On 10/06/2010 12:35 PM, Daniel Walker wrote:
> Is it possible to do all this in assembly ? Can't you have the default
> implementation using this assembly with different function names, then
> just set the assembly function names in C code someplace?
Sure we could do that. I went this route because adding the timer based
delay code was a copy paste instead of a copy translate. Actually, after
adding the set_delay_fn code __const_udelay and __delay aren't inlined
into __udelay anymore so we're back to the noinline behavior except
we're missing interleaving.
Finally, I thought it would be clearer what was going on if it was in C
as opposed to assembly. How bad is a branch as opposed to fall through.
And more importantly, how bad is a push/pop?
00000000 <delay_loop>:
0: e2500001 subs r0, r0, #1 ; 0x1
4: 8afffffd bhi 0 <delay_loop>
8: e12fff1e bx lr
0000000c <set_delay_fn>:
c: e59f3004 ldr r3, [pc, #4] ; 18 <set_delay_fn+0xc>
10: e5830000 str r0, [r3]
14: e12fff1e bx lr
18: 00000000 .word 0x00000000
0000001c <__delay>:
1c: e92d4010 push {r4, lr}
20: e59f3008 ldr r3, [pc, #8] ; 30 <__delay+0x14>
24: e1a0e00f mov lr, pc
28: e593f000 ldr pc, [r3]
2c: e8bd8010 pop {r4, pc}
30: 00000000 .word 0x00000000
00000034 <__const_udelay>:
34: e59f3018 ldr r3, [pc, #24] ; 54 <__const_udelay+0x20>
38: e1a00720 lsr r0, r0, #14
3c: e5933000 ldr r3, [r3]
40: e1a03523 lsr r3, r3, #10
44: e0000093 mul r0, r3, r0
48: e1b00320 lsrs r0, r0, #6
4c: 012fff1e bxeq lr
50: eafffffe b 1c <__delay>
54: 00000000 .word 0x00000000
00000058 <__udelay>:
58: e59f3004 ldr r3, [pc, #4] ; 64 <__udelay+0xc>
5c: e0000093 mul r0, r3, r0
60: eafffffe b 34 <__const_udelay>
64: 0001a36e .word 0x0001a36e
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