You can consider some SPI flash chips from MXIC, eg MX25L1605, which
feature additional 4kbits eerom on the same chip.
Thanks for the very interesting hint !
But with this project we need some 256 K of nonvolatile data memory, so
an additional flash chip seems appropriate (ans seems to cost less than
$ 2).
I suppose there is an MTD (or similar) driver that converts the SPI
flash chips to be block devices and that I can mount (e.g.) CRAMFS
for the stuff to be copied into RAM and (e.g.) JFFS2 for dynamically
used data.
You can use EPCS MTD chip driver, which accesses SPI flash through
FPGA configuration port.
That is what I hoped. I'm not sure whether the "data" chip should be
attached to the same SPI bus as well, or if a second SPI interface
should be provided for same.
We prefer initramfs instead of cramfs or romfs, as it is easier and
used widely on latest Linux desktop. It is used by default in
uClinux-dist nios2 arch.
I understand that the initramfs method is more complicated but offers
some advantages. Of course I'll use it if it's the default in the
distribution I hopefully once will obtain.
I think I should not run much code or read many files from the "program"
flash, but all that is needed should be copied to the RAM when starting.
I suppose after starting the Kernel the root file system is copied from
a partition of the program Flash into RAM. I suppose this can be done
using the initramfs method.
I want to have (at least) one more partition in the flash that should
contain a real file system (jjfs2 ?). The initial user mode stuff should
create an file system in RAM and copy the content of that partition in
the flash there. But the files in the flash should be writable by normal
user land programming (for upgrade purposes).
You can use JFFS2 for user data, but it requires more space than
4kbits. For simple user data, you can access directly over MTD device.
I understand that MTD provides a block device. Is id "good behavior" for
user mode programs to directly read/write from/to block devices ?
You may find more related on Nios Wiki. I do recommend uClinux-dist
over Microtronix's.
I'm working together with Ben (F A E of my dist ribu tor) on that.
Hopefully he'll come up with a workable solution based on the 2.6.23
uClinux-dist.
BTW, I have work out the way to debug apps on uClinux. Eclipse CDT
should not be far.
That is exactly what I want. I suppose you did meet Ben somewhere around
here. Maybe you can help him find something decent to offer us, so that
we can avoid Microtronix. We really want to (buy development hardware
and) start working on that in January.
OTOH, Microtronix did provide some Eclipse plugins that I did see
working with Quartus 7.x (which I need to use as we intend to go with
the Cyclone III). Can these be used or will someone provide similar
plugins ?
Thanks for all your work !
-Michael
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