I am working on a custom configuration controller that configures a Spartan 3 through SelectMap and verifies the configuration through readback.
Configuration is simply writing the .bin file into the S3, no problems there.
The trouble starts when I want to give the readback commands the the FPGA - al commands are ignored completely, even though I am using the same code to write to the device. I'm currently just trying to issue a SHUTDOWN command to the FPGA, to see if anything happens.
I've checked (and rechecked) that the data appears on the D0-D7 pins of the FPGA (byte swapped), with CCLK merrily running along, CS_B=0, RDWR_B=0, and I set persist=yes in bitgen.
The S3 datasheet has an interesting flowdiagram (fig 23, p37) that show reconfiguration starting with "prog_b low after power on", then "prog_b high" to avoid clearing the configuration. What is happing there?
Is there anything I'm missing? Some command (on CS_B/RDWR_B perhaps?) that will make the FPGA aware of my intentions?
Any suggestions will be greatly appreciated.