cuda: add adb_autopoll_block() and adb_autopoll_unblock() functions

Ensure that the CUDA buffer is protected from autopoll requests overwriting
its contents whilst existing CUDA requests are in progress.
Signed-off-by: NMark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Tested-by: NFinn Thain <fthain@telegraphics.com.au>
Acked-by: NLaurent Vivier <laurent@vivier.eu>
Message-Id: <20200623204936.24064-17-mark.cave-ayland@ilande.co.uk>

hw/misc/macio/cuda.c

@@ -116,6 +116,7 @@ static void cuda_update(CUDAState *s)
 {
     MOS6522CUDAState *mcs = &s->mos6522_cuda;
     MOS6522State *ms = MOS6522(mcs);
+    ADBBusState *adb_bus = &s->adb_bus;
     int packet_received, len;
 
     packet_received = 0;
@@ -126,6 +127,9 @@ static void cuda_update(CUDAState *s)
             /* data output */
             if ((ms->b & (TACK | TIP)) != (s->last_b & (TACK | TIP))) {
                 if (s->data_out_index < sizeof(s->data_out)) {
+                    if (s->data_out_index == 0) {
+                        adb_autopoll_block(adb_bus);
+                    }
                     trace_cuda_data_send(ms->sr);
                     s->data_out[s->data_out_index++] = ms->sr;
                     cuda_delay_set_sr_int(s);
@@ -140,6 +144,7 @@ static void cuda_update(CUDAState *s)
                     /* indicate end of transfer */
                     if (s->data_in_index >= s->data_in_size) {
                         ms->b = (ms->b | TREQ);
+                        adb_autopoll_unblock(adb_bus);
                     }
                     cuda_delay_set_sr_int(s);
                 }