Re: coldfire uart question

[Finn Thain <fthain@telegraphics.com.au>]

On Sun, 15 Oct 2017, Angelo Dureghello wrote:

> Hi all,
> 
> i was trying a file transfer with xmodem-1k and uClinux "rx" on the 
> mcf54415 stnmark2 board side.
> 
> This using a recent mainline kernel:
> / # cat /proc/version
> uClinux version 4.14.0-rc4stmark2-001-00118-g811fdbb62a9d
> / #
> 
> So, as per xmodem-1k, i send 3 bytes header, a 1024 bytes block, and 2 
> bytes crc16. But "rx" timeouts waiting the block.
> 

What is the fastest baud rate that will work? 

> Adding some traces to "rx", it timeouts since some bytes (5 to 10) 
> randomly positioned in the block are not received. Of course they have 
> been sent (scope checked).
> 
> The same 1024 bytes transfer in u-boot (y-modem) always succeed.
> 

Does u-boot need to do any retransmissions? (If it polls the UART, it 
could probably avoid any fifo overflow.)

You may also want to try lrzsz.

> Since mcf54415 has a 4 slots RX fifo UART,

Ouch. At 115200 baud, that FIFO overflows after about 347 microseconds. If 
the kernel takes one interrupt per 4 bytes, you're looking at thousands of 
interrupts per second. Add a little unexpected interrupt latency (say, 50 
microseconds) and the next byte gets lost.

-- 

> i was wondering if the mcf.c uart driver is not fast enough to read the 
> data, or, where the "linux" limitation could be.
> 
> Regards,
> Angelo Dureghello
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