Move bootloader reset signal detection to Wirish.

Use usb_cdcacm hooks to move the DTR edge and "1EAF" magic packet
detection to usb_serial.cpp. We'll later be able to extend this system
to support Leonardo-style reset signalling.

Signed-off-by: Marti Bolivar <mbolivar@leaflabs.com>

1 files changed, 116 insertions, 0 deletions

diff --git a/wirish/usb_serial.cpp b/wirish/usb_serial.cpp
index cfc6317..bf2ea4e 100644
--- a/wirish/usb_serial.cpp
+++ b/wirish/usb_serial.cpp
@@ -32,11 +32,23 @@
 
 #include <string.h>
 
+#include <libmaple/nvic.h>
 #include <libmaple/usb_cdcacm.h>
 #include <libmaple/usb.h>
 
 #include <wirish/wirish.h>
 
+/*
+ * Hooks used for bootloader reset signalling
+ */
+
+static void rxHook(unsigned, void*);
+static void ifaceSetupHook(unsigned, void*);
+
+/*
+ * USBSerial interface
+ */
+
 #define USB_TIMEOUT 50
 
 USBSerial::USBSerial(void) {
@@ -48,12 +60,15 @@ USBSerial::USBSerial(void) {
 void USBSerial::begin(void) {
 #if BOARD_HAVE_SERIALUSB
     usb_cdcacm_enable(BOARD_USB_DISC_DEV, BOARD_USB_DISC_BIT);
+    usb_cdcacm_set_hooks(USB_CDCACM_HOOK_RX, rxHook);
+    usb_cdcacm_set_hooks(USB_CDCACM_HOOK_IFACE_SETUP, ifaceSetupHook);
 #endif
 }
 
 void USBSerial::end(void) {
 #if BOARD_HAVE_SERIALUSB
     usb_cdcacm_disable(BOARD_USB_DISC_DEV, BOARD_USB_DISC_BIT);
+    usb_cdcacm_remove_hooks(USB_CDCACM_HOOK_RX | USB_CDCACM_HOOK_IFACE_SETUP);
 #endif
 }
 
@@ -126,3 +141,104 @@ uint8 USBSerial::getRTS(void) {
 #if BOARD_HAVE_SERIALUSB
 USBSerial SerialUSB;
 #endif
+
+/*
+ * Bootloader hook implementations
+ */
+
+enum reset_state_t {
+    DTR_UNSET,
+    DTR_HIGH,
+    DTR_NEGEDGE,
+    DTR_LOW
+};
+
+static reset_state_t reset_state = DTR_UNSET;
+
+static void ifaceSetupHook(unsigned hook, void *requestvp) {
+    uint8 request = *(uint8*)requestvp;
+
+    // Ignore requests we're not interested in.
+    if (request != USB_CDCACM_SET_CONTROL_LINE_STATE) {
+        return;
+    }
+
+    // We need to see a negative edge on DTR before we start looking
+    // for the in-band magic reset byte sequence.
+    uint8 dtr = usb_cdcacm_get_dtr();
+    switch (reset_state) {
+    case DTR_UNSET:
+        reset_state = dtr ? DTR_HIGH : DTR_LOW;
+        break;
+    case DTR_HIGH:
+        reset_state = dtr ? DTR_HIGH : DTR_NEGEDGE;
+        break;
+    case DTR_NEGEDGE:
+        reset_state = dtr ? DTR_HIGH : DTR_LOW;
+        break;
+    case DTR_LOW:
+        reset_state = dtr ? DTR_HIGH : DTR_LOW;
+        break;
+    }
+}
+
+#define RESET_DELAY 100000
+static void wait_reset(void) {
+  delay_us(RESET_DELAY);
+  nvic_sys_reset();
+}
+
+#define STACK_TOP 0x20000800
+#define EXC_RETURN 0xFFFFFFF9
+#define DEFAULT_CPSR 0x61000000
+static void rxHook(unsigned hook, void *ignored) {
+    /* FIXME this is mad buggy; we need a new reset sequence. E.g. NAK
+     * after each RX means you can't reset if any bytes are waiting. */
+    if (reset_state == DTR_NEGEDGE) {
+        reset_state = DTR_LOW;
+
+        if (usb_cdcacm_data_available() >= 4) {
+            // The magic reset sequence is "1EAF".
+            uint8 cmpBuf[4] = {'1', 'E', 'A', 'F'};
+            uint8 chkBuf[4];
+
+            // Peek at the waiting bytes, looking for reset sequence.
+            usb_cdcacm_peek(chkBuf, 4);
+            bool cmpMatch = true;
+            for (int i = 0; i < 4; i++) {
+                if (chkBuf[i] != cmpBuf[i]) {
+                    cmpMatch = false;
+                    break;
+                }
+            }
+
+            // Got the magic sequence? Reset, presumably into the bootloader.
+            if (cmpMatch) {
+                // Return address is wait_reset, but we must set the thumb bit.
+                unsigned int target = (unsigned int)wait_reset | 0x1;
+                asm volatile("mov r0, %[stack_top]      \n\t" // Reset stack
+                             "mov sp, r0                \n\t"
+                             "mov r0, #1                \n\t"
+                             "mov r1, %[target_addr]    \n\t"
+                             "mov r2, %[cpsr]           \n\t"
+                             "push {r2}                 \n\t" // Fake xPSR
+                             "push {r1}                 \n\t" // PC target addr
+                             "push {r0}                 \n\t" // Fake LR
+                             "push {r0}                 \n\t" // Fake R12
+                             "push {r0}                 \n\t" // Fake R3
+                             "push {r0}                 \n\t" // Fake R2
+                             "push {r0}                 \n\t" // Fake R1
+                             "push {r0}                 \n\t" // Fake R0
+                             "mov lr, %[exc_return]     \n\t"
+                             "bx lr"
+                             :
+                             : [stack_top] "r" (STACK_TOP),
+                               [target_addr] "r" (target),
+                               [exc_return] "r" (EXC_RETURN),
+                               [cpsr] "r" (DEFAULT_CPSR)
+                             : "r0", "r1", "r2");
+                /* should never get here */
+            }
+        }
+    }
+}