Re: baum: NVDA does not detect usb-braille

[Samuel Thibault <samuel.thibault@ens-lyon.org>]

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Re,

Alexander Epaneshnikov, le dim. 18 oct. 2026 22:35:58 +0300, a ecrit:
> On Sun, Oct 18, 2026 at 09:10:39PM +0200, Samuel Thibault wrote:
> > Does the device sends the cell count first or the device identity
> > first?
> 
> I don't know for sure, as I don't have a real Baum display; mine is a
> HumanWare Brailliant, which uses its own protocol. The comment in
> NVDA's driver lists them as "device id, serial number and number of
> cells", so the identity seems to come first, but that is the only hint
> I have. BRLTTY's Baum driver doesn't use 0x15 at all, it asks for each
> of them explicitly.
> 
> NVDA itself doesn't depend on the order: it stores the cell count and
> the identity separately as they arrive and continues once it has both.
> I tested sending the identity first and then the cell count, and NVDA
> detected the display.

Ok, could you check the attached patch?

Thanks,
Samuel

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diff --git a/chardev/baum.c b/chardev/baum.c
index 166d6f2f09..db0a4fff75 100644
--- a/chardev/baum.c
+++ b/chardev/baum.c
@@ -97,6 +97,7 @@ struct BaumChardev {
     brlapi_fileDescriptor brlapi_fd;
     unsigned int x, y;
     bool deferred_init;
+    bool protocol_on;
 
     uint8_t in_buf[BUF_SIZE];
     uint8_t in_buf_used;
@@ -337,13 +338,27 @@ static void baum_write_packet(BaumChardev *baum, const uint8_t *buf, int len)
     }
 }
 
+static void baum_send_cell_count(BaumChardev *baum)
+{
+    uint8_t cell_count[] = { BAUM_RSP_CellCount, baum->x * baum->y };
+    baum_write_packet(baum, cell_count, sizeof(cell_count));
+}
+
+static void baum_send_device_identity(BaumChardev *baum)
+{
+    uint8_t identity[17] = { BAUM_RSP_DeviceIdentity,
+        'B','a','u','m',' ','V','a','r','i','o' };
+    identity[11] = '0' + baum->x / 10;
+    identity[12] = '0' + baum->x % 10;
+    baum_write_packet(baum, identity, sizeof(identity));
+}
+
 /* Called when the other end seems to have a wrong idea of our display size */
 static void baum_cellCount_timer_cb(void *opaque)
 {
     BaumChardev *baum = BAUM_CHARDEV(opaque);
-    uint8_t cell_count[] = { BAUM_RSP_CellCount, baum->x * baum->y };
     DPRINTF("Timeout waiting for DisplayData, sending cell count\n");
-    baum_write_packet(baum, cell_count, sizeof(cell_count));
+    baum_send_cell_count(baum);
 }
 
 /* Try to interpret a whole incoming packet */
@@ -441,17 +456,18 @@ static int baum_eat_packet(BaumChardev *baum, const uint8_t *buf, int len)
         uint8_t protocol;
         DPRINTF("SetProtocol\n");
         EAT(protocol);
-        /* ignore */
+        if (!baum->protocol_on && protocol) {
+            /* Switching on, answer with device identity and cell count */
+            baum_send_device_identity(baum);
+            baum_send_cell_count(baum);
+        }
+        baum->protocol_on = protocol;
         break;
     }
     case BAUM_REQ_GetDeviceIdentity:
     {
-        uint8_t identity[17] = { BAUM_RSP_DeviceIdentity,
-            'B','a','u','m',' ','V','a','r','i','o' };
         DPRINTF("GetDeviceIdentity\n");
-        identity[11] = '0' + baum->x / 10;
-        identity[12] = '0' + baum->x % 10;
-        baum_write_packet(baum, identity, sizeof(identity));
+        baum_send_device_identity(baum);
         break;
     }
     case BAUM_REQ_GetVersionNumber: