# FPGA; reconfigure from SPI flash

I have designed a Xilinx Spartan-6 PCI card with SPI configuration interface (please check Figure 2-12 of ug380.pdf user guide). I can program the serial flash through JTAG cable, I can also modify/program the serial flash through the PCI bridge chip, for field upgrade purposes. Unfortunately I forgot to connect one of the GPIO pins from the PCI chip to the FPGA's PROGRAM_B pin, now I have to power cycle the computer to restart the configuration.

Is there a way that FPGA firmware can "FORCE" the configuration process without external assertion?

• Maybe the ICAP interface will let you do it? xilinx.com/support/documentation/user_guides/ug380.pdf search "Internal Configuration Access Port" – Some Hardware Guy Sep 11 '15 at 21:16
• @SomeHardwareGuy: thanks for your advice. I implemented the logic and it's working just fine. I had to accept the answer from alex.forencich as he posted his notes in the answer section. Thanks! – Ali Oct 8 '15 at 20:31

This question has been stuck in the back of my head for a while and I just stumbled across the answer in the Virtex 6 configuration guide and then cross-referenced it to the Spartan 6 configuration guide. See the IPROG reconfiguration section in UG380 on page 128. This page includes the sequence of words to write to the ICAP_SPARTAN6 interface to emulate a PROGRAM_B assert from user logic. This is designed for re-starting configuration with a different base address if you have multiple FPGA images stored in the same flash chip. I will reproduce the sequence here for posterity:

1. send sync word
2. program GENERAL1,2 and GENERAL3,4 registers with new bitstream address + flash read opcode and 'golden' bitstream address + flash opcode.
3. send IPROG command

It may be possible to skip step 2 and just send the sync word and IPROG command to use the default values for the start addresses.

Byte sequence:

FFFF dummy word
AA99 sync word
5566 sync word
3261 write GENERAL1
XXXX start address [15:0]
3281 write GENERAL2
XXXX opcode and address [23:16]
32A1 write GENERAL3
XXXX start address [15:0]
32C1 write GENERAL4
XXXX opcode and address [23:16]
30A1 write CMD
000E IPROG
2000 NOP


You might be able to get away with:

FFFF dummy word
AA99 sync word
5566 sync word
30A1 write CM
000E IPROG
2000 NOP

• it's funny, I was reading that document half an hour ago and right now I'm in the middle of implementing the same thing. Thanks a lot, I'll let you know how it goes. – Ali Sep 21 '15 at 22:06
• Good to hear. Did you end up using the short sequence, or did you have to use the longer one? – alex.forencich Oct 8 '15 at 20:41
• I tried to strip down some of the steps from the longer one. I can only recall that your suggested short sequence didn't work, a couple of more steps had to be included but I decided to implement the whole thing in case I need it in future. – Ali Oct 8 '15 at 20:57
• Hmm, that's interesting. Nice to know it works, though. – alex.forencich Oct 9 '15 at 6:08