I can not find any 8 gigabit memory for the STM32MP157CAA3 What I have found is double the price of the processor! IS46TR16512BL ISSI and Micron ECF840AAACN-C1-Y3

[KevinA]

I can not find any 8 gigabit memory for the STM32MP157CAA3 What I have found is double the price of the processor! IS46TR16512BL ISSI and Micron ECF840AAACN-C1-Y3

I was looking for 256X32 memory but gave up, found some 512X16 but this puts the the cost three times the napkin estimate, instead of $10 for memory it is $30, and that's if it is available !

[PatrickF]

I agree that DDR are quite pricey this time, especially when going for small quantities thru distributors.

Note that IS46TR16512BL is Automotive grade, so higher price if not what you ask for.

8Gbit DDR3L x16 is not frequent, and we recommend to use 2x4Gbit devices in x32 (as on our STM32MP157C-EV1 board).

LPDDR has a price premium due to it's low power Vs DDR3L.

You also need to check if your application absolutely need 8Gbit, many embedded Linux products could run very well with a single 4Gbit x16

You could probably found MT41K256M16 at about 5$ (the one we have on our STM32MP157C-DK2 board).

Regards,

[KevinA]

I just found MT41K512M16HA-107 at Microns web site, Mouser stocks it and sells it in QTY 1, pricey but do-able... The question is why no DDR3 that is 32 bit wide?

[PatrickF]

DDR3L come initially from PC market and standardized by JEDEC. My understanding is that in order to reach high frequencies and high density on SODIMM, it is always easier to have multiple x8 or x16 devices to form a x32 or x64 bus, which keep the data lanes in point2point connection, instead of managing multiple rank (ChipSelects) which end up to very complex signal integrity for data lanes. Single die highest density is usually linked to technology node.

LPDDR2 or LPDDR3 come from mobile phone market, where size and power matters, so mostly x32 are available (usually is much finer ball pitch than DDR3L).

[KevinA]

I was looking at the D2 schematic and it dawned on me to just add another 256X16 and hook the DQ16~DQ32 lines up. I can get the 256X16 for $3 each! Anyone see any reason this wouldn't work?

I'd have to tell the memory controller about the buss width is the only thing I see... but there something else, A15 is still not used, can I have two 512X16 which would require the A15 line and give me 2GB ?

[KevinA]

Our application is CNN with video and multiple cameras, yes I signed up for the AI Webinar.

[PatrickF]

No issue to extend schematics to 2 x 4Gbit (this would then be similar to STM32MP157C-EV1 schematics, except the use of smaller TFBGA361 package instead of LFBGA448). In DDR3L x32, the use of VTT and termination resistor is mandatory as address/command bus will be routed to 2 packages (termination are optional when used in x16 with a single device).

Then with an updated Device Tree to your new HW (using CubeMx and DDR Tools to tune up the DDR settings to your PCB), it will work without much issues.

HW and memory mapping is limited to 1GByte, not possible to go beyond. A15 is only used with 512Mx16 device, but only one device is supported due to the 1Gbyte limit.

[Alex - APMemory]

fyi, if you look for 8Gb DDR3L x16 support at competitive price I'll suggest Zentel Japan A3T8GF43BBF-GML (https://www.zentel-japan.com/BeDownloadFiles/DSA3T8GF343BBFLF.06.pdf)

You can look at below link and sort by price, just as general reference & comparison purpose

https://eu.mouser.com/c/semiconductors/memory-ics/dram/?memory%20size=8%20Gbit&organization=512%20M%20x%2016&type=SDRAM%20-%20DDR3L&sort=pricing

Using 2 pces of 4Gb DDR3 remains obviously another solution

Alex