I'm wondering if they newer SRAM chips are compatible with Teensy Audio
VTI7064MSME
https://datasheet.lcsc.com/szlcsc/Vilsion-Tech-VTI7064MSME_C139966.pdf
LY68L6400SLIT
https://datasheet.lcsc.com/szlcsc/Lyontek-Inc-LY68L6400SLIT_C261881.pdf
both with 64Mbit Serial SRAM (or Pseudo SRAM)
if yes this memory could be a serious addon for the Teensy Audio
Will it work? Yes and no.
#1) They require a bit of startup work. You must hold SCLK low and CS# high during power on sequence, then issues a couple custom commands to reset the device. Not a big deal but you don't do this on conventional SRAM parts.
#2) These are conventional DRAMs wrapped in a SPI interface. Since DRAMs cells decay over time, they need to be periodically refreshed, this refresh blocks regular operations, and this refresh is needed quite frequently. Both those parts use the rising edge of CS# to trigger the refresh operation. If you leave CS# low too long during a burst the memory will not refresh and will start to corrupt it's contents.
So how long can you burst for? One of those parts has max CS# low for 8 us, the other is 4 us. At 8 us, a 20 MHz clock is 50 ns. This means you can only burst for 8000/50 = 160 SCLK cycles. It takes 32 clocks to start a command plus 8 bits per byte after that. So your bursts are limited to about 16 bytes of data. If you're cool with that, you're good.
So, if you tend to issue one write or read per SPI.beginTransaction()/SPI.endTransaction you won't notice. But that is also a VERY slow inefficient way to use SPI. If you transfer more than one byte, you must be very careful not to exceed the max transfer time. You must also account for any idle time the processor puts between calls to SPI.transfer(). If you are using the SPI DMA capabilties, you must limited your burst size accordingly.
Practically speaking, for high-performance audio applications, you really want to use DMA to burst audio blocks to and from the memory and you probably want to do this for an entire audio block which is 256 bytes for the standard 128 samples. So you need to be triggering a lot of DMA transfers just to copy a single block of audio.
So yeah, they should work with some pretty big caveats.