EECE 631 Microcomputer System Design Lecture 6 Programming for Microcontrollers

1
EECE 631Microcomputer System DesignLecture 6
Programming for Microcontrollers

• Spring 2008
• Chris Lewis
• clewis_at_ksu.edu

2
Temperature Conversion Lab

• A2D
• A2D converter samples on a regular interval.
• ISR puts data into a specific memory location
• Data is only 10 bits, Other bits are garbage
• Convert A2D Counts to Temperature
• Celsius
• Fahrenheit
• Calibration
• Zero
• Boil

3
Integer Arithmetic

• Why use it?
• No FPU
• Faster more compact code
• What can go wrong?
• Overflow
• Truncation

4
Rounding

• // all vars ints
• D (AB)/C // truncates
• D (2A2BC)/(2C) // correct if pos
• D (2A2B-C)/(2C) // correct if neg

5
Working with Hardware

• Chip Mfgs give out code to aid in the use of
  their chips
• They are trying to minimize your development time
• Main problem, Configure, access hardware
• Cpu modules
• A2D and DAC
• PWM and Pulse Processing
• Timers, counters
• SPI, CAN, USB, etc

6
Pointer Method 1

• Three steps
• Define statement Name1 address
• define first 0x003fa00
• Type statement with Name2
• signed int data
• Set Name2 Name1
• data first //May give warning
• data (signed int ) first // No warning
• Now use Name2 to point to data
• result data // writes result to mem loc
  0x3fa00

7
Question

• Where is the number 0x3fa00 stored?
• // does not define a variable
• define my_new_var 10
• // It only tells the C-preprocessor to replace
• // every occurrence of the text
• // my_new_var with the text 10
• // BE VERY CAREFUL WITH defines

8
Pointer Method 2

• Method 2 One step
• Use type statement to define type, pointer and
  location
• signed int data (signed int ) (0x003fa000)
• Memory may also be altered without variables
• ((signed int )(0x003FA000))0xAAAA
• The next two slides demonstrate how this basic
  concept can result in somewhat bizarre code
• ADC QADC_A.RJURR0.R
• QADC_A.QACR1.B.MQ1 0x11

9
ifndef _MPC565_H_ define _MPC565_H_ /Device
specific defines/ define _UC3F_FLASH define
_MIOS14 define _MIOS14_RTC define
_CALRAM define _QADC64E / Out of RESET the
QADC64E runs in enhanced mode. If legacy mode is
needed/ / uncomment out the following
line./ /define QADC64E_LEGACY/ include
"m_usiu.h" /also includes UIMB
module/ include "m_flash.h" include
"m_tpu3.h" /also includes DPTRAM
module/ include "m_qadc64.h" include
"m_qsmcm.h" include "m_mios.h" include
"m_toucan.h" /also includes DLC module
/ include "m_sram.h" define USIU ((
struct USIU_tag ) (INTERNAL_MEMORY_BASE
0x2FC000)) define UC3F_A (( struct UC3F_tag
) (INTERNAL_MEMORY_BASE 0x2FC800)) define
UC3F_B (( struct UC3F_tag )
(INTERNAL_MEMORY_BASE 0x2FC840)) define TPU_A
(( struct TPU3_tag ) (INTERNAL_MEMORY_BASE
0x304000)) define TPU_B (( struct TPU3_tag
) (INTERNAL_MEMORY_BASE 0x304400)) define
TPU_C (( struct TPU3_tag )
(INTERNAL_MEMORY_BASE 0x305C00)) define QADC_A
(( struct QADC64_tag ) (INTERNAL_MEMORY_BASE
0x304800)) define QADC_B (( struct
QADC64_tag ) (INTERNAL_MEMORY_BASE
0x304C00)) define QSMCM_A (( struct QSMCM_tag
) (INTERNAL_MEMORY_BASE 0x305000)) define
QSMCM_B (( struct QSMCM_tag )
(INTERNAL_MEMORY_BASE 0x305400)) define MIOS14
(( struct MIOS_tag ) (INTERNAL_MEMORY_BASE
0x306000)) define CAN_A (( struct TOUCAN_tag
) (INTERNAL_MEMORY_BASE 0x307080)) define
CAN_B (( struct TOUCAN_tag )
(INTERNAL_MEMORY_BASE 0x307480)) define CAN_C
(( struct TOUCAN_tag ) (INTERNAL_MEMORY_BASE
0x307880)) define UIMB (( struct UIMB_tag
) (INTERNAL_MEMORY_BASE 0x307F80)) define
CALRAM_A (( struct CALRAM_tag )
(INTERNAL_MEMORY_BASE 0x380000)) define
CALRAM_B (( struct CALRAM_tag )
(INTERNAL_MEMORY_BASE 0x380040)) define
DPTRAM6K (( struct DPTRAM_tag )
(INTERNAL_MEMORY_BASE 0x300000)) define
DPTRAM4K (( struct DPTRAM_tag )
(INTERNAL_MEMORY_BASE 0x300040)) define DLCMD2
(( struct DLCMD2_tag ) (INTERNAL_MEMORY_BASE
0x300080)) endif / ifndef _MPC565_H /
10
union VUINT8 R struct
VUINT8 PQA71 VUINT8
PQA61 VUINT8 PQA51
VUINT8 PQA41 VUINT8 PQA31
VUINT8 PQA21 VUINT8 PQA11
VUINT8 PQA01 B
PORTQA union VUINT8 R
struct VUINT8 PQB71
VUINT8 PQB61 VUINT8 PQB51
VUINT8 PQB41 VUINT8 PQB31
VUINT8 PQB21 VUINT8
PQB11 VUINT8 PQB01 B
PORTQB

• struct QADC64_tag
• union
• VUINT16 R
• struct
• VUINT16 STOP1
• VUINT16 FRZ1
• VUINT166
• VUINT16 SUPV1
• VUINT16 MSTR1
• VUINT16 EXTCLK1
• VUINT161
• VUINT16 IARB4
• B
• QADC64MCR
• union
• VUINT16 R
• struct
• VUINT16 IRL15

11
ATMEL Technique

• Library functions
• __inline void AT91F_AIC_EnableIt (
• AT91PS_AIC pAic, // \arg pointer to the AIC
  registers
• unsigned int irq_id ) // \arg interrupt number
  to initialize
• // Enable the interrupt on the interrupt
  controller
• pAic-gtAIC_IECR 0x1 ltlt irq_id
• Structure Defs
• typedef struct _AT91S_AIC
• AT91_REG AIC_SMR32 // Source Mode
• AT91_REG AIC_IECR // Interrupt Enable
  Command
• AT91S_AIC, AT91PS_AIC

12
ATMELs Method Cont.

• Include file
• define AT91C_BASE_SYS ((AT91PS_SYS)
  0xFFFFF000) // (SYS) Base Address
• define AT91C_BASE_AIC ((AT91PS_AIC)
  0xFFFFF000) // (AIC) Base Address
• USAGE
• main()
• AT91PS_AIC pAic
• pAic AT91C_BASE_AIC

13
Embedded development sometimes requires
manipulating memory that has NOT been allocated

• int ptr_to_int (int )0x500
• This instruction allocates one 4 byte long region
  of memory pointing toward another memory location
  0x500
• What keeps the compiler from using 0x500 for
  other purposes?
• Choosing an arbitrary memory location is risky
• Choosing to point at the address of a peripheral
  modules control and data registers allows one to
  manipulate and read these registers.

14
Quirks of Compilers

• Sometimes, variables are deemed unnecessary, and
  removed to minimize the amount of code generated
  and the speed of execution.
• If lines of C code are significantly altered from
  original, it is hard to debug.
• TURN OPTIMIZATION OFF