Hardware SPI ~0.85ms delay before sending data

[blark]

I have a question about delays that I'm experiencing with hardware SPI. I have the following code which sends 16 bytes of data:

Code: Select all

vspi = SPI(2, 1000000, polarity=0, phase=0, bits=16, firstbit=0, sck=Pin(18), mosi=Pin(23), miso=Pin(19))
test = bytearray(16)
ss.off()
vspi.write_readinto((0xff).to_bytes(16, 'little'), test); 
ss.on()

Each time I send this sample frame it takes what seems an excessively long time to actually start the SPI transaction after bringing the SS line low. Logic analyzer screen cap:



By comparison it only takes 78 uS to bring the SS line back up afterwards. Any ideas how I can speed this up? I need to send 512KB with SPI and a near 1ms delay for each transmission adds up.

Thanks!

[pythoncoder]

The ESP32 is not renowned for low latency but you might gain a little by cacheing the send bytes:

Code: Select all

wb = (0xff).to_bytes(16, 'little')  # Can be done once only
vspi = SPI(2, 1000000, polarity=0, phase=0, bits=16, firstbit=0, sck=Pin(18), mosi=Pin(23), miso=Pin(19))
test = bytearray(16)
ss.off()
vspi.write_readinto(wb, test); 
ss.on()

[blark]

Not much improvement at all from caching bytes. I found another thread on this that states there is a lot of data checks and SPI setup going on in the background. It seems like something that could possibly be optimized.

I guess I will use large transfers (of about 1KB at a time) so I don't experience much overhead from SPI setup when transferring the data.

[blark]

I'm still kind of hung up on this, anyone know if it's possible to use Viper to directly access the HW SPI peripheral?

I cranked the ESP32 frequency up to 240MHz and it's still taking a long time between SPI messages. In contrast the STM32 running at 84Mhz that I am sending 1000 bytes of data to processes it in 35.67us. Hopefully there is a way to reduce the pauses, anyone? Thanks in advance!