AM335x memory map UARTx bus error

Hi all,

I’m using the BeagleBone Black board with angstrom Linux with 3.8.13 kernel.

SD card boot.

My goal is to send/receive files via a serial ports UARTx. A BBB send the file and another one recives it, both on UART2 without capes. By now i’m using some available protocols like lerz and lsz.

It works. Furthermore, as specified at page 3964 of the MPU tecnical reference manual (spruh73j.pdf) december 2013 revised, the highest available bit rate without errors is 3Mbps.

It’s Very fast but … there’s a very high cpu usage when a big file is moved from BBB to other one!

For example, a 700MB file size , at the receiver side ,shows a consumption of almost 98%. On the transmietter side , about 25%.

In my opinion , the processor is not exploiting the benefits of the DMA.

I have found a register on the memory mapping of the UART2 that allows to set the DMA mode.

So i have tried to check the status of the register with the devmem2 (same as mmap in C ). But i got this response

root@beaglebone:/sys/class > devmem2 0x48024008
/dev/mem opened.
Memory mapped at address 0xb6f10000.
Bus error

I have never seen this problem with gpio bank! It works properly with that peripherals.

Can anyone help me? or suggest me another way to check the registers properly.

Thanks in advance