[Gumstix-users] timing problems with gpio-event

[Sébastien S. <seb...@zh...>]

Hello,

I thought it would be possible to work faster... perhaps I missed one 
important thing.

My goal is to transfer USART data from the robostix to gumstix through 
the TWI (I2C) interface.
When the USART buffer is full, it sets the RXC0 interrupt flag. Robostix 
immediately set PE2 to tell gumstix, it has to get some data. Gumstix 
then open a basic I2C communication to fetch 2 bytes (the USART data + 
something else) using I2cReceiveBytes(i2cDevice, rcvBytes, 2).


As you can see on the above picture, the time between RXC0 is set (also 
PE2... 6 CK later) and the TWI interruption begins is bigger than the 
time interval between two RXC0 (320 us... MIDI signal)... also too long. 
My C code on the gumstix has only 2 lines: read(gpioEvent,...) and 
I2cReceiveBytes(i2cDevice...). The gpio-event is 69 : r : 0.

By the way, I find the TWI communication too long, too: for 1 address 
and 2 data bytes @ 400 KHz, it should be < 100 us and it has more than 
200 us. Is actually 400 KHz default it the i2c-api? Or are there more 
than 3 bytes on the line?

...I guess my question is for Dave once again ;-)

Thanks, Sébastien