ASM Example Program and C Equivalent

Comparison between Assembly Code and C Code

Multi-byte math in C is a breeze compared to ASM:

C:	x32 = x32 + 1234;
ASM:	movlw 0xd2 addwf x32,f movlw 04 btfsc 03.0 movlw 05 addwf x32+1,f movlw 00 btfsc 03.0 movlw 01 addwf x32+2,f movlw 00 btfsc 03.0 movlw 01 addwf x32+3,f

C data structures can be much more easily expressed in C for example:

C:	device_list[3].flags.active_flag = 1;
ASM:	bsf device_list+DL_ENTRY_SIZE*3+DL_FLAG_OFFSET, ACTIVE_FLAG

In assembly bank switching (RAM banks) and program memory paging must always be considered:

C:	MyVar = 12;
ASM:	movlw 0x0C bcf status,bs7 ; Set to RAM bank 2 bsf status,bs8 movwf MyVar

Here is an example ASM function and the C equivalent:

void parse_userid(char var_2) {
	char loop_count;
	char send_reg;

	for(loop_count=6;loop_count>0;loop_count--) {
		send_reg=BufferRead();
		shift_right(&send_reg,1,0);
		if(send_reg!=' ')
			do_serial_send(send_reg);
		offset++;
	}
	UID_buffer=BufferRead();
	shift_right(&UID_buffer,1,0);
	UID_buffer&=0x0F;
	if(UID_buffer!=0) {
		do_serial_send('0');
		if(UID_buffer>=10) {
			UID_buffer-=10;
			do_serial_send('1');
		}
		do_serial_send(UID_buffer+0x30);
	}
	if((offset^var_2)==0)
		do_serial_send('*');
}

ASM:


					
						parse_userid:
					
					
						movlw
						0x06
						
					
					
						movwf
						loop_count
						;6 loops
					
					
						parse_userid_loop:
					
					
						call
						BufferRead
						;get byte from RAM
					
					
						movwf
						send_reg
						;byte to send_reg
					
					
						bcf
						status,carry
						
					
					
						rrf
						send_reg,F
						;right shift to normal
					
					
						movfw
						send_reg
						
					
					
						xorlw
						' '
						;space ?
					
					
						btfss
						status,zero
						;yes, skip next
					
					
						call
						do_serial_send
						;no, send byte
					
					
						incf
						offset,F
						;inc offset
					
					
						decfsz
						loop_count,F
						;loop count - 1
					
					
						goto
						parse_userid_loop
						
					
					
						;
						
						
					
					
						call
						BufferRead
						;get stored UID byte
					
					
						movwf
						UID_buffer
						
					
					
						rrf
						UID_buffer,F
						;right shift byte
					
					
						movlw
						0x0f
						
					
					
						andwf
						UID_buffer,F
						;mask hi nibble
					
					
						btfsc
						status,zero
						;yes, skip next
					
					
						goto
						UID_is_zero
						;UID = 0
					
					
						movlw
						'-'
						;add dash
					
					
						movwf
						send_reg
						
					
					
						call
						do_serial_send
						;send -
					
					
						movlw
						d'10'
						;10
					
					
						subwf
						UID_buffer,W
						;test magnitude
					
					
						btfss
						status,carry
						;yes, skip next
					
					
						goto
						send_the_ones
						;UID < 10
					
					
						movwf
						UID_buffer
						;UID buffer => 10
					
					
						movlw
						"1"
						;ascii 1 for tens
					
					
						movwf
						send_reg
						;W to send_reg
					
					
						call
						do_serial_send
						;send 10
					
					
						send_the_ones:
					
					
						movfw
						UID_buffer
						;UID to W
					
					
						addlw
						0x30
						;ascii convert
					
					
						movwf
						send_reg
						
					
					
						call
						do_serial_send
						
					
					
						UID_is_zero:
						;do asteric routine
					
					
						movfw
						var_2
						
					
					
						xorwf
						offset,W
						;check for loc match to
					
					
						bnz
						$+4
						;sending digi
					
					
						movlw
						"*"
						
					
					
						movwf
						send_reg
						
					
					
						call
						do_serial_send
						;send * to denote
					
					
						return