[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

RE: Serial communication without DMA/FIFO. (Low latency)



Hi,
 
>We are implementing an application that communicates over a serial port with mostly small double byte bursts and sometimes a burst with 20-40 bytes.

If you are implementing this in userspace it will not be enough to make the kernel latency "infinite fast". The 
average case may be good but the worst case is bad.

>I´ve found the CONFIG_ETRAX_SERIAL_FAST_TIMER in serial.c. What progress could i expect if defining that?? 

When waiting for characters there will be a timer that expires each 4 * character_time
 
>In one answer there was some talk about a future effort to make it possible to disable DMA on certain serial ports. Is that implemented??
 
No, but it should be pretty easy.
 
/Mikael

-----Original Message-----
From: owner-dev-etrax@xxxxxxx.com]On">mailto:owner-dev-etrax@xxxxxxx.com]On Behalf Of Henrik Löfgren
Sent: Wednesday, February 05, 2003 3:32 PM
To: dev-etrax
Subject: Serial communication without DMA/FIFO. (Low latency)



Hi, 

We are implementing an application that communicates over a serial port with mostly small double byte bursts and sometimes a burst with 20-40 bytes.

That means that we need low latency, i.e. using the serial port without DMA & FIFO. 

I´ve seen some messages here for this subject earlier and have got some hints like changing the CONFIG_ETRAX_SERIAL_RX_TIMEOUT_TICKS value from 5 to 1.

But this is not enough for us so i wonder if anyone out there has some more tips?? 

I´ve found the CONFIG_ETRAX_SERIAL_FAST_TIMER in serial.c. What progress could i expect if defining that?? 
In one answer there was some talk about a future effort to make it possible to disable DMA on certain serial ports. Is that implemented??

Or do i have to write/change the driver at my own?? 


I´m using Devboard LX ver. 2.1.0 and Linux kernel 2.4.14. 


Thanks in advance // Henrik Löfgren