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pcercuei / UBIBoot

Small bootloader for Ingenic JZ47xx based boards
GNU General Public License v2.0
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Enhancement: increase SDRAM speed on JZ4725B based handhelds. #4

Closed SiarheiVolkau closed 3 years ago

SiarheiVolkau commented 3 years ago

The SDRAM clock ratio seems not optimal for JZ4725B based devices (RS-90, RG99). Current ratio is /4 which leads to 90MHz effective clock speed on default 360MHz CPU clock.
It's possible to set ratio to /3 thus get 120MHz effective SDRAM frequency which lead to better overall performance. Has tested on similar device Ritmix RZX-27 (JZ4725B and Etrontech EM63A165TS-6G SDRAM chip) and observed performance is 10-20% better on the same CPU speed.
Unfortunately the maximal CPU overclock is limited by 420MHz but performance seems higher than on 456MHz CPU clock with /4 ratio of SDRAM. How to set ratio /3 - redefine HDIV and PDIV and MDIV to 2 in the desired board file.

pcercuei commented 3 years ago

Sorry, I didn't see this bug report.

I don't know what you are talking about though. Current ratios are already /3. If you set HDIV/PDIV/MDIV to 2, then the ratios are /2.

SiarheiVolkau commented 3 years ago

Yep, you are right, I miss the n2FR array usage, sorry. BTW my handheld is able to work on the /2 rates, but it is out of specifications and not very stable. So no actions needed, thank you.

pcercuei commented 3 years ago

@SiarheiVolkau One thing you can try is to set the PLL to 2x its nominal frequency (e.g. 360 MHz -> 720 MHz) and use dividers 2/6/6/6/6. Strangely on lepus boards (JZ4760) that makes a noticeable difference. I didn't test on the JZ4725B.