I plan to immigrate FluidSynth to CORTEX-M4. Could anyone please give me some
hints?
The Cortex-M4 system I am going to use: 1MByte flash code memory. 192KByte
internal SRAM, with FPU, 168MHz, 32MByte external parallel NOR flash (for
soundfont). Is it possible to immigrate Fluidsynth to cortex-M4 with these
limits (64 polyphony)?
I've tried to use optimized cortex-m4 ASM to replace FluidSYnth's lowpass
filter, linear interpolation, reverb, chorus. And I also tried to reduced the
memory needed down to 240KBytes. At this moment, without concerning the low
speed of reading external flash (soundfont), it looks that 192KByte, 168MHz
limit would be OK.
However, the low speed of reading external flash seems to be a big problem:
the flash IC is 90ns, which means you can read 16bits (1 sample point) every
90ns. To make a 64 polyphone rendering, and output at 44.1kHz, for each output
sample, you need to read at least 64*2 samples (if linear interpolation is
used), this is 128*90ns=11.52us, which is already 50% time of the sample period
of 44.1KHz. So, I am afraid I will have to use DMA to do the readings to the
audio samples, so that rendering and transfering audio sample data at the same
time. This will need some more (maybe 10KBytes) memory buffering space, and
increase the complicacy. I wonder if it is really the only choice here to do
DMA for transferring audio sample data?
Does anybody here have similar question/experience? And what's your solution?
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