Fabric DDR Subsystem
Microsemi ProprietaryUG0446 User Guide Revision 7.0
145
4.6.1.1
DDRIO Calibration
Each DDRIO has an ODT feature, which is calibrated depending on the DDR I/O standard. DDR I/O
calibration occurs after the DDR I/Os are enabled. If the impedance feature is enabled, impedance can
be programmed to the desired value in three ways:
•
Calibrate the ODT/driver impedance with a calibration block (recommended)
•
Calibrate the ODT/driver impedance with fixed calibration codes
•
Configure the ODT/driver impedance to the desired value directly
The I/O calibration is always enabled when the DDR subsystem is configured for DDR2 and DDR3
memories.
The I/O calibration can be disabled or enabled using the DDR configurator when the DDR subsystem is
configured for LPDDR memories.
Note:
If I/O calibration is enabled, all I/Os in the DDR bank are calibrated even though the DDR controller is not
using all I/Os in the bank.
The FDDR_IO_CALIB_CR register can be configured for changing the ODT value to the desired value.
For more information on DDR I/O calibration, refer to the Configurable ODT and Driver Impedance
section of the I/Os chapter in the
UG0445: IGLOO2 FPGA and SmartFusion2 SoC FPGA Fabric User
.
Figure 76 •
Reset Sequence
4.6.2
ZQ Calibration
ZQ calibration is applicable for DDR3 only. This is used to calibrate DRAM output drivers (R
ON
) and on-
die termination (ODT) values. DDR3 SDRAM needs a longer time to calibrate R
ON
and ODT at
initialization and a relatively smaller time to perform periodic calibrations.
The DDR controller performs ZQ calibration by issuing a ZQ calibration long (ZQCL) command and ZQ
calibration short (ZQCS) command.
ZQCL is used to perform initial calibration during the power-up initialization sequence. This command is
allowed for a period of t
ZQinit
, as specified by memory vendor. The value of t
ZQinit
can be modified
through register bits REG_DDRC_T_ZQ_LONG_NOP,
The ZQCS command is used to perform periodic calibration to account for voltage and temperature
variations. A shorter timing window is provided to perform calibration and transfer of values as defined by
timing parameter tZQCS. The t
ZQCS
parameter can be modified through register bits
REG_DDRC_T_ZQ_SHORT_NOP,
PO_RESET_N
APB_S_PRESET_N
DDRIO
Calibration
MSS_RESET_N_M2F
or
HPMS_RESET_N_M2F
FPLL_LOCK
FDDR APB Register
Configuration
CORE_RESET_N