simulator: fix task poll speed

CHANGELOG.md

@@ -14,6 +14,7 @@ customers cannot upgrade their bootloader, its changes are recorded separately.
 - simulator: simulate a Nova device
 - Add API call to fetch multiple xpubs at once
 - Add the option for the simulator to write its memory to file.
+- simulator: spin tasks at max speed instead of at the client poll interval
 
 ### 9.23.1
 - EVM: add HyperEVM (HYPE) and SONIC (S) to known networks

test/simulator/simulator.c

@@ -28,10 +28,12 @@
 #include <unistd.h>
 #include <version.h>
 
+#include <errno.h>
 #include <getopt.h>
 #include <netdb.h>
 #include <netinet/in.h>
 #include <signal.h>
+#include <sys/select.h>
 #include <stdbool.h>
 #include <sys/socket.h>
 
@@ -45,11 +47,6 @@ int commfd;
 static volatile sig_atomic_t sigint_called = false;
 static int sockfd;
 
-static int get_usb_message_socket(uint8_t* input)
-{
-    return read(commfd, input, USB_HID_REPORT_OUT_SIZE);
-}
-
 static void send_usb_message_socket(void)
 {
     const uint8_t* data = queue_pull(queue_hww_queue());
@@ -63,14 +60,6 @@ static void send_usb_message_socket(void)
     }
 }
 
-static void simulate_firmware_execution(const uint8_t* input)
-{
-    usb_packet_process((const USB_FRAME*)input);
-    rust_workflow_spin();
-    rust_async_usb_spin();
-    usb_processing_process(usb_processing_hww());
-}
-
 static void _int_handler(int signum)
 {
     (void)signum;
@@ -170,13 +159,44 @@ int main(int argc, char* argv[])
         }
         printf("Socket connection setup success\n");
 
+        // Set commfd to non-blocking
+        int flags = fcntl(commfd, F_GETFL, 0);
+        if (flags == -1 || fcntl(commfd, F_SETFL, flags | O_NONBLOCK) == -1) {
+            perror("fcntl");
+            close(commfd);
+            continue;
+        }
+
         // BitBox02 firmware loop
         uint8_t input[BUFFER_SIZE];
         int temp_len;
         while (1) {
             // Simulator polls for USB messages from client and then processes them
-            if (!get_usb_message_socket(input)) break;
-            simulate_firmware_execution(input);
+
+            fd_set readfds;
+            FD_ZERO(&readfds);
+            FD_SET(commfd, &readfds);
+             // 0.05ms timeout, so this loop does not lead to 100% CPU usage, but is also not
+             // unbearably slow. It is a trade-off as we don't have proper waking of our Rust tasks,
+             // just busy polling.
+            struct timeval timeout = {0, 500};
+
+            if (select(commfd + 1, &readfds, NULL, NULL, &timeout) < 0) {
+                break;
+            }
+
+            if (FD_ISSET(commfd, &readfds)) {
+                int bytes_read = read(commfd, input, USB_HID_REPORT_OUT_SIZE);
+                if (bytes_read == 0) break;
+                else if (bytes_read > 0) {
+                    usb_packet_process((const USB_FRAME*)input);
+                }
+            }
+
+
+            usb_processing_process(usb_processing_hww());
+            rust_workflow_spin();
+            rust_async_usb_spin();
 
             // If the USB message to be sent from firmware is bigger than one packet,
             // then the simulator sends the message in multiple packets. Packets use