Optimization: Use a trampoline to start ARM processes instead of wasting one stack...

[bertos.git] / bertos / cpu / arm / hw / switch_ctx_arm.S

diff --git a/bertos/cpu/arm/hw/switch_ctx_arm.S b/bertos/cpu/arm/hw/switch_ctx_arm.S
index 39e9f46a2dabb58b88475203acf095dacd9a1155..e610ac97c535073bb3cbbcc798299c792aaced57 100644 (file)
--- a/bertos/cpu/arm/hw/switch_ctx_arm.S
+++ b/bertos/cpu/arm/hw/switch_ctx_arm.S
@@ -43,12 +43,6 @@
 asm_switch_context:
        mrs     r2, cpsr               /* Save status. */
 
-       /*
-        * To work correctly the lr should point to proc_exit, so when process finish
-        * could be return
-        */
-       push {lr}                  /* Add one element on stack, for next switching */
-
        stmfd   sp!, {r2, r4-r11, lr}  /* Save registers. */
 
        str     sp, [r1]               /* Save old stack pointer. */
@@ -57,5 +51,15 @@ asm_switch_context:
        ldmfd   sp!, {r2, r4-r11, lr}  /* Load new registers. */
        msr     cpsr, r2               /* restore flags reg. */
 
-       pop {r0}                  /* pop on stack address of the process that we want to jump */
-       mov     pc, r0
+       mov     pc, lr
+
+
+/* proc_entry trampoline needed because ARM does not pop return addresses
+from the stack, but uses lr instead.*/
+.globl asm_proc_entry
+asm_proc_entry:
+       mov     lr, pc
+       /* In r11 we have the real process entry point as set up by CPU_CREATE_NEW_STACK */
+       bx      r11
+       bl      proc_exit
+