mem285.s

Intel XScale PXA255 引导Linux的Redboot 版bootloader源代码！

// #========================================================================
// #
// #    mem285.S
// #
// #    StrongARM EBSA-285 memory setup
// #
// #========================================================================
// ####COPYRIGHTBEGIN####
//                                                                          
// -------------------------------------------                              
// The contents of this file are subject to the Red Hat eCos Public License 
// Version 1.1 (the "License"); you may not use this file except in         
// compliance with the License.  You may obtain a copy of the License at    
// http://www.redhat.com/                                                   
//                                                                          
// Software distributed under the License is distributed on an "AS IS"      
// basis, WITHOUT WARRANTY OF ANY KIND, either express or implied.  See the 
// License for the specific language governing rights and limitations under 
// the License.                                                             
//                                                                          
// The Original Code is eCos - Embedded Configurable Operating System,      
// released September 30, 1998.                                             
//                                                                          
// The Initial Developer of the Original Code is Red Hat.                   
// Portions created by Red Hat are                                          
// Copyright (C) 1998, 1999, 2000 Red Hat, Inc.                             
// All Rights Reserved.                                                     
// -------------------------------------------                              
//                                                                          
// ####COPYRIGHTEND####
// #========================================================================
// ######DESCRIPTIONBEGIN####
// #
// # Author(s):     Red Hat, hmt
// # Contributors:  Red Hat, hmt
// # Date:          1999-07-05
// # Purpose:       StrongARM EBSA-285 SDRAM initialization
// # Description:   SDRAM Initialization for Intel(R) SA-110 21285 Companion
// #                Chip
// #                Intel is a Registered Trademark of Intel Corporation.
// #                Other Brands and Trademarks are the property of their
// #                respective owners.        
// #
// #####DESCRIPTIONEND####
// #
// #========================================================================

	.file "mem285.S"
        .title "SDRAM Init for Intel(R) SA-110 21285 Companion Chip"

#include <cyg/hal/hal_ebsa285.h>

#include <pkgconf/system.h>

	.text
        .align     4

#define ARRAY_0_MODE_REGISTER     (SA110_SDRAM_ARRAY_0_MODE_REGISTER_BASE)
#define ARRAY_1_MODE_REGISTER     (SA110_SDRAM_ARRAY_1_MODE_REGISTER_BASE)

#define MODE_REGISTER_STEP (ARRAY_1_MODE_REGISTER - ARRAY_0_MODE_REGISTER)

        // [6:4] /CAS Latency is 2 (2)
        // [ 3 ] Burst Type is 0, Sequential
        // [2:0] Burst Length is 2, meaning 4
#define SDRAM_MODE_REGISTER_SETUP 0x22
        // Shifted left 2 because this is a word-address-offset!
#define SDRAM_MODE_REGISTER_SETUP_OFFSET ((SDRAM_MODE_REGISTER_SETUP) << 2)

	
#define SDRAM_TIMING_VALUE        (SA110_SDRAM_ROW_PRECHARGE_2_CYCLES    | \
                                   SA110_SDRAM_LAST_DATA_IN_3_CYCLES     | \
                                   SA110_SDRAM_RAS_TO_CAS_DELAY_2_CYCLES | \
                                   SA110_SDRAM_CAS_LATENCY_2_CYCLES      | \
                                   SA110_SDRAM_ROW_CYCLE_TIME_4_CYCLES   | \
                                   SA110_SDRAM_COMMAND_DRIVE_SAME_CYCLE)

#define SDRAM_TIMING_VALUE_MIN    (SDRAM_TIMING_VALUE                    | \
                                   SA110_SDRAM_REFRESH_INTERVAL_MIN)

#define SDRAM_TIMING_VALUE_NORMAL (SDRAM_TIMING_VALUE                    | \
                                   SA110_SDRAM_REFRESH_INTERVAL_NORMAL)



	/*
	 * This subroutine sizes and configures up to four banks of SDRAM DIMMs.
	 * It runs early without a stack.
	 *
	 * R0 - R9 are destroyed. All others preserved.
	 * Except r11 which is also destroyed.
	 *
	 */
	.global __mem285_init
__mem285_init:

	/*
	 * First we find out whether the SDRAMs are already initialized,
	 * and if so, leave them alone.  RAM start implies just do the
	 * sizing sums to return top of memory.
	 */
	ldr	r0, =SA110_CONTROL_STATUS_BASE

#ifndef CYG_HAL_STARTUP_RAM
	// This is conditional even in ROM start for
	// a) testing ROM images eg. stubs in RAM really
	// b) cooperation with eg. POST code, so we are not really at reset
	ldr	r0, =SA110_CONTROL_STATUS_BASE
        ldr     r1, [r0, #SA110_SDRAM_TIMING_o]
	ldr	r2, =SDRAM_TIMING_VALUE_NORMAL
	cmps	r1, r2
	movne	r11, #0
	bne	12f
#endif	// ! defined CYG_HAL_STARTUP_RAM

	// Add up the sizes and return in r0:
	mov	r1, #SA110_SDRAM_ADDRESS_SIZE_ARRAY_0_o
	mov	r2, #0
	mov	r3, #1
    1:
	ldr	r4, [r0, r1]
	ands	r4, r4, #7		// if zero, no mem here
	addne	r2, r2, r3, asl r4	// tot up array sizes (in 1/2 Megs)
	add	r1, r1, #4
	cmps	r1, #(SA110_SDRAM_ADDRESS_SIZE_ARRAY_3_o + 4)
	blt	1b

	mov	r0, r2, asl #19		// get size into Mb
	mov	pc, lr

#ifndef CYG_HAL_STARTUP_RAM

    12:
	/*
         * Write to the SDRAM Timing Register in the 21285.  Disable
         * refresh totally.
         */
        mov     r1, #0
        str     r1, [r0, #SA110_SDRAM_TIMING_o]

	// Disable each array
	mov	r1, #0
        str     r1, [r0, #SA110_SDRAM_ADDRESS_SIZE_ARRAY_0_o]
        str     r1, [r0, #SA110_SDRAM_ADDRESS_SIZE_ARRAY_1_o]
        str     r1, [r0, #SA110_SDRAM_ADDRESS_SIZE_ARRAY_2_o]
        str     r1, [r0, #SA110_SDRAM_ADDRESS_SIZE_ARRAY_3_o]
	
        // Wait for 8 refresh cycles to complete
        mov     r1, #(9 * 32)
    1:  subs    r1, r1, #1
        bpl     1b

        /*
         * Force an all-banks recharge on all four SDRAM arrays
         *
         * This code came from the SA-IOP ver 1.0 (3-16-98) spec pg 22
         *
         * You must access all four arrays regardless of whether there is
         * memory there because the 21285 counts the precharge accesses and
         * inhibits access to the SDRAM until all four have been done.
         *
         * An all banks rechargs is initiated by a read from any address
         * in the mode register space.
         */

        mov     r1, #3 
        mov     r0, #ARRAY_0_MODE_REGISTER
   1:
        ldr     r2, [r0]
        add     r0, r0, #MODE_REGISTER_STEP
        subs    r1, r1, #1
        bpl     1b

        /*
         * Now we need to write to the SDRAM Mode Register.
         * The address is important, not the data.  The mode register
         * should be configured for a burst size of 4 with linear addressing
         */
        mov     r1, #3
        mov     r0, #ARRAY_0_MODE_REGISTER
   1:
        str     r0, [r0, #SDRAM_MODE_REGISTER_SETUP_OFFSET]
        add     r0, r0, #MODE_REGISTER_STEP
        subs    r1, r1, #1
        bpl     1b
        
        /*
         * Write to the SDRAM Timing Register in the 21285.  Set the
         * refresh interval to the minimum because we have to wait for
         * 8 refresh cycles to complete before we can rely on the SDRAMs
         * to be operating normally
         */
	ldr	r0, =SA110_CONTROL_STATUS_BASE
        ldr     r1, =SDRAM_TIMING_VALUE_MIN
        str     r1, [r0, #SA110_SDRAM_TIMING_o]

	// Disable each array
	mov	r1, #0
        str     r1, [r0, #SA110_SDRAM_ADDRESS_SIZE_ARRAY_0_o]
        str     r1, [r0, #SA110_SDRAM_ADDRESS_SIZE_ARRAY_1_o]
        str     r1, [r0, #SA110_SDRAM_ADDRESS_SIZE_ARRAY_2_o]
        str     r1, [r0, #SA110_SDRAM_ADDRESS_SIZE_ARRAY_3_o]
	
        // Wait for 8 refresh cycles to complete
        mov     r1, #(9 * 32)
    1:  subs    r1, r1, #1
        bpl     1b

        // Now reset the Refresh interval to a sensible value
        ldr     r1, =SDRAM_TIMING_VALUE_NORMAL
        str     r1, [r0, #SA110_SDRAM_TIMING_o]
	
	/* start out assuming 64M part with MUX mode 2 */
	mov	r1, #(SA110_SDRAM_SIZE_64MB | SA110_SDRAM_MUX_MODE2)
        str     r1, [r0, #SA110_SDRAM_ADDRESS_SIZE_ARRAY_0_o]
	add	r1, r1, #(64 << 20) // Add 64Mb
        str     r1, [r0, #SA110_SDRAM_ADDRESS_SIZE_ARRAY_1_o]
	add	r1, r1, #(64 << 20) // Add 64Mb again
        str     r1, [r0, #SA110_SDRAM_ADDRESS_SIZE_ARRAY_2_o]
	add	r1, r1, #(64 << 20) // Add 64Mb and again
        str     r1, [r0, #SA110_SDRAM_ADDRESS_SIZE_ARRAY_3_o]
	
	/*
	 * First, try to figure out which banks are populated and
	 * the real mux mode for those banks.
	 *
	 * At this point:
	 *   r0 - Base of control/status registers
	 *
	 * Register usage:
	 *   r8 - offset to SDRAM addr/size register
	 *   r5 - pattern
	 *   r4 - inverse pattern
	 *   r3 - scratch/mux mode output