From 7cd008a0038bf503bee5b7641a1b4afbc85419d3 Mon Sep 17 00:00:00 2001
From: Kyle Schwarz <kschwarz@intrepidcs.com>
Date: Tue, 25 Aug 2020 16:14:47 -0400
Subject: [PATCH] Switch to non-blocking I/O for STM32

STM32 can latency is not as good as it could be when it is synchronous due to read() timeouts,
so switch to asynchronous reading with select().
---
 platform/posix/stm32.cpp | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/platform/posix/stm32.cpp b/platform/posix/stm32.cpp
index bb5b32a..d3c0977 100644
--- a/platform/posix/stm32.cpp
+++ b/platform/posix/stm32.cpp
@@ -10,6 +10,7 @@
 #include <fcntl.h>
 #include <unistd.h>
 #include <errno.h>
+#include <sys/select.h>
 
 using namespace icsneo;
 
@@ -25,7 +26,7 @@ bool STM32::open() {
 		return false;
 	}
 
-	fd = ::open(ttyPath.c_str(), O_RDWR | O_NOCTTY | O_SYNC);
+	fd = ::open(ttyPath.c_str(), O_RDWR | O_NOCTTY | O_NONBLOCK);
 	if(!isOpen()) {
 		//std::cout << "Open of " << ttyPath.c_str() << " failed with " << strerror(errno) << ' ';
 		report(APIEvent::Type::DriverFailedToOpen, APIEvent::Severity::Error);
@@ -113,10 +114,15 @@ bool STM32::close() {
 }
 
 void STM32::readTask() {
-	constexpr size_t READ_BUFFER_SIZE = 8;
+	constexpr size_t READ_BUFFER_SIZE = 2048;
 	uint8_t readbuf[READ_BUFFER_SIZE];
 	EventManager::GetInstance().downgradeErrorsOnCurrentThread();
 	while(!closing) {
+		fd_set rfds = {0};
+		struct timeval tv = {0};
+		FD_SET(fd, &rfds);
+		tv.tv_usec = 50000; // 50ms
+		::select(fd + 1, &rfds, NULL, NULL, &tv);
 		auto bytesRead = ::read(fd, readbuf, READ_BUFFER_SIZE);
 		if(bytesRead > 0)
 			readQueue.enqueue_bulk(readbuf, bytesRead);