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ARM Initialization Question
- Date: Sun, 14 Sep 2008 01:16:12 +0800
- From: rayx.cn at gmail.com (ray)
- Subject: ARM Initialization Question
Gene Smith wrote:
> Sebastian Huber wrote:
>> I am quite new to the ARM architecture and try to develop a BSP for the
>> LPC2478. I have a question to the initialization code (random start.S):
You can try begin with rtl22xx BSP, which is base on lpc2210.
>> /* Set up the SVC stack pointer last and stay in SVC mode */
>> mov r0, #(PSR_MODE_SVC | PSR_I | PSR_F) /* No interrupts */
>> msr cpsr, r0
>> ldr r1, =_svc_stack_size
>> ldr sp, =_svc_stack
>> add sp, sp, r1
>> sub sp, sp, #0x64
>> Why is 0x64 subtracted from the stack pointer?
> I ran my app and skipped the subtract of 100 and it still worked OK.
> Seems like it is just wasting 100 bytes!
It is true that it is a wasting of 100 bytes. If you are running on
small sram cpu like lpc24xx, you can ignore this. But the 'wasting' 100
byte can help us separating stack from other segment of memory like a
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Thanks& Best Regards