PC104-FPGA newbie questions

Hello - I'm venturing into a PC104 project and have few questions to
start off. I have no experience with PC104 whatsoever.

The goal is for a PC104 module to talk to another board with an FPGA on
it. Questions are:

1. Can I use any version of Linux on the PC104 ?

2. To save time, I hope to use the PC104 in 8-bit mode. Does anyone see
a problem with this approach ?

3. Does anyone have experience writing verilog on the FPGA to talk to a
PC104 ? I hope CLK, Addr, Data are all that's critical. What other
complexities should I envision ?

4. I presume the Linux driver on the PC104 can issue outb() & inb()
equivalent calls to send/receive data to/from the FPGA. Is this correct
?

Thanks.

In news:1129691522.750715.111960@g14g2000cwa.googlegroups.com,
inova <inova27@gmail.com> typed:
> Hello - I'm venturing into a PC104 project and have few questions to
> start off. I have no experience with PC104 whatsoever.
>
> The goal is for a PC104 module to talk to another board with an FPGA
> on it. Questions are:
>
> 1. Can I use any version of Linux on the PC104 ?

I guess you mean a PC/104 board with an x86-compatible CPU.  PC/104 is just 
a form factor.  Yes, you can use any version of Linux, provided you have a 
harddisk or flash module large enough to hold the Linux distribution.


> 2. To save time, I hope to use the PC104 in 8-bit mode. Does anyone
> see a problem with this approach ?

No.  8-bit is the the easiest and slowest mode.  An 8-bit in or out 
instruction takes ~1.5 usec.


> 3. Does anyone have experience writing verilog on the FPGA to talk to
> a PC104 ? I hope CLK, Addr, Data are all that's critical. What other
> complexities should I envision ?

For an I/O-mapped FPGA, you can use SA0-9, SD0-7, /IOR, /IOW and AEN.  The 
I/O cycles you see are not synchronous to any clock in a well-defined 
manner.  When SA0-9 match and AEN and /IOR are low, you have a read cycle, 
and output the data on SD0-7.  When SA0-9 match, AEN is low, and there is a 
rising edge on /IOW, you have a write cycle, and latch the data on SD0-7.


> 4. I presume the Linux driver on the PC104 can issue outb() & inb()
> equivalent calls to send/receive data to/from the FPGA. Is this
> correct ?

Yes.

Karl Olsen

Thanks Karl. Most helpful. Quick follow-up question.

When you say "For an I/O-mapped FPGA ... ", what is the effort involved
? Should something special be done on the FPGA to make it an I/O mapped
FPGA ? Should I be wiring the M/IO# pin on the PC/104 somehow ?

I don't understand how the OS would interpret an external device as an
I/O mapped device.

Thanks again.

Another question on the same topic:

I'm looking at the Linux source for an ISA driver and I see it uses
"request_region()" call to get an address range for the device. For
this call to succeed, are there any requirements from the FPGA ?

How will the FPGA know that it is being addressed ? (Since its the only
device on the PC/104 bus, I guess all signals are being addressed to
it. But I'm curious as to know whether there should be any hardware
setup needed to make the FPGA respond to a specific address range.)

Thanks.

In news:1129706469.853473.306720@f14g2000cwb.googlegroups.com,
inova <inova27@gmail.com> typed:

> When you say "For an I/O-mapped FPGA ... ", what is the effort
> involved ? Should something special be done on the FPGA to make it an
> I/O mapped FPGA ? Should I be wiring the M/IO# pin on the PC/104
> somehow ?

There is no M/IO# pin in the PC/104 bus.  Making an I/O mapped device 
involves no more than the SA, SD, IOR#, IOW# and AEN stuff I described.  The 
PC/104 bus is the same as the old ISA bus, and it is not that complex.


> I don't understand how the OS would interpret an external device as an
> I/O mapped device.

Simply by issuing inb() and outb() instructions to the relevant addresses.

Karl Olsen 

In news:1129707063.446803.78710@g44g2000cwa.googlegroups.com,
inova <inova27@gmail.com> typed:

> I'm looking at the Linux source for an ISA driver and I see it uses
> "request_region()" call to get an address range for the device. For
> this call to succeed, are there any requirements from the FPGA ?

No, this only to ensure that the kernel doesn't try to use the same 
addresses for different devices.


> How will the FPGA know that it is being addressed ? (Since its the
> only device on the PC/104 bus, I guess all signals are being
> addressed to it. But I'm curious as to know whether there should be
> any hardware setup needed to make the FPGA respond to a specific
> address range.)

All signals in the PC/104 bus run in parallel.  There is no automatic 
address assignment in PC/104.  You simply pick an address range (possibly 
configurable by jumpers etc.) that nobody else uses.  I/O range 3F8h-3FFh is 
normally used by COM1, 2F8h-2FFh by COM2, and so on.  It is your 
responsibility to pick an unused range.  Ranges like 200h-21Fh, 220h-23F, 
300h-31Fh, 320h-33Fh are normally good candidates.  In your FPGA, you then 
look at SA0-9, and when they match the agreed-upon range, you have a cycle 
for you.

Karl Olsen