UART RS232 receive missing bytes

[Altera_Forum]

Hi, 

 I have trouble receive bytes of data using UART RS232 port on uClinux running NIOS2 /f. A loopback application was implemented to send 128 bytes hex data from ttyA0 (RS232 port) and receive on ttyA5 (RS232 port). This is a DE2-115 development kit. The IRQ for both port is 1 and 2. I have a JTAG for nios2-terminal, but it's irq is 3. I have disabled the flow control (ctsrts, xon/xoff,etc), but each loopback test I do, I always missing 10 to 11 bytes. However, if I send less than 10 bytes of data, I have higher chance of success getting the same bytes across. If anyone know of this problem and have a solution to it, please kindly let me know what I am missing?  Thanks,  Yeung

[Altera_Forum]

Hi, I had also similar problem : missing bytes in UART. 

 You are treating UART RS232 as interrupts, which are at high priorities. That is quite good.  I don't know uClinux, I guess it employs Hardware Abstraction Layout functions.  Others write their own drivers for RS232  For me, I employ FIFOed UART (in opencores.org)  Search in forum, many thread on that, but I haven't found perfect solution.  Regards

[Altera_Forum]

I'd guess that the kernel has interrupts disabled (or a long interrupt routine) for long enough for you to lose bytes. 

The only real solution is to add a hardware rx fifo to the uart (or rx dma - but that is just a fifo in host memory). With a small OS (aka no real OS at all) you can probably ensure that the interrupt latency is always short enough. But I doubt you'll manage with anything large!

[Altera_Forum]

Hi, 

   --- Quote Start ---   I have experience missing receive bytes using UART RS232 port on uClinux running NIOS2 /f. I implemented a loopback application to send 128 bytes hex data from ttyA0 (RS232 port) and receive on ttyA5 (RS232 port). This is a DE2-115 development kit. The IRQ for both port is 1 and 2. I have a JTAG for nios2-terminal, but it's irq is 3. I have disabled the flow control (ctsrts, xon/xoff,etc), but each loopback test I do, I always missing 10 to 11 bytes. However, if I send less than 10 bytes of data, I have higher chance of success getting the same bytes across. I have heard I need a FIFO MEGAIP for the design but there no current uClinux driver support it. If you know of this problem and have a solution to it, please kindly let me know what I am missing?   --- Quote End ---   At first, please check whether the rx buffer overflow is happend really or not by e.g. 'cat /proc/tty/device/altera_uart' etc. If you want to use an UART IP with FIFO, please check the next page.  http://alterawiki.com/wiki/fifoed_avalon_uart  This IP has the same registers as the normal UART, and maybe we can use the same UART driver. I tested it under the next configuration and at least, it works.  Kazu