Calculation for resistor value for mains to speaker

Electricity safety demo

An exercise for us!
	Test questions sometimes look like this...

.section .text
.globl _start

a_function:
	push %ebp
	mov %esp, %ebp
	sub $8, %esp
	movl $100, (%esp)
	movl $20, 4(%esp)
	push $52
	// Draw the stack here
	// Note:  The program will actually crash after this

_start:
	mov %esp, %ebp
	push $82
	call a_function

	int $0x80
	
Next:  Back to our writing numbers example
	Can we open a file and write some numbers to it?
		NOT ascii codes
		So cat will make a mess of the file
		hexcat would be ok

After that:
	Libraries and building things together (chapter 8)
	Let's make a library with our flexible print number function
		And use it to print the numbers in a file
		Clobbering registers

Could we, then, link to a system library and call a C function?
	For sure
	1.  Respect the C calling convention in use
		1a.  Parameters need to be in the right spot
		1b.  Remember register clobbering
		1c.  Look for the return value in the right place
		For 32-bit Linux:
			Parameters go on the stack
			eax, ecx, and edx are clobbered, others are preserved
			Return value will be in eax
	2.  Link to the correct library (ld will need more parameters)
	That's it, let's do it!

A question:
	IF you can either call the C library wrapper or do the system call, which is best?
		Do the system call unless you need the wrapper for something
		More efficent, uses less electricity