i.MX27 and i.MX31 Issues When Interfacing Micron's 78nm mDDRs
Micron is discontinuing some "-75" mDDR parts (133MHz) popular on i.MX27 and i.MX31 designs, newer "-6" are being used to replace the EOL devices. However, loss of data issues may be experienced when i.MX mDDR controller is used to interface with newer Micron's mDDR.
On some cases, the bootloader works, memory tests on RedBoot pass. However, Linux hangs when booting.
Here are the DDR Controller configuration changes that may be used to avoid the issue: (This configuration is not proven to work on every design, but has been validated on at least 3 different boards.)
ESDRAMC Configuration Registers
Set ESDCFG0/1 to 0x0079D72F
0xD800_1004 = 0x79D72F
Drive Strength Control Registers
Use "Normal". i.MX27 Default.
Enhanced MDDR Delay Line Configuration Debug Register