RP2040: Recover gracefully when DMA is busy at phase change.

Not sure yet why this happens, but no need to crash completely.

lib/ZuluSCSI_platform_RP2040/scsiPhy.cpp

@@ -220,13 +220,21 @@ extern "C" uint32_t scsiEnterPhaseImmediate(int phase)
         scsiLogPhaseChange(phase);
 
         // Select between synchronous vs. asynchronous SCSI writes
+        bool syncstatus = false;
         if (scsiDev.target->syncOffset > 0 && (g_scsi_phase == DATA_IN || g_scsi_phase == DATA_OUT))
         {
-            scsi_accel_rp2040_setSyncMode(scsiDev.target->syncOffset, scsiDev.target->syncPeriod);
+            syncstatus = scsi_accel_rp2040_setSyncMode(scsiDev.target->syncOffset, scsiDev.target->syncPeriod);
         }
         else
         {
-            scsi_accel_rp2040_setSyncMode(0, 0);
+            syncstatus = scsi_accel_rp2040_setSyncMode(0, 0);
+        }
+
+        if (!syncstatus)
+        {
+            // SCSI DMA was not idle, we are in some kind of error state, force bus reset
+            scsiDev.resetFlag = 1;
+            return 0;
         }
 
         if (phase < 0)

lib/ZuluSCSI_platform_RP2040/scsi_accel_rp2040.cpp

@@ -956,9 +956,13 @@ void scsi_accel_rp2040_init()
     irq_set_enabled(DMA_IRQ_0, true);
 }
 
-void scsi_accel_rp2040_setSyncMode(int syncOffset, int syncPeriod)
+bool scsi_accel_rp2040_setSyncMode(int syncOffset, int syncPeriod)
 {
-    assert(g_scsi_dma_state == SCSIDMA_IDLE);
+    if (g_scsi_dma_state != SCSIDMA_IDLE)
+    {
+        logmsg("ERROR: SCSI DMA was in state ", (int)g_scsi_dma_state, " when changing sync mode, forcing bus reset");
+        return false;
+    }
 
     if (syncOffset != g_scsi_dma.syncOffset || syncPeriod != g_scsi_dma.syncPeriod)
     {
@@ -1051,4 +1055,5 @@ void scsi_accel_rp2040_setSyncMode(int syncOffset, int syncPeriod)
         }
     }
 
+    return true;
 }

lib/ZuluSCSI_platform_RP2040/scsi_accel_rp2040.h

@@ -30,7 +30,8 @@ void scsi_accel_rp2040_init();
 // Set SCSI access mode for synchronous transfers
 // Setting syncOffset = 0 enables asynchronous SCSI.
 // Setting syncOffset > 0 enables synchronous SCSI.
-void scsi_accel_rp2040_setSyncMode(int syncOffset, int syncPeriod);
+// Returns false if busy, caller should issue bus reset to recover.
+bool scsi_accel_rp2040_setSyncMode(int syncOffset, int syncPeriod);
 
 // Queue a request to write data from the buffer to SCSI bus.
 // This function typically returns immediately and the request will complete in background.