memory map firmware it patches it on the fly to extended firmware memory map. This means that all existing MEMS3 Mapper EU3 projects and reads from a standard memory map ECU can be opened in MEMS3 Mapper XFW and flashed to an extended firmware memory map ECU without any explicit changes being required.


The process of converting a standard memory map ECU to use the extended firmware memory map is therefore:

·         Start off using MEMS3 Mapper EU3 with the standard memory map. This is required to connect to the ECU while it is still has the standard memory map.

·         If you want to continue to use the firmware and map currently installed, then read and save it now as the process of flashing the boot loader will erase it.

·         Flash the extended memory map boot loader onto the ECU. There are two alternative ways of doing this:

o   By writing a boot loader file directly. Select Tools | ECU Tools | Write Boot Loader File from the menu. Confirm with Yes. When prompted with a dialog, select the file “Rover K-Series - Extended Firmware -” in the “Boot Loaders\Rover K-Series\” subfolder within the MEMS3 Mapper installation folder. This will erase the firmware and map, upload the new boot loader into the firmware area, verify it (for robustness the write and verify are always done at 1x Speed so take approximately 4 minutes to complete), then ask you if you want to proceed with the update. Click Yes. A custom program is uploaded into RAM to perform the boot loader update. DO NOT INTERRUPT THE PROCESS OR POWER THE ECU OFF DURING THE UPDATE which usually only takes 2-3 seconds.

o   By using a boot loader update package. Open the file “Boot Update - Rover K-Series - Extended Firmware - bootx033.mm3” in the “Boot Updates\Rover K-Series\” subfolder within the MEMS3 Mapper installation folder. Click Write. Confirm with Yes. The entire boot loader update process should now complete automatically.

o   Whichever method you choose, you should see a dialog like this, confirming the new boot loader and part number:


·         The ECU now has the extended firmware memory map. So to continue to work with it, you need to switch to MEMS3 Mapper XFW with the extended firmware memory map.

·         Open the firmware and map project you want to flash back onto the ECU. This may or may not be the one you read off at the start of the process. Opening the file in MEMS3 Mapper XFW will automatically upgrade the firmware in the project to use the extended firmware memory map.

·         If you want to install a map switching patch, install it into the project now.

·         Write the project to the ECU in the normal way. You should see a dialog similar to this:

The example shown started as a Freelander ECU NNN100710 which would not have supported dual map switching with the standard memory map, but which is now able to support dual maps when converted to the extended firmware memory map as an NNX100710.

·         You can then apply any VIN and ZCS coding. These continue to operate in the normal way, despite the new storage locations:

If you ever want to convert an ECU back to the standard memory map, use exactly the same process but start off using MEMS3 Mapper XFW with the extended firmware memory map, write a standard memory map boot loader, then switch to MEMS3 Mapper EU3 with the standard boot loader to continue.