Sorry, guys, I have no idea whether it makes you feel uncomfortable the way I ask questions. If yes， I apologize. But, I really don't understand the way uboot branch to nor flash, branch to ram. I have read the source code in the 83xx/start.S file for many times, and I have looked up the archives of uboot mailinglist in Dec. 2010. I found that the way start.S is written is for position independent code. I really know little with this kind of impelmentation. Is there anyone who is willing to give some guidance, such as website? Thanks a lot. Best Regards, Shawn
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From: programassem@hotmail.com To: u-boot@lists.denx.de Subject: problem with mpc837x start.S Date: Wed, 27 Jul 2011 06:21:13 +0000
Hello, boys and girls, my name is shawn Bai. I am new here and hope not disturb you. Although I have not posted before, what you do is very helpful to me to understand what is bsp, how it runs, and so on. I don't know whether the question below is mentioned or not before. If yes, do you mind telling me where I can find the answer. Thanks in advance.
The question is about arch\powerpc\cpu\83xx\start.S. the demo board I use is MPC837xERDB, there is 8MBytes Nor flash on it. by default, uboot is booted from lower address, it means BMS field in HRCW is 0, which will affect value of MSR[IP] later. First instruction locates at _start label in uboot. Before first instruction runs, hardware reset configuration word will be loaded to make some basic configuration. Before branching to MONITOR_BASE+in_flash using blr instruction， size of LCS0 is inflated to 4GBytes， and eLBC access window 1 is configured with BAR MONITOR_BASE, and SIZE 8MBytes. After this is done, blr to MONITOR_BASE+in_flash. after branching to MONITOR_BASE+in_flash, LCS0 BAR is modified to MONITOR_BASE, and its size is configured with 8Mbytes again. This is what I know. But the problem which is confused to me is after reset, the default value of LCS0 BAR is 0x0000_0000, and its size is 8Mbytes. In order to branch to MONITOR_BASE+in_flash, inlarge Nor flash to 4GB, and configure eLBC access window 1. But the actual size of Nor flash is 8MB , even after inlarging it, where (MONITOR_BASE+in_flash) points to? why? why does branching to in_flash need absolute address? and make absolute address like this? I rack my brains, but there is no result. Do you mind showing me a way? Thanks very much.
Shawn Bai
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