The problem of formatting IAR sprintf floating point to 0.0 in UCOS assembly

Reference from http://blog.chinaunix.net/uid-21977330-id-3209252.html

1. Problem description :

When using uocs printf(),sprintf() Printing floating-point numbers will cause problems , But there will be no problem with bare metal

I use it now LPC1758 run UCOS, In the use of sprintf Print float When it's time , No matter what the value is, it will end up 0.0, But the type is int,short There is no problem with type . It is the task stack found on the Internet 8 Byte alignment is OK .

When there is no operating system , The system stack is 8 Byte Alignment , But when used ucos when , User tasks are not necessarily 8 Byte alignment .

Task 3  Stack start pointer in 0x1000000F4, No 8 Byte alignment , So, but in Task 3 Call... In the task printf Wait for a series of functions to have problems .

2. resolvent

I use it IAR, adopt #pragma data_alignment Specify the number of aligned bytes

#pragma data_alignment=8 // If not 8 Byte alignment ,sprintf Floating point numbers of will be output 0.0
static  OS_STK          App_TaskWorkModeCntStk[APP_CFG_TASK_WORKMODE_CNT_STK_SIZE];

OS_STK T_Stk[Task1_LED1_Stk_Size];

3. 8 Byte alignment reason

The history of this is ARM It does not support non aligned data access ; So there is 64Bit After the data operation instruction of , Directive requirements 8 Byte alignment . , in turn, , After a certain version of the compiler （RVCT3？）,AAPCS Just ask for stack 8 Byte alignment .

Yes, first 8 Byte Alignment AAPCS, And then there was CM3. Pay attention to the order .CM3 r2p0 Before , Automatic stack pressing is not required 8 alignment ,r2p0 It seems to be forced alignment .

printf Of 8 Alignment is C Required by the runtime , It's not about hardware ,C RTL The manual is written , You can read . Its roots lie in AAPCS requirement ; and AAPCS The root lies in LDRD Such instructions .

In other words, , In the future, if 128Bit Data operation has ,ARM It doesn't support non - , that AAPCS It may be upgraded to 16 Byte alignment .

For reference ,CM3 and C-RTL The question of alignment .

Thank you, blogger enzo26 Of ChinaUnix Blog