Emulating a CPU in C++ #17 (6502) - BEQ Conditional Branch

In this episde i get one of the conditional branch instruction working BEQ - Branch on equal to zero.
Links:
Source for this project: github.com/davepoo/6502Emulator
Google Test: github.com/google/googletest
6502 Information: www.obelisk.me.uk/6502/
Timestamps:
0:00 Intro
3:11 BEQ unit test
9:03 First implementation
10:48 More tests
11:57 Improving implementation
12:30 Cross a page test
15:01 Fixing page cross cycles
21:08 Branch backwards test
23:50 Fixing branch backwards
26:26 No branching test
27:49 Writing a test program
30:55 Closing comments

[@christianlett]

Crossing a page boundary adds two cycles to the base 2 cycles to give a total of 4 cycles, not 5 cycles as you've written here. So it's either 2 (branch unsuccessful), 3 (branch successful), or 4 (branch successful crossing a page boundary) cycles. Apologies if you've fixed this in a later video :)

[@M4RC90]

25:35 It is not defined in the standard that 'char' is always signed. This works with your compiler, it might not with another, or different settings. To make this clear it should be 'signed char' instead. Interesting fact: char, signed char and unsigned char are three distinct types.

[@DavePoo]

Signed is the default if ommited

[@M4RC90]

@@DavePoo not for char, everything else that's true

[@starsky51]

Loving the series (so far), Dave. I'm not a serious coder, but watching you chip away at the instruction set is inspirational!

[@DavePoo]

Thanks. I think that was one of the ideas behind doing to this on video (which i said i wasn't going to do in the first video!) was to show that coding is just "chip away at it until it works".

[@MatthewWalker0]

The effects of simulating a state machine (ie. the real hardware) as a single switch statement are becoming more apparent, with all these cycle & PC problems :)

[@64jcl]

See you did a couple of errors setting the PC on the reset so a suggestion could be to just define a base variable in your tests and do mem[base] = .. , mem[base+1] , so it becomes easer to move this address around for each test?