IORD and IOWR issues

[Altera_Forum]

Hello there, 

 I am struggling to understand a simple write and read with the nios processor.  With qsys, I have setup a simple testcase where a nios (e) with no cache and a PIO are connected. PIO is connected to the external LEDs. With the DE0NAN0 board, I can easily see the LEDs to change to what value I have put on the eclipse program. e.g IOWR(PIO_BASE,0,0xA);  Then, I manually changed the qsys generated pio.led such that  data_out <= {writedata[5:0],1'b1}; instead of  the original data_out <= writedata[5:0];  and ensured that the qsys does not generate the nios and pio again during the compilation.  Afterwards, with eclipse program, I do a IOWR(PIO_BASE,0,0xA); printf("%X ",IORD(PIO_BASE,0));  I was expecting that "10101" in binary from a IOWR of 0xA. However, it reads "0xA".  Can anyone please shed some light what I am doing wrong here ?

[Altera_Forum]

If data_out has the original 6bit data width, you should write 

data_out <= {writedata[4:0],1'b1}; otherwise I think the compiler discards the added bit.

[Altera_Forum]

Nice catch. however it was just a typo I made when writing that post 

 the original version from qsys was data_out <= writedata[6:0];

[Altera_Forum]

--- Quote Start ---   Afterwards, with eclipse program, I do a IOWR(PIO_BASE,0,0xA); printf("%X ",IORD(PIO_BASE,0));  I was expecting that "10101" in binary from a IOWR of 0xA. However, it reads "0xA".   --- Quote End ---   Make sure Nios doesn't perform a cache access instead of the actual IORD access. Flush the cache between the two instructions or force IORD to be uncached by setting address bit 31.

[Altera_Forum]

I have  

- verified the logic on the technology map - set address bit 31 as you recommended - on system.h, NIOS2_DCACHE_SIZE and NIOS2_ICACHE_SIZE = 0  still I dont have the expected "10101" in binary from a IOWR of 0xA.  HW: data_out <= {writedata[5:0],1'b1};  Observed behaviour on both the LEDs and with IORD suggest that the implementation is data_out <= writedata[6:0];  Do you have any other idea how to debug that ?

[Altera_Forum]

I would recommend you then to verify if the correct .sof file is being uploaded.