Re: [Discuss-gnuradio] setting registers

[Matt Ettus]

Brian Padalino wrote:
> On 7/16/07, George Nychis <address@hidden> wrote:
>> So I think what Leo is getting at is how to actually perform the read or
>> the write to a register for the C/S packets.  For instance we have the
>> read/write register commands where the application says read from
>> register X or write this data to it.
>>
>> This would pertain to OP_WRITE_REG, OP_WRITE_REG_MASKED, OP_READ_REG,
>> and OP_READ_REG_REPLY:
>> http://gnuradio.org/trac/browser/gnuradio/trunk/usrp/doc/inband-signaling-usb
>>
>>
>> I'm assuming what Leo is wondering, is when I pass him register 3 for
>> instance, how he can actually perform the read or write.
>
> Major surgery.  Disconnect the I2C pins between the FX2 and the FPGA
> logic (float the pins coming in, and ground the pin going out?).  Then
> every register has to be put into a register file which the C/S state
> machine has the ability to read/write, and create input ports for each
> of the modules which have registers associated with them.

FPGA registers are not set using I2C, they are set with SPI.  There is
already a mechanism for reading back values over SPI, but it is only set
up to read back 8 values now, mostly for reading io pins and rssi
levels, but not every register.  See serial_io.v and setting_reg.v

> You may be able to use a spare pin connected to the FX2 to perform
> some weird loopback thing where the host sends to FX2 which then sends
> to the FPGA.  The FPGA notices it must write a register, so it sends a
> special packet back to the FX2 which the FX2 parses after it reads (no
> DMA here) and then performs the I2C write, but that is a big old mess
> too.

No hardware modifications necessary
.

Matt