mem285.s

基于ecos的redboot

         *   r2 - scratch offset
         *   r1 - base address of 64M block in consideration
         *   r0 - base address of control register sets
	 */	
	mov	r8, #SA110_SDRAM_ADDRESS_SIZE_ARRAY_0_o
	mov     r1, #0

	ldr	r5, =0x12345678
	mvn	r4, r5

    20:
	str	r5, [r1]      // Offset 0 should work regardless
	str	r4, [r1, #4]  // put something else on the data bus
	ldr	r3, [r1]      // read back original
	cmps    r3, r5

	// If we didn't read pattern, then no memory present
	movne	r3, #0
	strne	r3, [r0, r8]            // write to addr/size register
	bne	49f                     // straight to next loop

	/*
	 * This bank is populated, so try to determine mux mode.
	 * All banks are currently set for mux mode 2.
	 */

	// A21 having no effect distinguishes the need for mux mode 0.
	str	r5, [r1]
	mov	r2, #(1 << 21)
	str	r4, [r1, r2]   // Store bad value at A21 mirror address
				 // expect to trash value at r1 if mode 0
	ldr	r3, [r1]
	cmps	r3, r5
	// If we don't read back pattern, then its mux mode 0
	
	// Force to 32M size to include A18 when sizing:
	movne	r3, #(SA110_SDRAM_SIZE_32MB | SA110_SDRAM_MUX_MODE0)
	bne	2f

	// A23 having effect distinguishes the need for mux mode 2.
	str	r5, [r1]
	mov	r2, #(1 << 23)
        str	r4, [r1, r2]   // Store bad value at A23 mirror address
                               // expect to preserve value at r1 if mode 2
	ldr	r3, [r1]
	cmps	r3, r5
	// if pattern still there, then mode 2
	moveq	r3, #(SA110_SDRAM_SIZE_64MB | SA110_SDRAM_MUX_MODE2)
	beq	2f

	// A22 having effect distinguishes the need for mux mode 4.
	str	r5, [r1]
	mov	r2, #(1 << 22)
	str	r4, [r1, r2]   // Store bad value at A22 mirror address
                               // expect to preserve value at r1 if mode 4
	ldr	r3, [r1]
	cmps	r3, r5
	// if pattern A still there, then mode 4
	moveq	r3, #(SA110_SDRAM_SIZE_64MB | SA110_SDRAM_MUX_MODE4)
	beq	2f

	/*
	 * At this point it is either mode 1 or 3. There is no clear cut
	 * test to differentiate the two, so make a best guess now, then
	 * correct later (if necessary) while sizing the bank.
	 */

        // NB the bank is still in mux mode 2, so A24 is fed to the wire for
        // A22 (mode 1) or no-connection (mode 3); so:
        // A24 having effect distinguishes the need for mux mode 1
        // A24 having no effect distinguishes the need for mux mode 3
	str	r5, [r1]
	mov	r2, #(1 << 24)
	str	r4, [r1, r2]
	ldr	r3, [r1]
	cmps	r3, r5
	// If pattern, try mode 1
	moveq	r3, #(SA110_SDRAM_SIZE_64MB | SA110_SDRAM_MUX_MODE1)
        // otherwise, try mode 3
	movne	r3, #(SA110_SDRAM_SIZE_64MB | SA110_SDRAM_MUX_MODE3)

	bne 2f

    2:
	orr	r3, r3, r1			// add in base address
	str	r3, [r0, r8]			// write to addr/size register
        
	/*
	 * Now that mux mode for this array is (hopefully) setup, we can try
	 * to size this SDRAM array.
         * 
         * Register usage:
         *    r8 - offset to current size/mode register
         *    r1 - offset to current base (in 64M blocks)
         *    r0 - base address of control register sets
	 */

        mov     r4, #(63 << 20)         // 63Mb to start with
    1:  str     r4, [r1, r4]
        subs    r4, r4, #(1 << 20)      // go down in increments of 1Mb
        bpl     1b

	str	r4, [r1, #4]            // change pattern on data bus

	// search for first unexpected data in ascending order
        mov     r4, #0
    1:
	ldr	r5, [r1, r4]
        cmps    r5, r4
	bne	23f                     // different so end of array
        add     r4, r4, #(1 << 20)      // go up in increments of 1Mb
        cmps    r4, #(64 << 20)
	blt	1b
        // fall-through assumes it is a 64Mb device
   23:	
	movs	r4, r4, lsr #20		// get a plain number of Mb
	// if this gave a zero, maybe we were mistaken about the RAM
        // working earlier: disable this bank.
	streq	r4, [r0, r8]            // write to addr/size register
	beq	49f                     // straight to next loop

        // apparently, mode 3 devices *must* be 8Mb; if we got a different
        // answer, set it to mode 1 and go back to try again:
	cmps    r4, #8
        beq     4f

	// skip if 8Mb; we are happy
	ldr     r3, [r0, r8]  	        // read in the mode we set
	and	r3, r3, #SA110_SDRAM_MUX_MODE_MASK
	cmp	r3, #SA110_SDRAM_MUX_MODE3
	// Must be misconfigured mux mode. Set to mode 1 and retry
	moveq	r3, #(SA110_SDRAM_SIZE_64MB | SA110_SDRAM_MUX_MODE1)
	beq     2b
	// not mux mode 3; drop though OK

    4:
	// convert MB size to register size val
	mov	r5, #0
	mov     r3, r4
    5:  movs    r3, r3, lsr #1
        add	r5, r5, #1
        bcc     5b

	// Double check that the size was a power of 2
	mov     r6, #1
        mov     r6, r6, lsl r5		// should get Mb count back doubled
	cmps	r6, r4, lsl #1          // compare with doubled
	movne	r5, #0			// disable this bank
        ldr	r3, [r0, r8]            // Load current setting
	bic     r3, r3, #7
	orr	r3, r3, r5		// insert the correct size code
	str	r3, [r0, r8]		// into the control register

   49:
	add	r8, r8, #4			// next addr/size register
	add	r1, r1, #(64<<20)		// next array
        cmps    r1, #(256<<20)                  // top address + 1 bank
	blt	20b
        // END of main loop to size all 4 DRAM banks

	/*
	 * At this point, the size values are all in the control registers.
	 *
	 * We want to set memory up to be contiguous. Since the
	 * banks' base address needs to be naturally aligned, we
	 * need to sort the bank sizes from large to small.
	 *
	 * Register usage:
         *   r0 - base address of control register sets
	 *   r1	- bitmap of which slots we have covered in toto
	 *   r2	- cumulative base address of mapped SDRAM
	 *   r3	- biggest size code this pass
	 *   r4	- bit index of current slot
	 *   r5	- bit index of biggest slot found this pass
	 *   r6	- scratch control reg contents
	 *   r7 - scratch size code
	 *   r8 - address of current slot's control register
	 *   r9	- address of biggest slot found's control register
	 */
	mov	r1, #0			// bitmap of which we have covered
	mov	r2, #0			// cumulative base address
	// do... until there are no more slots to deal with
    70:
	mov	r3, #0			// biggest this pass
	mov     r4, #1			// bit index of current slot
	mov	r5, #0			// bit index of biggest slot found
	mov	r8, #SA110_SDRAM_ADDRESS_SIZE_ARRAY_0_o
	mov	r9, #0			// address of biggest slot found
	// Foreach slot we have not yet dealt with
    75:
	tst	r4, r1
	bne	88f
	ldr	r6, [r0, r8]
	and	r7, r6, #7
	cmps	r7, r3
	movgt	r3, r7			// save biggest's size
	movgt	r5, r4			// save biggest's index
	movgt	r9, r8			// save biggest's reg address
    88:
	mov	r4, r4, asl #1
	add	r8, r8, #4
	cmps	r4, #0x10
	blt	75b			// next slot
	// Did we find a largest slot?
	cmps	r5, #0
	beq	95f	// No!  Finished

	orr	r1, r1, r5		// can forget r4 and r5 now
	ldr	r6, [r0, r9]		// get the control register
	bic	r6, r6, #0x0ff00000	// clear base address bits
	orr	r6, r6, r2		// insert base address to use
	str	r6, [r0, r9]		// store the new control register
	mov	r6, #1
	mov	r6, r6, asl r3
	mov	r6, r6, asl #19		// 1 << (size-code + 19) is size
	add	r2, r2, r6		// increment the cumulating address

	b	70b			// go look for the next one

    95:	// all done!
	// at this point, r2 contains the top of memory.
	// (r11 is the value from last time or zero if first time)

	cmps	r11, r2			// Same answer as last time?
	movne	r11, r2			// if not, save memsize
	bne	12b			// ...and try again.
	
	mov	r0, r2
	mov	pc, lr	
#endif // ! defined CYG_HAL_STARTUP_RAM
//FUNC_END __mem285_init

/* EOF mem285.S */