We should document our code. You can find a flowchart tool in
Word or Powerpoint.
This could be useful for lab reports. int fac_c(int x) x < = 0 f = 0 f = 1 x > 1 f = f * x x = x-1 End return f if else N Y Y N while int fac_c(int x) { int f; if(x <= 0) f = 0; else { f = 1; while(x > 1) { f = f * x; x--; } } return f; } fac_c(5)
calculates
1*5*4*3*2*1=120 Flowchart
main in C
#include extern int fac_asm(int); int fac_c(int); int main(void) { int c_result, asm_result; int x; while(1) { printf(”Enter a number: ”); scanf(”%d”, &x); c_result = fac_c(x); asm_result = fac_asm(x); printf(”C-result: %d\n”, c_result); printf(”Asm-result: %d\n”,asm_result); } return 0; } Message to the linker: fac_asm() is an external function (from an other file).
Structure diagram?
To document the program structure, a structure diagram could be useful. It could be directly translated into structured programming. ( while, if, else … ) But in assembler, we are not interested in the program structure, but in the program flow.
The Flowchart
The flowchart could be directly translated to assembler code.
How to program the Nios processor?
The Nios processor is the Altera version of a MIPS processor.
It is designed to make efficient use of the resources in a FPGA.
It comes in three versions: Small – Medium – Large …
Nios II registers 0…15
Use as constant ”0”! If you call a subroutine, save the contents of the registers you’ve used on stack!
Pseudoinstruction:
ble branch if less than or equal signed
bge is the ble with register A and B swapped! The IMM16 adress is effectively a 18 Byte-adress because instructions must be word-aligned.
Conditional operators of C
All C-language conditional operators have assembly instructions (or pseudoinstructions). Compare two registers and branch relative if the expression is true.
Memory content, Load and Store
Store in memory …
stw r6, 100(rA)
The call and ret instructions
From Flowchart to assembler
Assembler
.global fac_asm .text # Parameter in r4 (and if needed in r5, r6, r7) # Return value in r2 (and r3 if long or double) # we can use r2 and r3 for calculations until return # r8 … r15 must be saved by caller of a sub fac_asm: # int r2 fac_asm(int r4 x), the function prototype # r3 : for constant ”1” if: ble r4, r0, else # if(x <= 0) movi r3, 1 # constant ”1” mov r2,r3 # f = 1 while: ble r4,r3, endsub # while(x>1){ mul r2,r2,r4 # f = f*x sub r4,r4,r3 # x = x - 1 br while # } else: mov r2, r0 # f = 0 endsub: ret # return r2 .end fac_asm has to be made known to other files
Exercises Embedded Systems
2.1 Prioritized interrupts
Exercises Embedded Systems
2.2 Input/Output
R/W reverses the direction of the databuss.
CS Chip Select enables the chip Connect a 8 register memory-mapped peripheral to the CPU. The CPU has 8 bit address and data busses.
The peripheral should have registeraddresses 0x10…0x17.
Comments