wip: rp2040: Add support for PIO's jmp_pin (#174)

This field is a bit tricky: It belongs to the EXECCTRL register, while
most of the other fields can determined based on the directives used in
the assembled program, this one has to be set explicitly. This makes it
so that we have to plumb some way to explicitly set the field. I did
this by making `LoadAndStartProgramOptions` take `ExecOptions`, but this
isn't perfect, because if a user sets other fields, they will be ignored
in favour of the values set in the program.

board-support/raspberrypi-rp2040/src/hal/pio.zig

@@ -83,6 +83,7 @@ pub const ClkDivOptions = struct {
 };
 
 pub const ExecOptions = struct {
+    jmp_pin: u5 = 0,
     wrap: u5 = 31,
     wrap_target: u5 = 0,
     side_pindir: bool = false,
@@ -132,6 +133,7 @@ pub const LoadAndStartProgramOptions = struct {
     clkdiv: ClkDivOptions,
     shift: ShiftOptions = .{},
     pin_mappings: PinMappingOptions = .{},
+    exec: ExecOptions = .{},
 };
 
 pub const Pio = enum(u1) {
@@ -254,18 +256,19 @@ pub const Pio = enum(u1) {
     pub fn sm_set_exec_options(self: Pio, sm: StateMachine, options: ExecOptions) void {
         const sm_regs = self.get_sm_regs(sm);
         sm_regs.execctrl.modify(.{
+            // NOTE: EXEC_STALLED is RO
             .WRAP_BOTTOM = options.wrap_target,
             .WRAP_TOP = options.wrap,
             .SIDE_PINDIR = @intFromBool(options.side_pindir),
             .SIDE_EN = @intFromBool(options.side_set_optional),
+            .JMP_PIN = options.jmp_pin,
 
             // TODO: plug in rest of the options
             // STATUS_N
             // STATUS_SEL
             // OUT_STICKY
             // INLINE_OUT_EN
             // OUT_EN_SEL
-            // JMP_PIN
             // EXEC_STALLED
         });
     }
@@ -514,6 +517,8 @@ pub const Pio = enum(u1) {
                     side_set.optional
                 else
                     false,
+
+                .jmp_pin = options.exec.jmp_pin,
             },
         });
     }