Watches and Breakpoints

Expressions are used while debugging to show the state of the machine in the Watch window, to set conditional and hit-count breakpoints, to set logpoints, and to write function breakpoints like vram(...) and vsync(...).

The expressions are C#, and are based on the variables shown in the debugger. The roots match the sections in the Variables window with any spaces removed: CPU, VERA, Kernal, Display, I2C, SMC, RTC, VIA, SDCard and more.

Because expressions are C# code, they are case sensitive.

For example the CPU’s registers and flags:

CPU.A
CPU.X
CPU.Y
CPU.PC
CPU.SP
CPU.Flags.Zero
CPU.Flags.Carry

Which matches up to the Variables window:

CPU registers and flags in the Variables window

Memory can be queried as an array. For example to read a single byte:

CPU.Ram[0x0000]
VERA.VRam[0x00000]

Arrays have additional functionality to allow us to see a value at a position as if it were other data types.

CPU.Ram[0x0000].Byte                // 8 bit integer
CPU.Ram[0x0000].Sbyte               // Signed 8 bit integer
CPU.Ram[0x0000].Char                // Character
CPU.Ram[0x0000].Short               // 16 bit integer
CPU.Ram[0x0000].Ushort              // Unsigned 16 bit integer
CPU.Ram[0x0000].Int                 // 32 bit integer
CPU.Ram[0x0000].Uint                // Unsigned 32 bit integer
CPU.Ram[0x0000].Long                // 64 bit integer
CPU.Ram[0x0000].Ulong               // Unsigned 64 bit integer
CPU.Ram[0x0000].String              // Null terminated string
CPU.Ram[0x0000].FixedString(10)     // Fixed length string

For example the Watch window showing a 32 bit integer and a string:

A 32-bit integer and a string shown in the Watch window

As this is a C# expression, the offset doesn’t need to be a constant, but can be an expression. These are all valid:

CPU.Ram[CPU.X]
CPU.Ram[CPU.Y * 2 + 100]
VERA.VRam[CPU.X * CPU.Y]

Conditional breakpoints

Conditional breakpoints will evaluate the expression and check if the result is ‘truthy’. The breakpoint is considered hit if the value is true, non-zero or a non-blank string.

A conditional breakpoint being set and hit

Hit count breakpoints

Hit count breakpoints work like conditional breakpoints, but the number of times a breakpoint has been hit is added to the beginning of the expression.

For example a hit count breakpoint of == 10 would become x == 10, where x is an integer. Again the truthy value rules are applied.

Hit count breakpoints can be combined with conditional breakpoints for extra flexibility, however both need to be true for the breakpoint to hit.

A hit count breakpoint being set and hit

Logpoints

Logpoints will display a message in the Debug Console when they are hit, which is especially useful for a system where outputting text natively is difficult.

Logpoints can be combined with conditional and hit count breakpoints to determine if the output will be logged.

The string is a C# formatted string, and can bring in the system variables like any other expression.

A logpoint printing a message to the Debug Console

Performance

Performance of breakpoints with an expression is poor: each hit stops the X16 and updates the debugger’s view of machine state before the expression is even evaluated. Use them sparingly, and disable them when you’re not using them.