16MB PSRAM Chips For Teensy 4.1 Now Available
Teensy 4.1 has locations for 2 memory chips to be installed on the bottom side. Up until now, we have been limited to 8MB PSRAM chips for adding volatile memory to the Teensy 4.1 which allowed for 8MB PSRAM and a Flash chip or 16MB PSRAM.
destradigelagarina.it, PJRC and the Teensy community have worked together to make a new 16MB PSRAM chip and software support available for the Teensy 4.1. It is the ISSI PN: IS66WVS16M8FBLL. These parts are not currently available from general distributors.
This part allows for up to 32MB of PSRAM memory or 16MB PSRAM plus a Flash chip. We offer Teensy 4.1 with these parts preinstalled and tested in our various custom configurations as well as make the bare chips available in small quantities for DIY’ers.
PSRAM is dynamic memory accessed over a dedicated high speed QSPI bus. It is slower than the built-in 1MB RAM of the Teensy NXP processor, but can be quite useful as scratchpad memory for adding audio delays or manipulating large arrays or structures and things of that nature that won’t fit into the processor memory.
More information on Teensy memory can be found at the following link:
The use of these chips require an update in Teensyduino to version 1.60 Beta #5 or later. The beta #5 can be found at the following link:
https://forum.pjrc.com/index.php?threads/teensyduino-1-60-beta-5.77176
This Teensyduino release also increases the default QSPI bus speed from 88MHz to 105.6MHz. We test the parts we preinstall at a 120MHz bus speed which is the fastest speed that these 16MB chips operate reliably at.
Deciding between 8MB vs 16MB PSRAM Chips
The obvious difference is that the 16MB PSRAM chips have twice the memory capacity, but they also cost more than the 8MB parts for the same amount of memory.
Another factor is if you are wanting to push the performance of the PSRAM by increasing the QSPI bus speed from the default 105.6MHz. The 8MB parts can be pushed harder and will run at up to 166MHz in our testing when using the AP 6404L-3SQR part which we currently use. The 16MB parts on the other hand can only handle about 120MHz when 2 of the chips are installed. The 16MB parts use two 8MB dies internally, so they undoubtedly load the QSPI bus more than the 8MB parts which may account for the speed difference.
If a Flash chip is installed instead of a 2nd PSRAM, that will limit the 8MB PSRAM parts to 132MHz due to the slower Flash installed on the same bus. The 16MB will still operate at 120MHz when coupled with a Flash chip.
If you don’t need more than 16MB PSRAM and no Flash, we recommend using 2 of the 8MB parts. They are less expensive and can potentially operate faster, but if bigger is better for your project then the 16MB parts are a nice option to have.
Here are a few links to products with these parts:
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