Advantages of SPMI interface | Disadvantages of SPMI protocol

This page covers advantages and disadvantages of SPMI interface protocol. It mentions benefits or advantages of SPMI interface and drawbacks or disadvantages of SPMI protocol.

Introduction : It has been developed to address complexity and performance requirements of smartphones, mobile phones, wearables and other portable electronic devices. It simplifies power management and data transfer between ICs in order to reduce power consumption and enhance battery life. It reduces pin count in hardware architecture of portable devices to greater extent.

What is SPMI protocol ?

SPMI is the short form of System Power Management Interface. The specifications of SPMI are defined and managed by MIPI Alliance. It is 2 wire bi-directional interface with lines SDATA and SCLK. It supports multi-master and multi-slave configurations. In this protocol, Slaves work in two modes viz. request capable and non-request capable. It monitors performance of the processor in given load condition and application of usage. It also controls various supply voltages as per performance level requirements.

SPMI interface diagram
Image Courtesy : MIPI Alliance

SPMI protocol interfaces power controller of SoC with one or more PMICs (Power Management ICs). This protocol adjusts supply and substrate bias voltages dynamically inside SoC using single SPMI bus. Within power controller of SoC, SPMI functions are known as "master" where as within PMIC, SPMI functions are known as "Slave". SPMI supports maximum of 4 masters and 16 slaves. Multiple masters and slaves are available on single IC or several ICs or combination of both. Following table mentions features of SPMI protocol.

SPMI Features Description
Signals SDATA : Bi-directional serial data signal
SCLK : Uni-directional clock signal
Bus arbitration Uses round robin priority algorithm for equal bus access by masters, A-bit/SR-bit arbitration for slaves etc.
Device classes High speed (32 KHz to 26 MHz), Low speed (32 KHz to 15 MHz)
Frame types Command Frame , Data and address frame and No response frame
ACK/NACK Requires for robust communication.
Error detection Uses odd parity bit
Burst read/write Upto 16 bytes with 8 bit addressing, Upto 8 bytes with 16 bit addressing
Slave Group IDs It is used for simultaneous write commands to multiple slaves.
Signaling voltages 1.2V , 1.8V
Loading Up to 50pF is used on SDATA and SCLK
Command types supported Power management commands such as Reset, Shutdown, Sleep, Wakeup and authenticate. It supports read/write commands in various configurations such as master-master, master-slave, slave-master and slave-slave.

Benefits or advantages of SPMI

Following are the benefits or advantages of SPMI:
➨It replaces point to point topology with bus architecture. Hence it reduces pin counts of SoCs.
➨Multi master/slave feature allows chipset partitioning based on hardware complexity and load distribution.
➨Use of ACK/NACK allows confirmity to correct completion of commands.
➨It offers high speed.
➨It offers low latency.
➨It offers real time control of voltage as well as frequency.

Drawbacks or disadvantages of SPMI

Following are the drawbacks or disadvantages of SPMI:
➨SPMI v2.0 devices are not compatible with SPMI v1.0 devices.
➨Like other serial communication interfaces, it is also affected by noise, reset issues, board layout and minor differences in its implementations. This sometimes results into bus errors and system malfunctioning.

Refer advantages and disadvantages of following interface protocols.
UART,   SPI,   I2C,   I2S,   Serial interface,   Parallel interface

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