switch_dsp56k.c

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00001 
00037 void asm_switch_context(void ** new_sp /* R2 */, void ** save_sp /* R3 */);
00038 asm void asm_switch_context(void ** new_sp, void ** save_sp)
00039 {
00040     lea   (SP)+
00041 
00042     ; From the manual:
00043     ; The compiler uses page 0 address locations X: 0x0030 - 0x003F as register
00044     ; variables. Frequently accessed local variables are assigned to the page 0
00045     ; registers instead of to stack locations so that load and store instructions
00046     ; are shortened. Addresses X: 0x0030 - 0x0037 (page 0 registers MR0-MR7) are
00047     ; volatile registers and can be overwritten. The remaining registers (page 0
00048     ; registers MR8-MR15) are treated as non-volatile and, if used by a routine,
00049     ; must be saved on entry and restored on exit.
00050     ;
00051     ; So, register 0x30-0x37 are caller-save, while 0x38-0x3F are callee-save.
00052     move  x:<$38,y1
00053     move  y1,x:(SP)+
00054     move  x:<$39,y1
00055     move  y1,x:(SP)+
00056     move  x:<$3A,y1
00057     move  y1,x:(SP)+
00058     move  x:<$3B,y1
00059     move  y1,x:(SP)+
00060     move  x:<$3C,y1
00061     move  y1,x:(SP)+
00062     move  x:<$3D,y1
00063     move  y1,x:(SP)+
00064     move  x:<$3E,y1
00065     move  y1,x:(SP)+
00066     move  x:<$3F,y1
00067     move  y1,x:(SP)
00068 
00069     ;
00070     ; Switch stacks
00071     nop
00072     move SP, x:(R3)
00073     nop
00074     move x:(R2), SP
00075     nop
00076 
00077     ;
00078     ; restore all saved registers
00079     ;
00080     pop   y1
00081     move  y1,x:<$3F
00082     pop   y1
00083     move  y1,x:<$3E
00084     pop   y1
00085     move  y1,x:<$3D
00086     pop   y1
00087     move  y1,x:<$3C
00088     pop   y1
00089     move  y1,x:<$3B
00090     pop   y1
00091     move  y1,x:<$3A
00092     pop   y1
00093     move  y1,x:<$39
00094     pop   y1
00095     move  y1,x:<$38
00096 
00097     ; SR is already pushed on the stack (normal call context). Use RTI to restore
00098     ; it, so that interrupt status is preserved across the tasks.
00099     rti
00100 }