Qsys, How do you determine the Address for an Avalon-MM Block?

Take a close look at the documentation for mmap. It gives you a pointer to where in your address space it put the physical address you gave it. Say the offset to the register you are looking at is 4 from the start of your device. You need to use a pointer value that is value mmap gives you + 4. Beware of C pointer arithmetic as well. Print out the value returned by mmap and of your pointer and wait long enough for it to get to the screen before you access your device. Confirm that it is using the correct value.

Ok, so this is a picture of how the memory was assigned in Qsys: http://imgur.com/iorpxmq

I didn't have time to look at it in detail but I did find a few things:

• You shouldn't use a struct to define hardware register layouts. You aren't guaranteed that the compiler will layout memory as you intended. I'd recommend using# define or const to define byte offsets to your registers.

• The offset for mmap is wrong. It needs to be the physical address of your registers. I don't recall how to calculate this, so look at some linux examples for SoC. Note that it isn't the address in QSYS. That doesn't take into account the starting address of the interface you are using.

• Your HW_SPAN is too big. Use the smallest multiple of the linux kernel page size (usually 512) that will hold all your registers. It would be 1*512 for your application.

• You shouldn't use a struct to define hardware register layouts. You aren't guaranteed that the compiler will layout memory as you intended. I'd recommend using# define or const to define byte offsets to your registers.

 typedef struct __attribute__((packed))  {
     uint16_t Control,
             ClockPreScaler,
             MatchRegister,
             MatchChannel0,
             MatchChannel1,
             MatchChannel2;
} PWM_t; 

• The offset for mmap is wrong. It needs to be the physical address of your registers. I don't recall how to calculate this, so look at some linux examples for SoC. Note that it isn't the address in QSYS. That doesn't take into account the starting address of the interface you are using.

• Your HW_SPAN is too big. Use the smallest multiple of the linux kernel page size (usually 512) that will hold all your registers. It would be 1*512 for your application.

So far I've found some errors in my FPGA design, such routing the wrong CLK nets. ( side note: who does the default template for the development board and duplicates the clock nets and instantiates the wrong ones in the top level module?!?!)

Look at the registers in HPS for the interface to fpga fabric you are using. The interface should be initialized when Linux boots, but there is a lot that can go wrong and cause the bridge to not be initialized.

There should be mention of the bridge(s) in the text bthat print when booting

This is what I got:

altera_hps2fpga_bridge fpgabridge.2: fpga bridge  registered as device hps2fpga         
altera_hps2fpga_bridge fpgabridge.2: init-val not specified                                       
altera_hps2fpga_bridge fpgabridge.3: fpga bridge  registered as device lwhps2fpga     
altera_hps2fpga_bridge fpgabridge.3: init-val not specified                                       
altera_hps2fpga_bridge fpgabridge.4: fpga bridge  registered as device fpga2hps         
altera_hps2fpga_bridge fpgabridge.4: init-val not specified

root@socfpga:/sys/class/fpga-bridge# ls 
fpga2hps    hps2fpga    lwhps2fpga
 root@socfpga:/sys/class/fpga-bridge# cat */enable
1
1
1