From 51806b936cf16ebd7d704c50c6aafef4df625f15 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jan=20K=C3=A4berich?= <kaeberic@ibr.cs.tu-bs.de>
Date: Sat, 9 Jan 2021 21:21:47 +0100
Subject: [PATCH] Halt sweep when USB buffer full

---
 .../Application/Drivers/USB/usb.c             |  6 +++-
 .../Application/Drivers/USB/usb.h             |  1 +
 Software/VNA_embedded/Application/VNA.cpp     | 31 ++++++++++++++++++-
 3 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/Software/VNA_embedded/Application/Drivers/USB/usb.c b/Software/VNA_embedded/Application/Drivers/USB/usb.c
index e338759..f1f2ff8 100644
--- a/Software/VNA_embedded/Application/Drivers/USB/usb.c
+++ b/Software/VNA_embedded/Application/Drivers/USB/usb.c
@@ -223,7 +223,7 @@ void usb_init(usbd_recv_callback_t receive_callback) {
 }
 bool usb_transmit(const uint8_t *data, uint16_t length) {
 	// attempt to add data to fifo
-	if(usb_transmit_fifo_level + length > sizeof(usb_transmit_fifo)) {
+	if(length > usb_available_buffer()) {
 		// data won't fit, abort
 		return false;
 	}
@@ -280,3 +280,7 @@ void USB_LP_IRQHandler(void)
 {
   HAL_PCD_IRQHandler(&hpcd_USB_FS);
 }
+
+uint16_t usb_available_buffer() {
+	return sizeof(usb_transmit_fifo) - usb_transmit_fifo_level;
+}
diff --git a/Software/VNA_embedded/Application/Drivers/USB/usb.h b/Software/VNA_embedded/Application/Drivers/USB/usb.h
index fa3a3bb..b8e1d14 100644
--- a/Software/VNA_embedded/Application/Drivers/USB/usb.h
+++ b/Software/VNA_embedded/Application/Drivers/USB/usb.h
@@ -19,6 +19,7 @@ typedef void(*usbd_recv_callback_t)(const uint8_t *buf, uint16_t len);
 
 void usb_init(usbd_recv_callback_t receive_callback);
 bool usb_transmit(const uint8_t *data, uint16_t length);
+uint16_t usb_available_buffer();
 void usb_log(const char *log, uint16_t length);
 
 
diff --git a/Software/VNA_embedded/Application/VNA.cpp b/Software/VNA_embedded/Application/VNA.cpp
index 760b846..1608579 100644
--- a/Software/VNA_embedded/Application/VNA.cpp
+++ b/Software/VNA_embedded/Application/VNA.cpp
@@ -12,6 +12,7 @@
 #include "FreeRTOS.h"
 #include "task.h"
 #include "Util.hpp"
+#include "usb.h"
 
 #define LOG_LEVEL	LOG_LEVEL_INFO
 #define LOG_MODULE	"VNA"
@@ -44,6 +45,10 @@ static_assert(alternativePrescaler * alternativeSamplerate == 102400000UL, "alte
 static constexpr uint16_t alternativePhaseInc = 4096 * HW::IF2 / alternativeSamplerate;
 static_assert(alternativePhaseInc * alternativeSamplerate == 4096 * HW::IF2, "DFT can not be computed for 2.IF when using alternative samplerate");
 
+// Constants for USB buffer overflow prevention
+static constexpr uint16_t maxPointsBetweenHalts = 40;
+static constexpr uint32_t reservedUSBbuffer = maxPointsBetweenHalts * (sizeof(Protocol::Datapoint) + 8 /*USB packet overhead*/);
+
 using namespace HWHAL;
 
 bool VNA::Setup(Protocol::SweepSettings s) {
@@ -106,6 +111,8 @@ bool VNA::Setup(Protocol::SweepSettings s) {
 	// invalidate first entry of IFTable, preventing switing of 2.LO in halted callback
 	IFTable[0].pointCnt = 0xFFFF;
 
+	uint16_t pointsWithoutHalt = 0;
+
 	// Transfer PLL configuration to FPGA
 	for (uint16_t i = 0; i < points; i++) {
 		bool harmonic_mixing = false;
@@ -187,6 +194,17 @@ bool VNA::Setup(Protocol::SweepSettings s) {
 					IFdeviation, (uint32_t ) (freq / 1000000), (uint32_t ) (freq % 1000000));
 		}
 
+		// halt on regular intervals to prevent USB buffer overflow
+		if(!needs_halt) {
+			pointsWithoutHalt++;
+			if(pointsWithoutHalt > maxPointsBetweenHalts) {
+				needs_halt = true;
+			}
+		}
+		if(needs_halt) {
+			pointsWithoutHalt = 0;
+		}
+
 		FPGA::WriteSweepConfig(i, lowband, Source.GetRegisters(),
 				LO1.GetRegisters(), attenuator, freq, FPGA::SettlingTime::us20,
 				FPGA::Samples::SPPRegister, needs_halt);
@@ -350,7 +368,18 @@ void VNA::SweepHalted() {
 		adcShifted = false;
 	}
 
-	FPGA::ResumeHaltedSweep();
+	if(usb_available_buffer() >= reservedUSBbuffer) {
+		// enough space available, can resume immediately
+		FPGA::ResumeHaltedSweep();
+	} else {
+		// USB buffer could potentially overflow before next halted point, wait until more space is available.
+		// This function is called from a low level interrupt, need to dispatch to lower priority to allow USB
+		// handling to continue
+		STM::DispatchToInterrupt([](){
+			while(usb_available_buffer() < reservedUSBbuffer);
+			FPGA::ResumeHaltedSweep();
+		});
+	}
 }
 
 void VNA::Stop() {