Easyi3C is a leading supplier of embedded system tools that simplify the development and debugging of various communication protocols. The company offers a range of products designed to help engineers and developers use I3C/I2C , USB and MIPI, JEDEC, MCTP and other protocols more efficiently.

Testing DDR5 RCD based on Tower I3C Host Adapter (4)

1. Background introduction to DDR5 RCD I3C

In the field of high-performance computing and servers, DDR5 RCD and I3C bus are core technologies that ensure data centers can support massive memory capacity and extremely high transmission rates.

Simply put, if we compare server memory (RDIMM) to a busy high-speed rail station, RCD is the "central control room" that commands and dispatches, while I3C is the "ultra-high-speed internal telephone" that connects various monitoring and management units.

1) DDR5 RCD (Register Clock Driver)

In servers, to increase memory capacity, a large number of memory chips (DRAM) are typically mounted on a single channel. However, this presents a physical challenge: excessive signal load, leading to electrical signal attenuation and timing irregularities.

core role

• Signal retiming and buffering : The RCD is located at the center of the memory module (RDIMM). Its task is to receive instruction and address signals from the CPU memory controller, "shape" and "amplify" them, and then distribute them to the individual DRAM chips on the memory module.

• Reduced charge load : For the CPU, it only needs to deal with one RCD instead of dozens of DRAM chips, which greatly improves the signal integrity of the system.

• The evolution of DDR5 : Compared to DDR4, DDR5 RCD introduces more complex decision logic, supports higher frequencies (starting from 4800MT/s and moving towards 8400MT/s+), and improves bandwidth efficiency with dual-channel architecture.

2) I3C Protocol Background

In the DDR4 era, auxiliary management of memory modules (such as reading temperature sensors and SPD configuration information) mainly relied on the outdated I2C or SMBus . However, with technological advancements, I2C has become a bottleneck.

• Too slow : the highest speed is only around 1MHz.

• High power consumption : Open-drain circuit with pull-up resistors.

• Lack of in-band interrupts : Unable to proactively and quickly report urgent errors to the CPU.

Why did DDR5 introduce I3C?

MIPI I3C (Improved Inter-Integrated Circuit) is a next-generation bus protocol that is backward compatible with I2C and has been selected by the JEDEC organization as the sideband management standard for DDR5.

• Lightning-fast response : The speed has been increased to 12.5MHz, which increases the speed of reading SPD (configuration information) or temperature control data by more than ten times.
  

• In-band interrupt (IBI) : When the memory module overheats or the voltage is abnormal, the RCD or integrated sensor can "actively interrupt" the system to report the fault via the I3C bus without the CPU constantly polling.

• More energy efficient : The push-pull output significantly reduces power consumption during high-frequency communication.

3) Collaboration between RCD and I3C

On DDR5 memory modules, the RCD is not only responsible for data signals, but it also integrates an I3C Hub (or acts as a slave device) .

4) Write Protocol

DDR5 RCD I3C write operations typically use Write DWord, Write Byte, Write Word . The I3C protocol supports a relatively complex set of formats; according to the JEDEC specification, it needs to support the following formats:

5) Read Protocol

DDR5 RCD I3C read operations typically use Block Mode, which includes PEC Disabled or PEC Enabled.

According to the JEDEC Specification, the following format needs to be supported:

Next, we will explain in detail how to use the Tower I3C Host Adapter to test the I3C of the RCD.