stm32: Add usbfs double buffer support for bulk rx messages

Implement the usbfs fast buffer switching mechanism on the "bulk out"
endpoint.  This can improve the overall USB throughput and bus
utilization.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

1 files changed, 49 insertions, 14 deletions

diff --git a/src/stm32/usbfs.c b/src/stm32/usbfs.c
index 3c96fd4d..661aa1b1 100644
--- a/src/stm32/usbfs.c
+++ b/src/stm32/usbfs.c
@@ -48,6 +48,12 @@
   #define USB_CNTR_FRES USB_CNTR_USBRST
 #endif
 
+// Some chip variants do not define these fields
+#ifndef USB_EP_DTOG_TX_Pos
+#define USB_EP_DTOG_TX_Pos 6
+#define USB_EP_DTOG_RX_Pos 14
+#endif
+
 
 /****************************************************************
  * USB transfer memory
@@ -110,8 +116,8 @@ btable_configure(void)
     epm_ep_desc_setup(0, BUFRX, USB_CDC_EP0_SIZE);
     epm_ep_desc_setup(USB_CDC_EP_ACM, BUFTX, 0);
     epm_ep_desc_setup(USB_CDC_EP_ACM, BUFRX, 0);
-    epm_ep_desc_setup(USB_CDC_EP_BULK_OUT, BUFTX, 0);
-    epm_ep_desc_setup(USB_CDC_EP_BULK_OUT, BUFRX, USB_CDC_EP_BULK_OUT_SIZE);
+    epm_ep_desc_setup(USB_CDC_EP_BULK_OUT, 0, USB_CDC_EP_BULK_OUT_SIZE);
+    epm_ep_desc_setup(USB_CDC_EP_BULK_OUT, 1, USB_CDC_EP_BULK_OUT_SIZE);
     epm_ep_desc_setup(USB_CDC_EP_BULK_IN, BUFTX, 0);
     epm_ep_desc_setup(USB_CDC_EP_BULK_IN, BUFRX, 0);
 }
@@ -192,20 +198,41 @@ calc_epr_bits(uint32_t epr, uint32_t mask, uint32_t value)
     return (((epr & (EPR_RWBITS | tmask)) ^ tvalue) & ~rwmask) | rwbits | cbits;
 }
 
+// Check if double buffering endpoint hardware can no longer send/receive
+static int
+epr_is_dbuf_blocking(uint32_t epr)
+{
+    return !(((epr >> (USB_EP_DTOG_RX_Pos - USB_EP_DTOG_TX_Pos)) ^ epr)
+             & USB_EP_DTOG_TX);
+}
+
 
 /****************************************************************
  * USB interface
  ****************************************************************/
 
+static uint32_t bulk_out_pop_count, bulk_out_push_flag;
+
 int_fast8_t
 usb_read_bulk_out(void *data, uint_fast8_t max_len)
 {
-    uint32_t ep = USB_CDC_EP_BULK_OUT, epr = USB_EPR[ep];
-    if ((epr & USB_EPRX_STAT) == USB_EP_RX_VALID)
+    if (readl(&bulk_out_push_flag))
         // No data ready
         return -1;
-    uint32_t count = btable_read_packet(ep, BUFRX, data, max_len);
-    USB_EPR[ep] = calc_epr_bits(epr, USB_EPRX_STAT, USB_EP_RX_VALID);
+    uint32_t ep = USB_CDC_EP_BULK_OUT;
+    int bufnum = bulk_out_pop_count & 1;
+    bulk_out_pop_count++;
+    uint32_t count = btable_read_packet(ep, bufnum, data, max_len);
+    writel(&bulk_out_push_flag, USB_EP_DTOG_TX);
+
+    // Check if irq handler pulled another packet before push flag update
+    uint32_t epr = USB_EPR[ep];
+    if (epr_is_dbuf_blocking(epr) && readl(&bulk_out_push_flag)) {
+        // Second packet was already read - must notify hardware
+        writel(&bulk_out_push_flag, 0);
+        USB_EPR[ep] = calc_epr_bits(epr, 0, 0) | USB_EP_DTOG_TX;
+    }
+
     return count;
 }
 
@@ -275,6 +302,9 @@ usb_set_address(uint_fast8_t addr)
 void
 usb_set_configure(void)
 {
+    uint32_t ep = USB_CDC_EP_BULK_OUT;
+    bulk_out_pop_count = 0;
+    USB_EPR[ep] = calc_epr_bits(USB_EPR[ep], USB_EPRX_STAT, USB_EP_RX_VALID);
 }
 
 
@@ -294,8 +324,9 @@ usb_reset(void)
                    | USB_EP_RX_NAK | USB_EP_TX_NAK);
 
     ep = USB_CDC_EP_BULK_OUT;
-    USB_EPR[ep] = (USB_CDC_EP_BULK_OUT | USB_EP_BULK
-                   | USB_EP_RX_VALID | USB_EP_TX_NAK);
+    USB_EPR[ep] = (USB_CDC_EP_BULK_OUT | USB_EP_BULK | USB_EP_KIND
+                   | USB_EP_RX_VALID | USB_EP_TX_NAK | USB_EP_DTOG_TX);
+    bulk_out_push_flag = USB_EP_DTOG_TX;
 
     ep = USB_CDC_EP_BULK_IN;
     USB_EPR[ep] = (USB_CDC_EP_BULK_IN | USB_EP_BULK
@@ -313,18 +344,22 @@ USB_IRQHandler(void)
     if (istr & USB_ISTR_CTR) {
         // Endpoint activity
         uint32_t ep = istr & USB_ISTR_EP_ID, epr = USB_EPR[ep];
-        USB_EPR[ep] = calc_epr_bits(epr, USB_EP_CTR_RX | USB_EP_CTR_TX, 0);
-        if (ep == 0) {
+        if (ep == USB_CDC_EP_BULK_OUT) {
+            USB_EPR[ep] = (calc_epr_bits(epr, USB_EP_CTR_RX | USB_EP_CTR_TX, 0)
+                           | bulk_out_push_flag);
+            bulk_out_push_flag = 0;
+            usb_notify_bulk_out();
+        } else if (ep == USB_CDC_EP_BULK_IN) {
+            USB_EPR[ep] = calc_epr_bits(epr, USB_EP_CTR_RX | USB_EP_CTR_TX, 0);
+            usb_notify_bulk_in();
+        } else if (ep == 0) {
+            USB_EPR[ep] = calc_epr_bits(epr, USB_EP_CTR_RX | USB_EP_CTR_TX, 0);
             usb_notify_ep0();
             if (epr & USB_EP_CTR_TX && set_address) {
                 // Apply address after last "in" message transmitted
                 USB->DADDR = set_address;
                 set_address = 0;
             }
-        } else if (ep == USB_CDC_EP_BULK_OUT) {
-            usb_notify_bulk_out();
-        } else if (ep == USB_CDC_EP_BULK_IN) {
-            usb_notify_bulk_in();
         }
     }
     if (istr & USB_ISTR_RESET) {