Using propeller standard SPI interface

dr hydra

Using two propellers (A and and a SPI interface...how fast (or how many bytes per second) can you send data between them...for example...how long would in take to send 4,000 byte from Propeller (A) to Propeller (B)?

Mike Green

There really isn't a "standard" SPI interface, but it's one of a variety of clocked serial interfaces. Using PASM, this could be quite fast, a megabit per second or more is reasonable. There are ways to use the cog counters to do the clock generation that are somewhat faster.

dr hydra

what about in slave mode....how fast the propeller receive data....plus get that data from a cog to the hub memory...ex...receive 4000 bytes

jazzed

dr hydra wrote: »

what about in slave mode....how fast the propeller receive data....plus get that data from a cog to the hub memory...ex...receive 4000 bytes

Less than 0.1 seconds ;-)

One could get a more accurate estimate by coding it though.

pseudo-code assuming SPI with CS, CLK, RX, TX

:doreceive
if no chipselect, exit
:getbyte
wait for clock
if clock timeout, exit
save bit
repeat :getbyte
adjust rxqueue pointers
save byte to hub
repeat :doqueue
:exit

So, if the above algorithm results in about 24 instructions and the byte loop is about 4 instructions, then you might get a byte every 50 or so periods 50 instructions * 50ns = 2.5 us / byte or 400KB/s ... which is about 0.1 seconds for 4000 bytes ;-)

Demonstrates why having a hardware helper is useful no ?

Peter Jakacki

Why don't you just use async rather than SPI because there is no need to generate and synch to a clock. I have no problem transmitting and receiving at over 3M baud and certainly at 2M baud at 100% throughput (start bit, 8 data, 1 stop bit), so that's 200,000 bytes/sec or for 4,000 bytes that will take 20ms.

If you can make it synchronous though then you could transmit and receive at up to 14.5Mbit/sec (BeauNet) so that's less than 3ms for 4,000 bytes.