14 Nov
2011
14 Nov
'11
7:37 a.m.
On 11/13/2011 10:53 PM, David Riley wrote:
I should point out too that the VGA DAC is nothing
more than a
resistor ladder for each channel with 4 bits (plus pins out for sync
signals).
Right. An example for modifying a Xilinx board for added colors is here.
http://www.fpgaarcade.com/displaytest.htm
For me, if it's already done, pins already reserved for the task,
resistors already on the demo board, it's one thing less to worry about.
On the same site, I'm really excited about the FPGA replay board that is
selling soon.
http://www.fpgaarcade.com/common/replay_overview.jpg
It is in essence a big FPGA with memory, and a bunch of other hardware
on the board for running existing cores of retro-machines.
Well, DDR is a pain in the ass. It has a lot of timing
constraints
(including a minimum clock speed on non-LPDDR parts because there's a
DLL for aligning the data that has a minimum speed) that are very
hard to match.
And there are board/trace routing issues that you must also take into
account.
Regular SDRAM (which is what's on the DE1, at
least)
doesn't have any requirements like that as long as you refresh often
enough. Even the "commands" to the controller on the chip follow the
same pattern as their non-synchronous counterparts. I believe Terasic
even includes some free-as-in-beer core to make it behave much like
SRAM on their site and in the materials that come with the DE1.
Can you please point me to this? I have a DE0 as mentioned, and I
actually use a modified FOSS core designed for the DE2, which works fine
on the DE0. I'd rather use an official or better-vetted solution.
I downloaded the DE1 CDROM from Terasic and I don't see it. Their "using
sdram with verilog" sounds really promising, until you figure out that
they actually create a NIOS II core with the memory controller, and then
have you access the memory from verilog through that core.
I even emailed support about this, and they said, "sorry, yes, only
through NIOS."
What is frustrating about Terasic Support is that when I found a problem
with VGA support where a certain pin does "double duty" as both a
VGA-pin and a programming pin, the default Altera software fatals out
with default configuration. You need to change something to use the VGA
connector. SO I email them, point out the issue, point out the
resolution, and told him to add it as an FAQ. I probably took me an
hour or so to find a working resolution on my own. They've failed to
ever add it to their FAQ......
- Dave
Keith