3 ms·
That actually surprises me.. I would have guessed that there would be some amount of metadata you could query over the data lines, such as the specs for the DIM
by bodyfour 12y ago
That actually surprises me.. I would have guessed that there would be some amount of metadata you could query over the data lines, such as the specs for the DIMM. I guess that's all sent over I2C or something instead?
- makomk 12y agoYeah, that's all done through a seperate EEPROM chip accessed over SMBUS, which is essentially the same as I2C. Raw SDRAM chips don't provide any way to query their specification; on embedded systems that use them, the settings are generally all hardcoded in the bootloader.
- tcas 12y agoSDRAM's interface doesn't leave room for extra commands, it's pretty much designed to read/store data and refresh content. It only has 3 lines to select the command (RAS#, CAS#, WE#). Other RAMs/Flash with different interfaces (e.g. SPI) require a prefix command to be sent over the wire, so it's easier for them to implement things like chip id commands.
- kenz0r 12y agoI don't think that is exactly true. DRAM from SDRAM up has had a number of mode registers to control the ram. More info here: http://en.wikipedia.org/wiki/Synchronous_dynamic_random-access_memory#SDRAM_mode_register http://en.wikipedia.org/wiki/Synchronous_dynamic_random-acce...
- cnvogel 12y agoExactly. ...here's the table for command accesses on DDR4, including the mode register you referred to. http://en.wikipedia.org/wiki/DDR4_SDRAM#Command_encoding http://en.wikipedia.org/wiki/DDR4_SDRAM#Command_encoding