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86 lines
1.8 KiB
ArmAsm
86 lines
1.8 KiB
ArmAsm
.text
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/* See https://www.codesourcery.com/archives/arm-gnu/msg01396.html
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and http://www.sourceware.org/ml/binutils/2005-04/msg00902.html
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This avoids unshifted register error which occurs when compiling for Thumb */
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.syntax unified
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.thumb
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.global main
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main:
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/* I have to use +1 in the address abel, otherwise the processor triggers
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an exception. The ARM documentation explains that thumb bx
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instructions require odd addresses. The C compiler does this
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automatically - I have examined the assembly generated by the C compiler,
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but still don't understand how they do it without manually appending
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a +1 to the address label. */
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.word 0x20000800 /* stack pointer */
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.word _c_entry+1 /* Entry point (reset vector) */
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.rept 82 /* interrupt handlers */
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.word _handler+1
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.endr
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_c_entry:
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/* Enable clock to Port C */
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movw r3, #4096
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movt r3, #16386
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ldr r2, [r3, #24]
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orr r2, r2, #16
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str r2, [r3, #24]
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/* Turn LED off */
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movw r3, #4096
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movt r3, #16385
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movw r2, #4096
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str r2, [r3, #16]
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ldr r2, [r3, #4] /* Change CRH pin 12 */
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and r2, r2, #4293984255
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orr r2, r2, #196608
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str r2, [r3, #4] /* MODE = general purpose I/O, speed 50 Mhz */
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ldr r2, [r3, #4] /* Get CRH */
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_flash_loop:
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/* Turn LED on */
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movw r2, #4096
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str r2, [r3, #20]
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movw r4, #0
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movt r4, #20
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delay1:
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sub.w r4, r4, #1
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cmp r4, #0
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bne delay1
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/* Turn LED off */
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movw r2, #4096
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str r2, [r3, #16]
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movw r4, #0
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movt r4, #3
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delay2:
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sub.w r4, r4, #1
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cmp r4, #0
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bne delay2
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B _flash_loop
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_handler:
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bx lr /* Return immediately */
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nop
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