Subject board has two 2C devices and a 3C device in a serial config chain. The
2C device's MSEL pins are jumper configurable to AS (for "self-config") or PS ("Software Config") config mode. The other two FPGAs, downstream from the first 2C device, are strapped for PS mode only.A MAX-II CPLD sits on the DCLK, DATA0, nCONFIG, nSTATUS, nCE, nCEO, and CONF_DONE signals to "monitor" configuration in "Self-Config" mode, and to control (drive) these signals in "Software Config" mode.
When powering up with the jumper set to "Self-Config" - where the FPGAs self-config from an EPCS64 serial config ROM - the FPGAs config just fine (note: the first device in the serial chain, a 2C5, is the AS mode config controller).
When powering up with the jumper set to "Software Config" (i.e. MAX-II CPLD driving the configuration lines under SW control), the FPGAs do not come alive. The nCEO outputs from each of the three FPGAs is asserted LOW, which I interpret to be solid evidence that the FPGAs are all "configured", but CONF_DONE never goes high. And yes, we send lot and lots of extra config clock pulses to move the devices from "configured" to "user mode". Still no CONF_DONE. But wait, there's more...
I can power up the board with the jumper set to "Self-Config" (as above), and the FPGAs configure and "come alive" (i.e. they respond to bus accesses) as expected. Then I move the jumper to "Software Config", hit the "RESET" switch (which "warm boots" the board without cycling power), and the FPGAs then configure under software/LOBO control at every config clock speed I've tried up to 33.33MHz.
So what gives? Why does PS config *not* work without first configuring via AS mode? Why doesn't PS fail (or succeed) *all* the time, given that the logic and config code doesn't change?
It sure looks like I'm lurking in the dark corners of some unwritten spec sheet that would express all the "other" requirements for successful config. I'm not hopeful that Altera will be forthcoming with support on this one.
What "state" is cleared or changed by the AS mode config to then allow the device chain to successfully config in PS mode ?
Boy, I could sure use a life-line on this one. If anyone has some WAGs, I'm listening !
- Bob Elkind