1 files changed, 29 insertions, 0 deletions
diff --git a/src/pardes/app.zig b/src/pardes/app.zig
index 2f13865..5b1431f 100644
--- a/src/pardes/app.zig
+++ b/src/pardes/app.zig
@@ -185,6 +185,15 @@ export fn zig_main() noreturn {
         @as(u32, @intCast(heap.len / 1024)),
     });
 
+    // The CPU clock, before anything is timed against it. The bootloader leaves 90 MHz and the
+    // CPLL is already at 360, so this is a divider change that disturbs neither UART0 (XTAL) nor
+    // the systimer (XTAL/2.5) nor the flash interface (SPLL). See hal/clkrst.zig:setCpuFreq.
+    if (config.cpu_mhz != 90) hal.clkrst.setCpuFreq(switch (config.cpu_mhz) {
+        180 => .mhz180,
+        360 => .mhz360,
+        else => .mhz90,
+    });
+
     const rwdt_was_armed = hal.rwdt.disable();
     hal.systimer.init();
     _ = rwdt_was_armed;
@@ -208,6 +217,26 @@ export fn zig_main() noreturn {
         });
         while (true) {}
     }
+
+    // The CPU clock, measured rather than assumed. Every cycle count this firmware reports is
+    // divided by it somewhere, and `src/io/chip.zig` records it as "a measured ~90 MHz" that
+    // nothing here reconfigures - so it is worth printing rather than remembering. The systimer is
+    // XTAL/2.5 = 16 MHz and is NOT derived from the CPU clock (`hal/systimer.zig:31`,
+    // `clk_tree_defs.h:196-198`), which is exactly what makes it a valid reference for measuring it.
+    if (prof) {
+        const t_start = hal.systimer.micros(.unit0) orelse 0;
+        const c_start = soc.cycles();
+        // 50 ms is long enough that the systimer's 16 MHz granularity and the loop's own overhead
+        // are both noise, and short enough to be invisible in a boot.
+        while ((hal.systimer.micros(.unit0) orelse 0) -% t_start < 50_000) {}
+        const elapsed_us = (hal.systimer.micros(.unit0) orelse 0) -% t_start;
+        const elapsed_cy = soc.cycles() - c_start;
+        soc.rom.print("MARK CPU_HZ cycles=%u us=%u khz=%u\r\n", .{
+            @as(u32, @intCast(elapsed_cy)),
+            @as(u32, @intCast(elapsed_us)),
+            @as(u32, @intCast(if (elapsed_us > 0) elapsed_cy * 1000 / elapsed_us else 0)),
+        });
+    }
     soc.rom.print("MARK PARDES_READY\r\n", .{});
 
     var in: [256]u8 = undefined;