From e8f7f8ef9c8063bd60920f42cce2daa22c4fe9e0 Mon Sep 17 00:00:00 2001
From: Sebastien Bourdeauducq <sb@m-labs.hk>
Date: Wed, 19 Apr 2017 10:59:12 +0800
Subject: [PATCH] DMA: speed up playback
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Time reduced from 1.53µs to 1.37µs.
---
 artiq/firmware/ksupport/lib.rs     | 28 +++++++++++++++-------------
 artiq/test/coredevice/test_rtio.py |  2 +-
 2 files changed, 16 insertions(+), 14 deletions(-)

diff --git a/artiq/firmware/ksupport/lib.rs b/artiq/firmware/ksupport/lib.rs
index ea782f21b..69d6846df 100644
--- a/artiq/firmware/ksupport/lib.rs
+++ b/artiq/firmware/ksupport/lib.rs
@@ -398,19 +398,21 @@ extern fn dma_playback(timestamp: i64, ptr: i32) {
         csr::cri_con::selected_write(0);
 
         let status = csr::rtio_dma::error_status_read();
-        let timestamp = csr::rtio_dma::error_timestamp_read();
-        let channel = csr::rtio_dma::error_channel_read();
-        if status & rtio::RTIO_O_STATUS_UNDERFLOW != 0 {
-            csr::rtio_dma::error_underflow_reset_write(1);
-            raise!("RTIOUnderflow",
-                "RTIO underflow at {0} mu, channel {1}",
-                timestamp as i64, channel as i64, 0)
-        }
-        if status & rtio::RTIO_O_STATUS_SEQUENCE_ERROR != 0 {
-            csr::rtio_dma::error_sequence_error_reset_write(1);
-            raise!("RTIOSequenceError",
-                "RTIO sequence error at {0} mu, channel {1}",
-                timestamp as i64, channel as i64, 0)
+        if status != 0 {
+            let timestamp = csr::rtio_dma::error_timestamp_read();
+            let channel = csr::rtio_dma::error_channel_read();
+            if status & rtio::RTIO_O_STATUS_UNDERFLOW != 0 {
+                csr::rtio_dma::error_underflow_reset_write(1);
+                raise!("RTIOUnderflow",
+                    "RTIO underflow at {0} mu, channel {1}",
+                    timestamp as i64, channel as i64, 0)
+            }
+            if status & rtio::RTIO_O_STATUS_SEQUENCE_ERROR != 0 {
+                csr::rtio_dma::error_sequence_error_reset_write(1);
+                raise!("RTIOSequenceError",
+                    "RTIO sequence error at {0} mu, channel {1}",
+                    timestamp as i64, channel as i64, 0)
+            }
         }
     }
 }
diff --git a/artiq/test/coredevice/test_rtio.py b/artiq/test/coredevice/test_rtio.py
index 0aff9b979..d0ee3cec5 100644
--- a/artiq/test/coredevice/test_rtio.py
+++ b/artiq/test/coredevice/test_rtio.py
@@ -605,7 +605,7 @@ class DMATest(ExperimentCase):
         exp.playback_many(count)
         dt = self.dataset_mgr.get("dma_playback_time")
         print("dt={}, dt/count={}".format(dt, dt/count))
-        self.assertLess(dt/count, 7*us)
+        self.assertLess(dt/count, 3*us)
 
     def test_handle_invalidation(self):
         exp = self.create(_DMA)