Configuring the fpga, Functional discussion of fpga operation, Cobranet™ ev-2 – Cirrus Logic EV2 User Manual
Page 18
Rev. 2.1
18
CobraNet™ EV-2
Configuring the FPGA
The FPGA is configured from data that is stored in the upper 16kbytes (0xC000-0xFFFF) of
the microcontroller’s Flash Program Memory. The microncontroller code for configuring the
FPGA uses express mode which writes byte-wide data to the FPGA. Refer to the Xilinx
Spartan XL family data sheet for more information on the express mode configuration
operation. The address used for writing configuration data is 0x8800.
Functional Discussion of FPGA Operation
Routing of Audio Data
The routing of audio data is achieved by a simple 8 to 1 multiplexing operation; for each
audio destination three data bits in an a register in the FPGA select the source. For
example, the three data bits in the D/A audio routing register determine which audio
source is selected to appear at the analog outputs (J401). Table 7 on page 18 shows the
definition of the data bits and the respective audio source.
microcontroller data bit
AD2 AD1 AD0
Audio Source
0
0
0
CM SSI 0
0
0
1
CM SSI 1
0
1
0
CM SSI 2
0
1
1
CM SSI 3
1
0
0
ADC
1
0
1
AES3 Input
1
1
0
ADC (low latency, Rev D only)
Otherwise same as ADC above.
1
1
1
Sine wave
Table 7: Definition of Audio Routing Register Bits