From 627f05098785327744e666c9149375125499d2ff Mon Sep 17 00:00:00 2001
From: hachem <im@hachem.wtf>
Date: Sun, 4 Oct 2026 00:52:49 +0200
Subject: feat: revelfs type shi

---
 boot/ata.zig | 160 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 160 insertions(+)
 create mode 100644 boot/ata.zig

(limited to 'boot/ata.zig')

diff --git a/boot/ata.zig b/boot/ata.zig
new file mode 100644
index 0000000..ec63c1c
--- /dev/null
+++ b/boot/ata.zig
@@ -0,0 +1,160 @@
+// ata pio driver, primary bus master drive, 28 bit lba
+//
+// this is the dumbest most simple most retartded possible block device driver
+// it busy polls the status port and shovels one sector at a time through the 16
+// bit data port. no dma no interrupts no second drive. its slow but the whole point
+// is that revo builds a real filesystem on top of these two calls (read/write a 512 byte sector) so
+// i need to rewrite this when im not drunk (never gonna happen)
+//
+// see: https://wiki.osdev.org/ATA_PIO_Mode
+
+const port = @import("port.zig");
+const serial = @import("serial.zig");
+
+pub const SECTOR = 512;
+
+// primary bus io ports
+const DATA = 0x1F0;
+const FEATURES = 0x1F1; // error on read
+const SECCOUNT = 0x1F2;
+const LBA_LO = 0x1F3;
+const LBA_MID = 0x1F4;
+const LBA_HI = 0x1F5;
+const DRIVE = 0x1F6;
+const CMD = 0x1F7; // status on read
+const CTRL = 0x3F6; // alt status / device control
+
+// status bits
+const ST_ERR = 0x01;
+const ST_DRQ = 0x08; // data request, drive wants a word moved
+const ST_DRDY = 0x40;
+const ST_BSY = 0x80;
+
+const CMD_READ = 0x20;
+const CMD_WRITE = 0x30;
+const CMD_FLUSH = 0xE7;
+const CMD_IDENTIFY = 0xEC;
+
+var g_present = false;
+var g_sectors: u64 = 0;
+
+pub fn present() bool {
+    return g_present;
+}
+
+pub fn sectorCount() u64 {
+    return g_sectors;
+}
+
+// reading the alt status 4 times burns ~400ns, the spec wants that gap after a
+// command before the status bits mean anything
+fn delay400() void {
+    _ = port.inb(CTRL);
+    _ = port.inb(CTRL);
+    _ = port.inb(CTRL);
+    _ = port.inb(CTRL);
+}
+
+// spin until bsy drops
+// returns false if it never does (dead bus)
+fn waitNotBusy() bool {
+    var spins: u32 = 0;
+    while (spins < 1_000_000) : (spins += 1) {
+        if (port.inb(CMD) & ST_BSY == 0) return true;
+    }
+    return false;
+}
+
+// spin until the drive is ready to move a word (drq set)
+// false on error/timeout
+fn waitDrq() bool {
+    var spins: u32 = 0;
+    while (spins < 1_000_000) : (spins += 1) {
+        const st = port.inb(CMD);
+        if (st & ST_ERR != 0) return false;
+        if (st & ST_BSY == 0 and st & ST_DRQ != 0) return true;
+    }
+    return false;
+}
+
+// select master and load the lba + a one sector count
+fn selectSector(lba: u28) void {
+    port.outb(DRIVE, 0xE0 | @as(u8, @truncate((lba >> 24) & 0x0F)));
+    port.outb(FEATURES, 0);
+    port.outb(SECCOUNT, 1);
+    port.outb(LBA_LO, @truncate(lba & 0xFF));
+    port.outb(LBA_MID, @truncate((lba >> 8) & 0xFF));
+    port.outb(LBA_HI, @truncate((lba >> 16) & 0xFF));
+}
+
+// probe the primary master with identify, the floating bus reads status
+// 0xFF, a present drive clears bsy and coughs up 256 words of identify data,
+// words 60/61 hold the 28 bit sector count
+pub fn init() void {
+    // a nonexistent bus floats high, bail before we wait a million spins on it
+    if (port.inb(CMD) == 0xFF) {
+        serial.write("ata: no drive on primary bus\r\n");
+        return;
+    }
+
+    port.outb(DRIVE, 0xA0); // master
+    delay400();
+    port.outb(SECCOUNT, 0);
+    port.outb(LBA_LO, 0);
+    port.outb(LBA_MID, 0);
+    port.outb(LBA_HI, 0);
+    port.outb(CMD, CMD_IDENTIFY);
+    delay400();
+
+    if (port.inb(CMD) == 0) {
+        serial.write("ata: primary master absent\r\n");
+        return;
+    }
+    if (!waitDrq()) {
+        serial.write("ata: identify failed\r\n");
+        return;
+    }
+
+    var id: [256]u16 = undefined;
+    for (&id) |*w| w.* = port.inw(DATA);
+
+    g_sectors = (@as(u64, id[61]) << 16) | id[60];
+    g_present = true;
+    serial.write("ata: primary master, sectors=");
+    serial.writeDec(g_sectors);
+    serial.write("\r\n");
+}
+
+// read one 512 byte sector at lba into buf
+pub fn read(lba: u28, buf: *[SECTOR]u8) bool {
+    if (!g_present) return false;
+    if (!waitNotBusy()) return false;
+    selectSector(lba);
+    port.outb(CMD, CMD_READ);
+    if (!waitDrq()) return false;
+    var i: usize = 0;
+    while (i < SECTOR) : (i += 2) {
+        const w = port.inw(DATA);
+        buf[i] = @truncate(w & 0xFF);
+        buf[i + 1] = @truncate(w >> 8);
+    }
+    return true;
+}
+
+// write one 512 byte sector from buf to lba, then flush the drive cache so it
+// actually hits the image and survives a reboot, yk, like an actual file system
+pub fn write(lba: u28, buf: *const [SECTOR]u8) bool {
+    if (!g_present) return false;
+    if (!waitNotBusy()) return false;
+    selectSector(lba);
+    port.outb(CMD, CMD_WRITE);
+    if (!waitDrq()) return false;
+    var i: usize = 0;
+    while (i < SECTOR) : (i += 2) {
+        const w = @as(u16, buf[i]) | (@as(u16, buf[i + 1]) << 8);
+        port.outw(DATA, w);
+    }
+    port.outb(CMD, CMD_FLUSH);
+    _ = waitNotBusy();
+    return true;
+}
-- 
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