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boot pb1500 from flash through 16-bit data bus?

To: "linux-mips" <linux-mips@linux-mips.org>
Subject: boot pb1500 from flash through 16-bit data bus?
From: "Wang Zaifang" <yikok9@yahoo.com.cn>
Date: Tue, 4 Nov 2003 10:13:09 +0800
Original-recipient: rfc822;linux-mips@linux-mips.org
Reply-to: yikok9@yahoo.com.cn
Sender: linux-mips-bounce@linux-mips.org
hi, 
  Does anyone have experience on writing 16-bit booting code for PB1500?
  I'm working on a customized au1500 board that has puzzled us for serveral 
days, :-( The board is designed to boot from flash using 16-bit data bus, 
however it seemed that the code we stored in the flash does not run at all. 
There might be some errors in our design, so we turn to the PB1500 eval-board.
  I wrote a piece of testing code that sends 010101... series to GPIO[0] 
continuousely after reset. The code runs well when the SRAM data bus is set to 
32-bit width, i.e. a square waveform appears on GPIO[0]. Then I burn the code 
into flash through YAMON, assuring the code only reside in one flash chip of 
the two. Content of the flash looks like this in YAMON:

YAMON> dump bdc00000

BDC00000: 90 B1 00 00 08 3C 00 00 80 80 00 00 09 34 00 00  .±...<.......4..
BDC00010: 2C 00 00 00 09 AD 00 00 FF FF 00 00 09 34 00 00  ,....-.......4..
BDC00020: 00 01 00 00 09 AD 00 00 00 00 00 00 09 24 00 00  .....-.......$..
...

  Each instruction word is split into two half-words, and put into lower 
16-bits of two words. Then I reset the PB1500 board, switch S15 to set the SRAM 
data bus to 16-bit mode, switch S13 to boot from the specified flash chip. But 
the code will not run, even after I swap the byte-order and the halfword-order.

  Any advice will be appreciated, :-)

        Wang Zaifang
        yikok9@yahoo.com.cn
          2003-11-04
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