diff --git a/piolib/examples/apitest.c b/piolib/examples/apitest.c
index 2f6597d..ba1ecb3 100644
--- a/piolib/examples/apitest.c
+++ b/piolib/examples/apitest.c
@@ -184,7 +184,7 @@ int main(int argc, const char **argv) {
         pio_panic("RX FIFO is not empty");
 
     offset = pio_add_program(pio, &genseq_program);
-    pio_sm_config_xfer(pio, sm, PIO_DIR_FROM_SM, 256, 1);
+    pio_sm_config_xfer(pio, sm, PIO_DIR_FROM_SM, 4096, 2);
 
     pio_gpio_init(pio, gpio);
     pio_sm_set_consecutive_pindirs(pio, sm, gpio, 1, true);
@@ -219,6 +219,24 @@ int main(int argc, const char **argv) {
         sleep_ms(10);
     }
 
+    if (!ret)
+    {
+        const uint32_t words = 0x10000;
+        uint32_t *bigbuf = malloc(words * sizeof(bigbuf[0]));
+
+        pio_sm_put_blocking(pio, sm, words - 1);
+        ret = pio_sm_xfer_data(pio, sm, PIO_DIR_FROM_SM, words * sizeof(bigbuf[0]), bigbuf);
+        if (!ret) {
+            for (i = words - 1; i >= 0; i--)
+            {
+                int v = bigbuf[words - 1 - i];
+                if (v != i)
+                    printf(" %x: %x\n", i, v);
+            }
+        }
+        free(bigbuf);
+    }
+
     if (ret)
         printf("* error %d\n", ret);
     return ret;
diff --git a/piolib/include/rp1_pio_if.h b/piolib/include/rp1_pio_if.h
index 84e749e..22f6d84 100644
--- a/piolib/include/rp1_pio_if.h
+++ b/piolib/include/rp1_pio_if.h
@@ -164,6 +164,14 @@ struct rp1_pio_sm_xfer_data_args {
     uint16_t sm;
     uint16_t dir;
     uint16_t data_bytes;
+    uint16_t rsvd;
+    void *data;
+};
+
+struct rp1_pio_sm_xfer_data32_args {
+    uint16_t sm;
+    uint16_t dir;
+    uint32_t data_bytes;
     void *data;
 };
 
@@ -177,10 +185,7 @@ struct rp1_access_hw_args {
 
 #define PIO_IOC_SM_CONFIG_XFER _IOW(PIO_IOC_MAGIC, 0, struct rp1_pio_sm_config_xfer_args)
 #define PIO_IOC_SM_XFER_DATA _IOW(PIO_IOC_MAGIC, 1, struct rp1_pio_sm_xfer_data_args)
-
-#ifdef CONFIG_COMPAT
-//XXX #define PIO_IOC_SM_XFER_DATA32 _IOW(PIO_IOC_MAGIC, 2, struct pio_sm_xfer_data_args)
-#endif
+#define PIO_IOC_SM_XFER_DATA32 _IOW(PIO_IOC_MAGIC, 2, struct rp1_pio_sm_xfer_data32_args)
 
 #define PIO_IOC_READ_HW _IOW(PIO_IOC_MAGIC, 8, struct rp1_access_hw_args)
 #define PIO_IOC_WRITE_HW _IOW(PIO_IOC_MAGIC, 9, struct rp1_access_hw_args)
diff --git a/piolib/pio_rp1.c b/piolib/pio_rp1.c
index 41e1f66..a601ef0 100644
--- a/piolib/pio_rp1.c
+++ b/piolib/pio_rp1.c
@@ -264,10 +264,14 @@ static int rp1_pio_sm_config_xfer(PIO pio, uint sm, uint dir, uint buf_size, uin
 
 static int rp1_pio_sm_xfer_data(PIO pio, uint sm, uint dir, uint data_bytes, void *data)
 {
-    struct rp1_pio_sm_xfer_data_args args = { .sm = sm, .dir = dir, .data_bytes = data_bytes, .data = data };
+    struct rp1_pio_sm_xfer_data_args args = { .sm = sm, .dir = dir, .data_bytes = data_bytes, .rsvd = 0, .data = data };
+    struct rp1_pio_sm_xfer_data32_args args32 = { .sm = sm, .dir = dir, .data_bytes = data_bytes, .data = data };
     int err;
     check_sm_param(sm);
-    err = rp1_ioctl(pio, PIO_IOC_SM_XFER_DATA, &args);
+    if (data_bytes > 0xffff)
+        err = rp1_ioctl(pio, PIO_IOC_SM_XFER_DATA32, &args32);
+    else
+        err = rp1_ioctl(pio, PIO_IOC_SM_XFER_DATA, &args);
     return (err > 0);
 }