DRAM modules

When building one of the targets in rowhammer_tester/targets, a custom DRAM module can be specified using the --module argument. To find the default modules for each target, check the output of --help.

Note

Specifying different DRAM module makes most sense on boards that allow to easily replace the DRAM module, such as on ZCU104. On other boards it would be necessary to desolder the DRAM chip and solder a new one.

Adding new modules

LiteDRAM controller provides out-of-the-box support for many DRAM modules. Supported modules can be found in litedram/modules.py. If a module is not listed there, you can add a new definition.

To make developement more convenient, modules can be added in litex-rowhammer-tester repository directly in file rowhammer_tester/targets/modules.py. These definitions will be used before definitions in LiteDRAM.

Note

After ensuring that the module works correctly, a Pull Request to LiteDRAM should be created to add support for the module.

To add a new module definition, use the existing ones as a reference. New module class should derive from SDRAMModule (or the helper classes, e.g. DDR4Module). Timing/geometry values for a module have to be obtained from the revelant DRAM module’s datasheet. The timings in classes deriving from SDRAMModule are specified in nanoseconds. The timing value can also be specified as a 2-element tuple (ck, ns), in which case ck is the number of clock cycles and ns is the number of nanoseconds (and can be None). The highest of the resulting timing values will be used.

SPD EEPROM

On boards that use DIMM/SO-DIMM modules (e.g. ZCU104) it is possible to read the contents of the DRAM modules’s SPD EEPROM memory. SPD contains several essential module parameters that the memory controller needs in order to use the DRAM module. SPD EEPROM can be read over I2C bus.

Reading SPD EEPROM

To read the SPD memory use the script rowhammer_tester/scripts/spd_eeprom.py. First prepare the environment as described in Controlling the board. Then use the following command to read the contents of SPD EEPROM and save it to a file, for example:

python rowhammer_tester/scripts/spd_eeprom.py read MTA4ATF51264HZ-3G2J1.bin

The contents of the file can then be used to get DRAM module parameters. Use the following command to examine the parameters:

python rowhammer_tester/scripts/spd_eeprom.py show MTA4ATF51264HZ-3G2J1.bin 125e6

Note that system clock frequency must be passed as an argument to determine timing values in controller clock cycles.

Using SPD data

LiteDRAM does not yet allow to specify timing parameters at runtime. In order to use the new parameters it is necessary to rebuild the bitstream using the information extracted from the SPD memory. To do this use the --from-spd command line argument, for example:

make ARGS="--from-spd MTA4ATF51264HZ-3G2J1.bin" build

Then just load the new bitstream.

Note

Not supporting DRAM parameter configuration in runtime reduces resource usage of the LiteDRAM controller and is enough for most use cases. In the future runtime configuration is planned as optional feature.

Adding module configuration

After verifying that given module configuration stored in SPD works correctly it can be used to define module in Python. To do that use the output of spd_eeprom.py show to add a new module as described in Adding new modules