From mboxrd@z Thu Jan 1 00:00:00 1970 From: Grant Edwards To: Gary Thomas Cc: ecos Subject: Re: [ECOS] ARM vectors.S question Date: Wed, 27 Oct 1999 07:01:00 -0000 Message-id: <19991027090116.B14874@visi.com> References: <19991026204215.B27067@visi.com> X-SW-Source: 1999-10/msg00098.html On Wed, Oct 27, 1999 at 06:21:41AM -0600, Gary Thomas wrote: > > Perhaps my prejudices from doing 15 years of embedded systems are > > showing, but I don't see how any system could be laid out this way. > > Perhaps I don't understand how the power-up reset works in the CPU? > > No, we would never assume that RAM survives a reset :-) > > Most hardware that has RAM at 0x0 and the ROM somewhere else has shadow > magic that makes the ROM appear at 0x0, either for a fixed number of cycles > after reset or until a control latch is reset. Ah yes, about 20 years ago I had an S-100 bus Z-80 bus system that did the shadow rom for X cycles after reset trick. I had forgotten about that. > Firstly, you should consider working from the public CVS repository. This > has the latest stuff in it, including much work that lets items such as > this be specified in platform specific files, not directly in "vectors.S". OK, I'll take a look at the CVS tree -- having to modify what were supposed to be platform-independant files made me think that I was headed in the wrong direction. Are there semi-stable CVS snapshots, or is a guy pretty much rolling the dice when using sources from the CVS tree? > Are you using the CVS version, or some other source release? I'm using the 1.2.1 official release. > I'll try and provide help/guidance with whatever changes you need. > Note that there are other places than "vectors.S" that expect low memory > to be writeable so vectors can be updated. Unless you can take the > "remap" route, there will be other considerations. Thanks. That's a very useful tip. I should be able to go either way: remapping ROM/RAM in startup code or having ROM vectors go through RAM. Initially I was thinking of sticking with the ROM vectors, but it sounds like remapping might be a better idea. > > I must say that the ARM load/store instructions are about the coolest > > I've seen since the PDP-11. > > I shudder to think what you've been working with... Mostly the usual crop of embedded architectures (8086, 8051, 68HC11, 68332) and the TI TMS32C320 DSP for a while [it was wierd having sizeof (everyting) == 1]. -- Grant Edwards grante@visi.com