sylveos

commit 7da8e0126f36fa58ce158549609bac9061c68aea
parent bdaf157b915565ce2802382e16bf2dfdfcfbcdf4
Author: Sylvia Ivory <git@sivory.net>
Date:   Sat, 31 Jan 2026 01:38:18 -0800

Directly write to Io.Writer for large buffers

Diffstat:
M
pi/devices/mini-uart.zig
 | 
48
+++++++++++++++++++++++++++++++++++++++++++++---

1 file changed, 45 insertions(+), 3 deletions(-)
diff --git a/pi/devices/mini-uart.zig b/pi/devices/mini-uart.zig
@@ -139,6 +139,32 @@ pub fn enable_interrupts() Error!void {
 // var tx_list: std.ArrayList(u8) = .initBuffer(&tx_buffer);
 
 var rx_list: StackRingBuffer(u8, 4096) = .init();
+var rx_writer: ?*std.Io.Writer = null;
+var rx_writer_written: usize = 0;
+
+pub fn switch_rx_writer(rx_w: ?*std.Io.Writer) !void {
+    const cs = mem.enter_critical_section();
+    defer cs.exit();
+
+    rx_writer_written = 0;
+
+    if (rx_w) |w| {
+        // Copy buffer into new writer
+        while (rx_list.pop()) |b| {
+            try w.writeByte(b);
+            rx_writer_written += 1;
+        }
+    }
+
+    rx_writer = rx_w;
+}
+
+pub fn get_rx_written() usize {
+    const cs = mem.enter_critical_section();
+    defer cs.exit();
+
+    return rx_writer_written;
+}
 
 noinline fn uart_handler(pc: usize) void {
     _ = pc;
@@ -156,7 +182,13 @@ noinline fn uart_handler(pc: usize) void {
 
         if ((IIR & 0b100) != 0) {
             // can't do anything with error
-            rx_list.push(read_byte_raw()) catch {};
+            const b = read_byte_raw();
+            if (rx_writer) |w| {
+                rx_writer_written += 1;
+                w.writeByte(b) catch {};
+            } else {
+                rx_list.push(b) catch {};
+            }
         }
 
         // TODO; figure out why TX interrupts aren't working
@@ -310,8 +342,18 @@ fn stream(io_r: *std.Io.Reader, io_w: *std.Io.Writer, limit: std.Io.Limit) !usiz
     _ = io_r;
 
     if (limit.toInt()) |max| {
-        for (0..max) |_| {
-            try io_w.writeByte(read_byte_blocking(null).?);
+        if (max > 128) {
+            // Use direct writes when there's a large buffer
+            try switch_rx_writer(io_w);
+
+            while (get_rx_written() < max) {}
+
+            try switch_rx_writer(null);
+        } else {
+            // Small buffers should just read blocking
+            for (0..max) |_| {
+                try io_w.writeByte(read_byte_blocking(null).?);
+            }
         }
 
         return max;