flat arrays, flat strings, flat variables

I published the current status of the SPI DMA driver at https://github.com/andiy/espruino.git

It's important to have in mind, that DMA is only of advantage when sending a minimum amount of data. Below are some benchmarks to have an idea when DMA may be of advantage.

Times [ms] for sending a data buffer of length N:

bytes | native write | writeInterlaced* | writeInterlaced$*
----------------------------------------­------------------
  20k | 42.0 |  4.2 / 18.4 | 3.0 / 18.0
  10k | 22.2 |  4.2 / 11.8 | 3.0 / 11.4
   1k |   4.1 |  4.2 /  9.9 | 3.0 /  8.7
 0.5k |  3.0 |  4.2 /  9.9 | 3.0 /  8.7

*) 1st number is the net time for calling writeInterlaced, 2nd number is the total transmission time

CONCLUSIO:

• writeInterlaced() overhauls native write() at 1k+ bytes
  
• writeInterlaced$() overhauls native write() at 500+ bytes
  
  
  

When sending a small buffer of 1, 2 or 4 byte multiple times, the results are as below.

QSPIx.writeInterlaced( buf, N); // is compared with 
SPIx.write({data:..,count:N});

CONCLUSIO:

• 1 byte buffer: advantage for writeInterlaced at N > 1800
  
• 2 byte buffer: advantage for writeInterlaced at N > 3000
  
• 4 byte buffer: advantage for writeInterlaced at N > 3500
  

1 Attachment