adiv5_swdp: avoid dead-loop with a sleeping target

A sleeping target continues to communicate over SWD properly but
consistently returns SWDP_ACK_WAIT.

It might be nice to be able to wait for the target to wake up on its
own but if it's not going to wake up, BMP becomes absolutely
unresponsive. Probably the timeout should be made configurable or some
other workaround invented.

Signed-off-by: Paul Fertser <fercerpav@gmail.com>

src/adiv5_swdp.c

@@ -129,10 +129,14 @@ static uint32_t adiv5_swdp_low_access(ADIv5_DP_t *dp, uint8_t APnDP, uint8_t RnW
 	if((addr == 4) || (addr == 8))
 		request ^= 0x20;
 
+	size_t tries = 1000;
 	do {
 		swdptap_seq_out(request, 8);
 		ack = swdptap_seq_in(3);
-	} while(ack == SWDP_ACK_WAIT);
+	} while(--tries && ack == SWDP_ACK_WAIT);
+
+	if(!tries)
+		PLATFORM_FATAL_ERROR(1);
 
 	if(ack == SWDP_ACK_FAULT) {
 		dp->fault = 1;