NU32v2: Digital I/O Assembly Code - Revision history

Lynch at 11:22, 16 January 2016

2016-01-16T11:22:29Z

Lynch at 12:09, 26 January 2011

2011-01-26T12:09:17Z

Lynch at 12:09, 26 January 2011

2011-01-26T12:09:03Z

Lynch at 12:08, 26 January 2011

2011-01-26T12:08:03Z

Lynch at 09:28, 26 January 2011

2011-01-26T09:28:35Z

Lynch at 09:28, 26 January 2011

2011-01-26T09:28:00Z

Lynch at 09:25, 26 January 2011

2011-01-26T09:25:02Z

Lynch at 16:43, 25 January 2011

2011-01-25T16:43:18Z

Lynch at 16:43, 25 January 2011

2011-01-25T16:43:01Z

Lynch at 16:42, 25 January 2011

2011-01-25T16:42:45Z

← Older revision		Revision as of 11:22, 16 January 2016
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			'''THIS PAGE REFERS TO A PRE-RELEASE VERSION OF THE NU32 PIC32 DEVELOPMENT BOARD. FOR INFORMATION, SAMPLE CODE, AND VIDEOS RELATED TO THE PRODUCTION VERSION (2016 AND LATER), AND TO THE CORRESPONDING BOOK "EMBEDDED COMPUTING AND MECHATRONICS WITH THE PIC32 MICROCONTROLLER," VISIT [[NU32\|THE NU32 PAGE]].'''

	Let's say we called our source code digio.c. When we compile it, we find an "object code" file digio.o somewhere. I can "disassemble" this object code to see an assembly language version of the code. (You can either do this directly in the MPLAB IDE, or run the command-line functions pic32-nm or pic32-objdump with your .o file as the argument. These can be found in your C32 directory under "bin." For example, to produce the output below, I used <tt>pic32-objdump -D digio.o</tt>.) When we look at our disassembled code, we see a lot of stuff, including the block of code below. I added the comments beginning with //, since we don't know assembly language.		Let's say we called our source code digio.c. When we compile it, we find an "object code" file digio.o somewhere. I can "disassemble" this object code to see an assembly language version of the code. (You can either do this directly in the MPLAB IDE, or run the command-line functions pic32-nm or pic32-objdump with your .o file as the argument. These can be found in your C32 directory under "bin." For example, to produce the output below, I used <tt>pic32-objdump -D digio.o</tt>.) When we look at our disassembled code, we see a lot of stuff, including the block of code below. I added the comments beginning with //, since we don't know assembly language.

@@ Line 23: / Line 23: @@
 I see 11 instructions in the loop, just less than my estimated 12 instructions.
-<1-- Usually we have one assembly instruction per machine instruction (cycle), but sometimes an assembly instruction expands to more than one machine instruction.  Is that what's happening here---there's an extra machine instruction we're not seeing?  Or bad timing by me?  Not sure. -->
+<!-- Usually we have one assembly instruction per machine instruction (cycle), but sometimes an assembly instruction expands to more than one machine instruction.  Is that what's happening here---there's an extra machine instruction we're not seeing?  Or bad timing by me?  Not sure. -->
 Notice our use of the constant 10,000,000 in the code actually requires two assembly instructions to load the value into register v0:  one for the most significant half-word (16 bits), and one for the least significant half-word.  We have a limit of 32 bits total to specify the instruction (and some of them are used for the opcode and specifying the register).  If we created a variable and assigned it the value 10,000,000, on the other hand, the entire word could be loaded with one lw instruction.

@@ Line 22: / Line 22: @@
 The first number in each row is the address of the instruction relative to the start of the program at 000.  (Note that the instructions are each 4 bytes long, or 32 bits, so the address of each successive instruction is 4 bytes greater than the previous one.)  The second number is the 32-bit instruction written in hexadecimal; the first several bits are for the instruction type, or "opcode," and the remaining bits are to specify registers, memory locations, values, etc., used by the instruction.  The next column is the opcode in human-readable form, and the last column contains the human-readable form of the registers, memory locations, values, etc., used by the instruction.
-I see 11 instructions in the loop, just less than my estimated 12 instructions.  Usually we have one assembly instruction per machine instruction (cycle), but sometimes an assembly instruction expands to more than one machine instruction.  Is that what's happening here---there's an extra machine instruction we're not seeing?  Or bad timing by me?  Not sure.
+I see 11 instructions in the loop, just less than my estimated 12 instructions.
+<1-- Usually we have one assembly instruction per machine instruction (cycle), but sometimes an assembly instruction expands to more than one machine instruction.  Is that what's happening here---there's an extra machine instruction we're not seeing?  Or bad timing by me?  Not sure. -->
 Notice our use of the constant 10,000,000 in the code actually requires two assembly instructions to load the value into register v0:  one for the most significant half-word (16 bits), and one for the least significant half-word.  We have a limit of 32 bits total to specify the instruction (and some of them are used for the opcode and specifying the register).  If we created a variable and assigned it the value 10,000,000, on the other hand, the entire word could be loaded with one lw instruction.

@@ Line 11: / Line 11: @@
 :  0043102a  slt    v0,v0,v1            // if v0 < v1, set v0 to 1, otherwise to 0
 :  1440ffe4  bnez   v0,2fc <main+0x2fc> // if v0 is nonzero (i.e., 10 M <= i), exit "for" loop
-c:  00000000  nop                        // no operation
+c:  00000000  nop                        // no operation; finish branching
 :  8fc20010  lw     v0,16(s8)           // load i into v0
 :  24420001  addiu  v0,v0,1             // (unsigned integer) add 1 to v0
 :  afc20010  sw     v0,16(s8)           // store v0 back to i
 c:  1000fff6  b      358 <main+0x358>    // go back to start of loop, instruction 358
-:  00000000  nop                        // no operation
+:  00000000  nop                        // no operation; finish branching
 </pre>

← Older revision		Revision as of 09:28, 26 January 2011
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	Notice our use of the constant 10,000,000 in the code actually requires two assembly instructions to load the value into register v0: one for the most significant half-word (16 bits), and one for the least significant half-word. We have a limit of 32 bits total to specify the instruction (and some of them are used for the opcode and specifying the register). If we created a variable and assigned it the value 10,000,000, on the other hand, the entire word could be loaded with one lw instruction.		Notice our use of the constant 10,000,000 in the code actually requires two assembly instructions to load the value into register v0: one for the most significant half-word (16 bits), and one for the least significant half-word. We have a limit of 32 bits total to specify the instruction (and some of them are used for the opcode and specifying the register). If we created a variable and assigned it the value 10,000,000, on the other hand, the entire word could be loaded with one lw instruction.

	If you're interested to learn more about assembly instruction sets, you can start with [http://en.wikipedia.org/wiki/MIPS_architecture http://en.wikipedia.org/wiki/MIPS_architecture], or the [[Media:MIPSInstructionReference.pdf\|MIPS Instruction Set Reference]] or [[Media:MIPS-M4K-Core.pdf\|MIPS32 M4K Core Software Reference]]. If you are writing C code that needs to be very time or memory efficient, you can include assembly commands directly in your C code using <tt>asm</tt>. As a simple example, the line <tt>asm("nop")</tt> will directly insert a nop in your compiled code. We will not go into assembly in more detail.		If you're interested to learn more about assembly instruction sets, you can start with [http://en.wikipedia.org/wiki/MIPS_architecture http://en.wikipedia.org/wiki/MIPS_architecture], or the [[Media:MIPSInstructionReference.pdf\|MIPS Instruction Set Reference]] or [[Media:MIPS-M4K-Core.pdf\|MIPS32 M4K Core Software Reference]]. If you are writing C code that needs to be very time or memory efficient, you can include assembly commands directly in your C code using <tt>asm</tt>. As a simple example, the line <tt>asm("nop")</tt> will directly insert a nop in your compiled code. (Though that specific example may not help with efficiency!) We will not go into assembly in more detail.

← Older revision		Revision as of 16:43, 25 January 2011
Line 26:		Line 26:
	Notice our use of the constant 10,000,000 in the code actually requires two assembly instructions to load the value into register v0: one for the most significant half-word (16 bits), and one for the least significant half-word. We have a limit of 32 bits total to specify the instruction (and some of them are used for the opcode and specifying the register). If we created a variable and assigned it the value 10,000,000, on the other hand, the entire word could be loaded with one lw instruction.		Notice our use of the constant 10,000,000 in the code actually requires two assembly instructions to load the value into register v0: one for the most significant half-word (16 bits), and one for the least significant half-word. We have a limit of 32 bits total to specify the instruction (and some of them are used for the opcode and specifying the register). If we created a variable and assigned it the value 10,000,000, on the other hand, the entire word could be loaded with one lw instruction.

	If you're interested to learn more about assembly instruction sets, you can start with [http://en.wikipedia.org/wiki/MIPS_architecture http://en.wikipedia.org/wiki/MIPS_architecture], or the [[Media:MIPSInstructionReference.pdf\|MIPS Instruction Set Reference]] or [[Media:MIPS-M4K-Core.pdf\|MIPS32 M4K Core Software Reference]]. If you are writing code that needs to be very efficient, you can include assembly commands directly in your C code using <tt>asm</tt>. As a simple example, the line <tt>asm("nop");</tt> will directly insert a nop in your compiled code. We will not go into assembly in more detail.		If you're interested to learn more about assembly instruction sets, you can start with [http://en.wikipedia.org/wiki/MIPS_architecture http://en.wikipedia.org/wiki/MIPS_architecture], or the [[Media:MIPSInstructionReference.pdf\|MIPS Instruction Set Reference]] or [[Media:MIPS-M4K-Core.pdf\|MIPS32 M4K Core Software Reference]]. If you are writing code that needs to be very efficient, you can include assembly commands directly in your C code using <tt>asm</tt>. As a simple example, the line <tt>asm("nop")</tt> will directly insert a nop in your compiled code. We will not go into assembly in more detail.

← Older revision		Revision as of 16:42, 25 January 2011
Line 26:		Line 26:
	Notice our use of the constant 10,000,000 in the code actually requires two assembly instructions to load the value into register v0: one for the most significant half-word (16 bits), and one for the least significant half-word. We have a limit of 32 bits total to specify the instruction (and some of them are used for the opcode and specifying the register). If we created a variable and assigned it the value 10,000,000, on the other hand, the entire word could be loaded with one lw instruction.		Notice our use of the constant 10,000,000 in the code actually requires two assembly instructions to load the value into register v0: one for the most significant half-word (16 bits), and one for the least significant half-word. We have a limit of 32 bits total to specify the instruction (and some of them are used for the opcode and specifying the register). If we created a variable and assigned it the value 10,000,000, on the other hand, the entire word could be loaded with one lw instruction.

	If you're interested to learn more about assembly instruction sets, you can start with [http://en.wikipedia.org/wiki/MIPS_architecture http://en.wikipedia.org/wiki/MIPS_architecture], or the [[Media:MIPSInstructionReference.pdf\|MIPS Instruction Set Reference]] or [[Media:MIPS-M4K-Core.pdf\|MIPS32 M4K Core Software Reference]], ~~but~~ we ~~won'~~t go into assembly in more detail.		If you're interested to learn more about assembly instruction sets, you can start with [http://en.wikipedia.org/wiki/MIPS_architecture http://en.wikipedia.org/wiki/MIPS_architecture], or the [[Media:MIPSInstructionReference.pdf\|MIPS Instruction Set Reference]] or [[Media:MIPS-M4K-Core.pdf\|MIPS32 M4K Core Software Reference]]. If you are writing code that needs to be very efficient, you can include assembly commands directly in your C code using <tt>asm</t>. As a simple example, the line <tt>asm("nop");</tt> will directly insert a nop in your compiled code. We will not go into assembly in more detail.