From e83071c9fef2d1b347fec4aa41650fe0950c60f8 Mon Sep 17 00:00:00 2001
From: Matt Baker <baker.matt.j@gmail.com>
Date: Sat, 6 Apr 2019 15:12:51 -0700
Subject: [PATCH] lpc176x: force minimum usb disconnect time

Fixes GitHub Issue #1499. Resolves USB hang by forcing a minimum
USB disconnection time at boot.

Signed-off-by: Matt Baker <baker.matt.j@gmail.com>
---
 src/lpc176x/internal.h  |  2 ++
 src/lpc176x/main.c      | 15 +++++++++++++++
 src/lpc176x/usbserial.c |  2 ++
 3 files changed, 19 insertions(+)

diff --git a/src/lpc176x/internal.h b/src/lpc176x/internal.h
index 5dcf99a46..985c30df9 100644
--- a/src/lpc176x/internal.h
+++ b/src/lpc176x/internal.h
@@ -18,4 +18,6 @@ int is_enabled_pclock(uint32_t pclk);
 void enable_pclock(uint32_t pclk);
 void gpio_peripheral(uint32_t gpio, int func, int pullup);
 
+void udelay(uint32_t usecs);
+
 #endif // internal.h
diff --git a/src/lpc176x/main.c b/src/lpc176x/main.c
index 1147faecf..c417a2c72 100644
--- a/src/lpc176x/main.c
+++ b/src/lpc176x/main.c
@@ -7,6 +7,7 @@
 #include "LPC17xx.h" // NVIC_SystemReset
 #include "command.h" // DECL_CONSTANT
 #include "sched.h" // sched_main
+#include "board/misc.h" // timer_read_time
 
 DECL_CONSTANT_STR("MCU", "lpc176x");
 
@@ -66,6 +67,20 @@ command_reset(uint32_t *args)
 }
 DECL_COMMAND_FLAGS(command_reset, HF_IN_SHUTDOWN, "reset");
 
+// Implement simple early-boot delay mechanism
+void
+udelay(uint32_t usecs)
+{
+    if (!(CoreDebug->DEMCR & CoreDebug_DEMCR_TRCENA_Msk)) {
+        CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk;
+        DWT->CTRL |= DWT_CTRL_CYCCNTENA_Msk;
+    }
+
+    uint32_t end = timer_read_time() + timer_from_us(usecs);
+    while (timer_is_before(timer_read_time(), end))
+        ;
+}
+
 // Main entry point
 int
 main(void)
diff --git a/src/lpc176x/usbserial.c b/src/lpc176x/usbserial.c
index 18466da7f..b2e67467a 100644
--- a/src/lpc176x/usbserial.c
+++ b/src/lpc176x/usbserial.c
@@ -277,6 +277,8 @@ usbserial_init(void)
     gpio_peripheral(GPIO(0, 30), 1, 0);
     gpio_peripheral(GPIO(0, 29), 1, 0);
     gpio_peripheral(GPIO(2, 9), 1, 0);
+    // enforce a minimum time bus is disconnected before connecting
+    udelay(5000);
     // setup endpoints
     realize_endpoint(EP0OUT, USB_CDC_EP0_SIZE);
     realize_endpoint(EP0IN, USB_CDC_EP0_SIZE);