" ssbx intm" or "xc 1,unc" + "ssbx intm"? | TMS320C54x

Technical discussions about the TI C54x DSPs (including the c5401, c5402, c5402a, c5404, c5407, c5409, c5409a, c5410, c5410a, c5416, c5420, c5421, c5441, c549, c5470 and c5471).

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Dear all, Should we use the "xc 1,unc" + "ssbx intm" instead of mere "ssbx intm" to avoid a potential pipeline bug? For those of you who happened to have read the SPRA640. If you also read the SPRA640A, you will notice that the author deletes the following paragraphs in chapter 3.4: "Wrong. If an interrupt occurs after line 1 is fetched, but before it is executed, a problem occurs. The CPU will automatically globally disable interrupts via the INTM bit, and line 1, when it executes, will have no effect. It will execute, since it had been fetched before the interrupt occurred. When the ISR completes, it will clear INTM, thus enabling interrupts. Processing will continue in our example at line 2, but interrupts will be enabled! So, the original problem may occur again. This will be another headache to debug, since the example code clearly disables interrupts. So, we need a way to protect the disabling instruction from interruption. The solution is as follows: 1 XC 1,UNC 2 SSBX INTM 3 STLM A,AR2 4 STLM B,AR2 5 NOP 6 LD *AR2,A 7 LD *AR2,B 8 RSBX INTM Example 2B The XC instruction on the C54x protects the next 1-word instruction from interruption, e.g., it ensures that the instruction will execute unconditionally." I read the pipeline chapters of TI's CPU reference UG carefully. It seems to me that the "ssbx intm" actually won't have a pipeline problem as described in SPRA640. That might be the reason why the paragraphs above are deleted. Am I right or I missed something? I attached the SPRA640 for reference. The SPRA640A could be found at http://focus.ti.com/docs/apps/catalog/resources/appnoteabstract.jhtml?ab stractName=spra640a. Any reply will be appreciated. Jane Tri-Link Technologies Inc. #301-8988, Fraserton Court Burnaby, BC V5J 5H8 Tel: (604) 451-9113 Fax: (604) 451-9118 Email:

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" ssbx intm" or "xc 1,unc" + "ssbx intm"? - Jane Shen - Feb 26 18:52:00 2002