serial: add writeBuf() and implement for USB.

This lets USB send up to 32 bytes in a frame instead of 32 one byte
frames.  Add a fallback for drivers that don't implement writeBuf().

Signed-off-by: Michael Hope <mlhx@google.com>

src/main/drivers/serial.c

@@ -40,6 +40,17 @@ void serialWrite(serialPort_t *instance, uint8_t ch)
     instance->vTable->serialWrite(instance, ch);
 }
 
+void serialWriteBuf(serialPort_t *instance, void *data, int count)
+{
+    if (instance->vTable->writeBuf) {
+        instance->vTable->writeBuf(instance, data, count);
+    } else {
+        for (uint8_t *p = data; count > 0; count--, p++) {
+            serialWrite(instance, *p);
+        }
+    }
+}
+
 uint8_t serialRxBytesWaiting(serialPort_t *instance)
 {
     return instance->vTable->serialTotalRxWaiting(instance);
@@ -70,14 +81,7 @@ void serialSetMode(serialPort_t *instance, portMode_t mode)
     instance->vTable->setMode(instance, mode);
 }
 
-void serialBeginWrite(serialPort_t *instance)
+void serialWriteBufShim(void *instance, void *data, int count)
 {
-    if (instance->vTable->beginWrite)
-        instance->vTable->beginWrite(instance);
-}
-
-void serialEndWrite(serialPort_t *instance)
-{
-    if (instance->vTable->endWrite)
-        instance->vTable->endWrite(instance);
+    serialWriteBuf((serialPort_t *)instance, data, count);
 }

src/main/drivers/serial.h

@@ -74,14 +74,13 @@ struct serialPortVTable {
 
     void (*setMode)(serialPort_t *instance, portMode_t mode);
 
-    // Optional functions used to buffer large writes.
-    void (*beginWrite)(serialPort_t *instance);
-    void (*endWrite)(serialPort_t *instance);
+    void (*writeBuf)(serialPort_t *instance, void *data, int count);
 };
 
 void serialWrite(serialPort_t *instance, uint8_t ch);
 uint8_t serialRxBytesWaiting(serialPort_t *instance);
 uint8_t serialTxBytesFree(serialPort_t *instance);
+void serialWriteBuf(serialPort_t *instance, void *data, int count);
 uint8_t serialRead(serialPort_t *instance);
 void serialSetBaudRate(serialPort_t *instance, uint32_t baudRate);
 void serialSetMode(serialPort_t *instance, portMode_t mode);
@@ -89,5 +88,5 @@ bool isSerialTransmitBufferEmpty(serialPort_t *instance);
 void serialPrint(serialPort_t *instance, const char *str);
 uint32_t serialGetBaudRate(serialPort_t *instance);
 
-void serialBeginWrite(serialPort_t *instance);
-void serialEndWrite(serialPort_t *instance);
+// A shim that adapts the bufWriter API to the serialWriteBuf() API.
+void serialWriteBufShim(void *instance, void *data, int count);

src/main/drivers/serial_softserial.c

@@ -479,9 +479,8 @@ const struct serialPortVTable softSerialVTable[] = {
         softSerialSetBaudRate,
         isSoftSerialTransmitBufferEmpty,
         softSerialSetMode,
-        .beginWrite = NULL,
-        .endWrite = NULL,
-  }
+        .writeBuf = NULL,
+    }
 };
 
 #endif

src/main/drivers/serial_uart.c

@@ -322,7 +322,6 @@ const struct serialPortVTable uartVTable[] = {
         uartSetBaudRate,
         isUartTransmitBufferEmpty,
         uartSetMode,
-        .beginWrite = NULL,
-        .endWrite = NULL,
+        .writeBuf = NULL,
     }
 };

src/main/drivers/serial_usb_vcp.c

@@ -27,7 +27,6 @@
 #include "usb_core.h"
 #include "usb_init.h"
 #include "hw_config.h"
-#include "common/utils.h"
 
 #include "drivers/system.h"
 
@@ -83,49 +82,30 @@ static uint8_t usbVcpRead(serialPort_t *instance)
     return buf[0];
 }
 
-static bool usbVcpFlush(vcpPort_t *port)
+static void usbVcpWriteBuf(serialPort_t *instance, void *data, int count)
 {
-    uint8_t count = port->txAt;
-    port->txAt = 0;
+    UNUSED(instance);
 
-    if (count == 0) {
-        return true;
+
+    if (!(usbIsConnected() && usbIsConfigured())) {
+        return;
     }
-    if (!usbIsConnected() || !usbIsConfigured()) {
-        return false;
-    }
-    
-    uint32_t txed;
+
     uint32_t start = millis();
+    for (uint8_t *p = data; count > 0; ) {
+        uint32_t txed = CDC_Send_DATA(p, count);
+        count -= txed;
+        p += txed;
 
-    do {
-        txed = CDC_Send_DATA(port->txBuf, count);
-    } while (txed != count && (millis() - start < USB_TIMEOUT));
-
-    return txed == count;
+        if (millis() - start > USB_TIMEOUT) {
+            break;
+        }
+    }
 }
 
 static void usbVcpWrite(serialPort_t *instance, uint8_t c)
 {
-    vcpPort_t *port = container_of(instance, vcpPort_t, port);
-
-    port->txBuf[port->txAt++] = c;
-    if (!port->buffering || port->txAt >= ARRAYLEN(port->txBuf)) {
-        usbVcpFlush(port);
-    }
-}
-
-static void usbVcpBeginWrite(serialPort_t *instance)
-{
-    vcpPort_t *port = container_of(instance, vcpPort_t, port);
-    port->buffering = true;
-}
-
-static void usbVcpEndWrite(serialPort_t *instance)
-{
-    vcpPort_t *port = container_of(instance, vcpPort_t, port);
-    port->buffering = false;
-    usbVcpFlush(port);
+    usbVcpWriteBuf(instance, &c, sizeof(c));
 }
 
 uint8_t usbTxBytesFree() {
@@ -133,7 +113,7 @@ uint8_t usbTxBytesFree() {
     return 255;
 }
 
-const struct serialPortVTable usbVTable[] = { { usbVcpWrite, usbVcpAvailable, usbTxBytesFree, usbVcpRead, usbVcpSetBaudRate, isUsbVcpTransmitBufferEmpty, usbVcpSetMode } };
+const struct serialPortVTable usbVTable[] = { { usbVcpWrite, usbVcpAvailable, usbTxBytesFree, usbVcpRead, usbVcpSetBaudRate, isUsbVcpTransmitBufferEmpty, usbVcpSetMode, .writeBuf = usbVcpWriteBuf } };
 
 serialPort_t *usbVcpOpen(void)
 {

src/main/drivers/serial_usb_vcp.h

@@ -21,12 +21,6 @@
 
 typedef struct {
     serialPort_t port;
-
-    // Buffer used during bulk writes.
-    uint8_t txBuf[20];
-    uint8_t txAt;
-    // Set if the port is in bulk write mode and can buffer.
-    bool buffering;
 } vcpPort_t;
 
 serialPort_t *usbVcpOpen(void);