From ed4dfd4dc11df6a272c1755d3b2c394e49f66b4f Mon Sep 17 00:00:00 2001
From: Sean Cross <sean@xobs.io>
Date: Mon, 14 Feb 2022 13:52:43 +0800
Subject: [PATCH] emulation: com: update HOLD as part of Transmit

Previously, the HOLD signal was updated in a different clock domain from
the transmission signal. This could result in the HOLD bit being set
even if there was no data available.

Update the HOLD bit if it's present as part of the Transmit cycle.

Signed-off-by: Sean Cross <sean@xobs.io>
---
 emulation/peripherals/Com.cs | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/emulation/peripherals/Com.cs b/emulation/peripherals/Com.cs
index 0544979ec..81187a400 100644
--- a/emulation/peripherals/Com.cs
+++ b/emulation/peripherals/Com.cs
@@ -20,6 +20,7 @@ namespace Antmicro.Renode.Peripherals.SPI
     public interface IComPeripheral : IPeripheral, IInterestingType
     {
         ushort Transmit(ushort data);
+        bool HasData();
         void FinishTransmission();
     }
     public interface IComController : IPeripheral, IInterestingType, IGPIOReceiver
@@ -180,7 +181,15 @@ namespace Antmicro.Renode.Peripherals.SPI
                 // We don't use a separate time domain here because the peripheral's output is buffered and we
                 // want it to operate at the same speed as the host. If we used a separate time domain then there would
                 // be gaps in the buffer, whereas the real hardware will have no gaps.
-                return peripheral.Transmit(data);
+                ushort result = peripheral.Transmit(data);
+
+                // Update the hold GPIO in this same domain. It may get updated slightly in the future
+                // by the `OnGPIO` call above, but update it in this cycle to avoid latency issues.
+                if (holdGpio != null)
+                {
+                    holdGpio.Set(!peripheral.HasData());
+                }
+                return result;
             }
         }
 
@@ -338,7 +347,7 @@ namespace Antmicro.Renode.Peripherals.SPI
             {
                 TxValue = 0xDDDD;
             }
-            this.Log(LogLevel.Debug, "EC received:{0:X4} sent:{1:X4}", value, TxValue);
+            this.Log(LogLevel.Noisy, "EC received:{0:X4} sent:{1:X4}", value, TxValue);
             Hold.Set(!EcRam.WriteFifoHasData());
             EcRam.WriteNextWord((ushort)value);
             // this.Log(LogLevel.Info, "EcRam.ReadFifo now contains {0} items, EcRam.WriteFifo contains {1} items", EcRam.ReadFifoCount(), EcRam.WriteFifoCount());
@@ -350,6 +359,11 @@ namespace Antmicro.Renode.Peripherals.SPI
             // this.Log(LogLevel.Info, "EC finished transmission");
         }
 
+        public bool HasData()
+        {
+            return EcRam.WriteFifoHasData();
+        }
+
         public void Reset()
         {
             EcRam.Reset();
@@ -389,7 +403,7 @@ namespace Antmicro.Renode.Peripherals.SPI
                     // }
                     Rx.Value = (uint)RegisteredPeripheral.Transmit((ushort)val);
                     RegisteredPeripheral.FinishTransmission();
-                    machine.Log(LogLevel.Debug, "SoC sent {0:X4} received {1:X4}", val, Rx.Value);
+                    machine.Log(LogLevel.Noisy, "SoC sent {0:X4} received {1:X4}", val, Rx.Value);
                     if (IntEna.Value)
                     {
                         SpiIntStatus.Value = true;