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Porting FreeRTOS to v850 Fx4

Posted by huzhiping on December 13, 2013

I am trying to port FreeRTOS to v850 Fx4 based on Fx3, but using GreenHills compiler. Sereval issues found: 1. From FreeRTOS offical website, it is said "6.If the stack on the microcontroller being ported to grows downward from high memory to low memory then set portSTACKGROWTH in portmacro.h to -1, otherwise set portSTACKGROWTH to 0." --> in here, http://www.freertos.org/FreeRTOS-porting-guide.html..., if you set "portSTACKGROWTH to 0", then you got a compiler error, "pxEndOfStack" is undefined, you have to set "portSTACKGROWTH to be greater than 0", which in Tasks.c, the condition is "portSTACK_GROWTH > 0".

  1. I created 2 simple tasks with function by setting a different LED ON in each task, When I using debugger, 2 tasks (priority is different, task 2 is 2, task1 is 1) and the idle task all created successfully, but in function "xPortStartScheduler()-->vPortStart() -> portRESTORECONTEXT (assembly macro), it can NOT get the right address of "pxCurrentTCB" that is for task2. my vPortStart() function is:

vPortStart: portRESTORECONTEXT -- Restore the context of whichever task the ... ld.w 0[sp],lp ldsr lp,5 -- restore PSW DI ld.w 4[sp],lp -- restore LP ld.w 8[sp],lp -- restore LP ADD 0x0C,sp -- set SP to right position EI jmp [lp]

  1. I tried different heapx.c, I found each time after call vPortStat()->portRESTORECONTEXT the stack pointer of "pxCurrentTCB" is different. I double checked the "portRESTORECONTEXT" and "portSAVE_CONTEXT", it looks like correct. I attched these assembly macro below:

.macro portSAVECONTEXT prepare {r20,r21,r22,r23,r24,r26,r27,r28,r29,r30},18,sp -- save general purpose registers sst.w r19,68[ep] sst.w r18,64[ep] sst.w r17,60[ep] sst.w r16,56[ep] sst.w r15,52[ep] sst.w r14,48[ep] sst.w r13,44[ep] sst.w r12,40[ep] sst.w r11,36[ep] sst.w r10,32[ep] sst.w r9,28[ep] sst.w r8,24[ep] sst.w r7,20[ep] sst.w r6,16[ep] sst.w r5,12[ep] sst.w r2,8[ep] sst.w r1,4[ep] MOVHI hi(usCriticalNesting),r0,r1 -- save usCriticalNesting value to stack ld.w lo(usCriticalNesting)[r1],r2 sst.w r2,0[ep] MOVHI hi(pxCurrentTCB),r0,r1 -- save SP to top of current TCB ld.w lo(_pxCurrentTCB)[r1],r2 st.w sp,0[r2] .endm

.macro portRESTORECONTEXT MOVHI hi(pxCurrentTCB),r0,r1 -- get Stackpointer address ld.w lo(pxCurrentTCB)[r1],sp MOV sp,r1 ld.w 0[r1],sp -- load stackpointer MOV sp,ep -- set stack pointer to element pointer sld.w 0[ep],r1 -- load usCriticalNesting value from stack MOVHI hi(usCriticalNesting),r0,r2 st.w r1,lo(_usCriticalNesting)[r2] sld.w 4[ep],r1 -- restore general purpose registers sld.w 8[ep],r2 sld.w 12[ep],r5 sld.w 16[ep],r6 sld.w 20[ep],r7 sld.w 24[ep],r8 sld.w 28[ep],r9 sld.w 32[ep],r10 sld.w 36[ep],r11 sld.w 40[ep],r12 sld.w 44[ep],r13 sld.w 48[ep],r14 sld.w 52[ep],r15 sld.w 56[ep],r16 sld.w 60[ep],r17 sld.w 64[ep],r18 sld.w 68[ep],r19 dispose 18,{r20,r21,r22,r23,r24,r26,r27,r28,r29,r30} .endm

I don't know how to do it next, hopefully I can get help from you.

Thanks in advance!

Albert


Porting FreeRTOS to v850 Fx4

Posted by rtel on December 14, 2013

There is already a V850ES port for IAR. You can use that as a base, and basically just copy it but using the GreenHills compiler. I'm afraid I don't have GreenHills tools so don't know anything about them.

portSTACKGROWTH in portmacro.h to -1, otherwise set portSTACKGROWTH to 0

That was incorrect, portSTACK_GROWTH should be -1 or 1, not 0. I have updated the documentation. In your case I think it should be -1 anyway but would have to check.

Regards.


Porting FreeRTOS to v850 Fx4

Posted by huzhiping on December 16, 2013

Question about the function of _vPortStart below:

vPortStart: portRESTORECONTEXT -- Restore the context of whichever task the ... ld.w 0[sp],lp ldsr lp,5 -- restore PSW DI ld.w 4[sp],lp -- restore LP ld.w 8[sp],lp -- restore LP ADD 0x0C,sp -- set SP to right position EI jmp [lp]

In this function, the first line is "portRESTORECONTEXT" to get the "pxCurrentTCB" task context. But after you create all the tasks, the highest priority task is the "pxCurrentTCB" and all the tasks never use "portSaveCONTEXT" to save all the r0~r30 registers, if you use "portRESTORE_CONTEXT", it will get the wrong context registers value.

In my case, I have task1 and task2, and task2 has the highest priority, after they are created, pxCurrentTCB is task2, but after call "vPortStart" and "portRESTORE_CONTEXT", it got the different register values, so it never call task2 to run.

Is this correct? and how do I fix it?

Thanks for you help!

Albert


Porting FreeRTOS to v850 Fx4

Posted by rtel on December 16, 2013

Gosh, its a long time since I've looked at that port, but i'm not sure if I follow your post.

As you say, the first thing vPortStart() calls is portRESTORECONTEXT(), and the first thing portRESTORECONTEXT() does is load the stack pointer from the pxCurrentTCB variable. Therefore the first task to execute will be that pointed to by pxCurrentTCB.

portRESTORECONTEXT() then pops that task's context from its stack, which was pre-loaded with values by the pxPortInitialiseStack() function, which was called (internally by the RTOS) when the task was created. After portRESTORECONTEXT() is called vPortStart() obtains the address of the tasks entry point from the tasks stack, and jumps to it to kick the task off.

Which bit am I missing?

Regards.


Porting FreeRTOS to v850 Fx4

Posted by huzhiping on December 16, 2013

Yes. Right. My question is that after you created all the tasks, the highest priority task is the pxCurrentTCB task, when you create these tasks, the highest priority may not the last task to be created, and we didn't use portSAVECONTEXT, Although we can get the right pxCurrentTCB stack address, but rest of the rigsters in r0~31 may have different values, therefore, when you call portRESTORECONTEXT of vPORTSTART, it will not get the right task context, I am right?

My portRESTORE/SAVE_CONTEXT functions are in my first post.

Thanks.

Albert


Porting FreeRTOS to v850 Fx4

Posted by edwards3 on December 16, 2013

When the scheduler is started pxCurrentTCB will already be pointing to the highest priority task that was created before that point.


Porting FreeRTOS to v850 Fx4

Posted by richard_damon on December 17, 2013

When tasks are created, they are created "As if" a portSAVE_CONTEXT was called, this is a requirement of the routine that sets up the initial stack of a task.


Porting FreeRTOS to v850 Fx4

Posted by huzhiping on December 19, 2013

Thanks for the help!

Albert


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