From 8c6fc0c15415b32080a848bbde640e104098cf13 Mon Sep 17 00:00:00 2001
From: Carlos Maiolino <cem@maiolino.dev>
Date: Thu, 10 Jul 2025 22:18:39 +0200
Subject: Initial drop

Add some riscv code

Signed-off-by: Carlos Maiolino <cem@toxiclabs.cc>
---
 riscv/riscv-probe/libfemto/drivers/htif.c | 91 +++++++++++++++++++++++++++++++
 1 file changed, 91 insertions(+)
 create mode 100644 riscv/riscv-probe/libfemto/drivers/htif.c

(limited to 'riscv/riscv-probe/libfemto/drivers/htif.c')

diff --git a/riscv/riscv-probe/libfemto/drivers/htif.c b/riscv/riscv-probe/libfemto/drivers/htif.c
new file mode 100644
index 0000000..ef6995e
--- /dev/null
+++ b/riscv/riscv-probe/libfemto/drivers/htif.c
@@ -0,0 +1,91 @@
+// See LICENSE for license details.
+
+#ifdef __riscv
+
+#include "femto.h"
+#include "spinlock.h"
+
+struct { uint32_t arr[2]; } volatile tohost __attribute__((section(".htif")));
+struct { uint32_t arr[2]; } volatile fromhost __attribute__((section(".htif")));
+
+static spinlock_t htif_lock = SPINLOCK_INIT;
+
+static inline void htif_send(uint8_t dev, uint8_t cmd, int64_t data)
+{
+    /* endian neutral encoding with ordered 32-bit writes */
+    union { uint32_t arr[2]; uint64_t val; } encode = {
+        .val = (uint64_t)dev << 56 | (uint64_t)cmd << 48 | data
+    };
+    tohost.arr[0] = encode.arr[0];
+    tohost.arr[1] = encode.arr[1];
+}
+
+static inline void htif_recv(uint8_t *dev, uint8_t *cmd, int64_t *data)
+{
+    /* endian neutral decoding with ordered 32-bit reads */
+    union { uint32_t arr[2]; uint64_t val; } decode;
+    decode.arr[0] = fromhost.arr[0];
+    decode.arr[1] = fromhost.arr[1];
+    *dev = decode.val >> 56;
+    *cmd = (decode.val >> 48) & 0xff;
+    *data = decode.val << 16 >> 16;
+}
+
+static int64_t htif_get_fromhost(uint8_t dev, uint8_t cmd)
+{
+    /* receive data for specified device and command */
+    uint8_t rdev, rcmd;
+    int64_t data;
+    htif_recv(&rdev, &rcmd, &data);
+    return rdev == dev && rcmd == cmd ? data : -1;
+}
+
+static void htif_set_tohost(uint8_t dev, uint8_t cmd, int64_t data)
+{
+    /* send data with specified device and command */
+    while (tohost.arr[0]) {
+        asm volatile ("" : : "r" (fromhost.arr[0]));
+        asm volatile ("" : : "r" (fromhost.arr[1]));
+    }
+    htif_send(dev, cmd, data);
+}
+
+static int htif_getchar()
+{
+    int ch;
+    spinlock_lock(&htif_lock);
+    if ((ch = htif_get_fromhost(1, 0) & 0xff)) {
+        htif_set_tohost(1, 0, 0);
+    }
+    spinlock_unlock(&htif_lock);
+    return ch;
+}
+
+static int htif_putchar(int ch)
+{
+    spinlock_lock(&htif_lock);
+    htif_set_tohost(1, 1, ch & 0xff);
+    spinlock_unlock(&htif_lock);
+    return ch & 0xff;
+}
+
+static void htif_poweroff(int status)
+{
+    for (;;) {
+        htif_set_tohost(0, 0, 1);
+    }
+}
+
+console_device_t console_htif = {
+    NULL,
+    htif_getchar,
+    htif_putchar
+};
+
+
+poweroff_device_t poweroff_htif = {
+    NULL,
+    htif_poweroff
+};
+
+#endif
-- 
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