"Butter bei de Fische" was: Re: [PATCH v3] score: PR1607: Add and use CPU_SIZEOF_POINTER

[Sebastian Huber]

On 11/09/2012 08:44 AM, Thomas Doerfler wrote:
> Sebastian, Ralf, can you both identify a typical piece of assembly code, that
> might be recoded into a more portable code? We could then consider, which versions
> - meet the portability requirements
> - meet the performance requirements
> - are readable and maintainable
> - interface properly to the C portion of the code

One interesting piece of assembler is this:

http://git.rtems.org/rtems/tree/cpukit/score/cpu/h8300/cpu_asm.S

[...]
SYM(_ISR_Handler):
#if defined(__H8300H__) || defined(__H8300S__) || defined(__H8300SX__)
	mov.l	er1, at -er7
	mov.l	er2, at -er7
	mov.l	er3, at -er7
	mov.l	er4, at -er7
	mov.l	er5, at -er7
	mov.l	er6, at -er7
	
/*  Set IRQ Stack */
	orc		#0xc0,ccr
	mov.l	er7,er6		; save stack pointer
	mov.l	@ISR_NEST_LEVEL,er1
	bne		nested
	mov.l	@INTERRUPT_STACK_HIGH,er7
	
nested:
	mov.l	er6, at -er7	; save sp so pop regardless of nest level
[...]

Firstly it uses:

#if defined(__H8300H__) || defined(__H8300S__) || defined(__H8300SX__)

which corresponds exactly to the part in my patch:

diff --git a/cpukit/score/cpu/h8300/rtems/score/cpu.h 
b/cpukit/score/cpu/h8300/rtems/score/cpu.h
index ea9d443..1811ce7 100644
--- a/cpukit/score/cpu/h8300/rtems/score/cpu.h
+++ b/cpukit/score/cpu/h8300/rtems/score/cpu.h
@@ -497,6 +497,12 @@ SCORE_EXTERN Context_Control_fp  _CPU_Null_fp_context;

  #define CPU_STACK_MINIMUM_SIZE          (1536)

+#if defined(__H8300H__) || defined(__H8300S__) || defined(__H8300SX__)
+  #define CPU_SIZEOF_POINTER 4
+#else
+  #define CPU_SIZEOF_POINTER 2
+#endif
+
  /*
   *  CPU's worst alignment requirement for data types on a byte boundary.  This
   *  alignment does not take into account the requirements for the stack.

Secondly it uses:

mov.l	@INTERRUPT_STACK_HIGH,er7

This is an indirect 32-bit load from address INTERRUPT_STACK_HIGH (part of 
_Per_CPU_Information).

I really like to see the trivial inline asm that can be used here.

-- 
Sebastian Huber, embedded brains GmbH

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