diff --git a/src/main/io/canvas.c b/src/main/io/canvas.c
index 97b12f03d9..5b0973ed90 100644
--- a/src/main/io/canvas.c
+++ b/src/main/io/canvas.c
@@ -67,6 +67,11 @@ int canvasWrite(uint8_t col, uint8_t row, char *string)
     return canvasOutput(MSP_CANVAS, (uint8_t *)buf, len + 4);
 }
 
+uint16_t canvasTxRoom()
+{
+    return mspSerialPushTxRoom();
+}
+
 screenFnVTable_t canvasVTable = {
     canvasBegin,
     canvasEnd,
@@ -74,15 +79,14 @@ screenFnVTable_t canvasVTable = {
     canvasWrite,
     canvasHeartBeat,
     NULL,
+    canvasTxRoom,
 };
 
 void canvasCmsInit(displayPort_t *pPort)
 {
     pPort->rows = 13;
     pPort->cols = 30;
-    pPort->buftime = 23;          // = 256/(115200/10)
-    pPort->bufsize = 192;         // 256 * 3/4 (Be conservative)
-    pPort->VTable = &canvasVTable;
+    pPort->vTable = &canvasVTable;
 }
 
 void canvasInit()
diff --git a/src/main/io/cms.c b/src/main/io/cms.c
index c83a71d286..be7e5186e8 100644
--- a/src/main/io/cms.c
+++ b/src/main/io/cms.c
@@ -107,37 +107,45 @@ int8_t lastCursorPos;
 
 void cmsScreenClear(displayPort_t *instance)
 {
-    instance->VTable->clear();
+    instance->vTable->clear();
     instance->cleared = true;
     lastCursorPos = -1; // XXX Here
 }
 
 void cmsScreenBegin(displayPort_t *instance)
 {
-    instance->VTable->begin();
-    instance->VTable->clear();
+    instance->vTable->begin();
+    instance->vTable->clear();
 }
 
 void cmsScreenEnd(displayPort_t *instance)
 {
-    instance->VTable->end();
+    instance->vTable->end();
 }
 
 int cmsScreenWrite(displayPort_t *instance, uint8_t x, uint8_t y, char *s)
 {
-    return instance->VTable->write(x, y, s);
+    return instance->vTable->write(x, y, s);
 }
 
 void cmsScreenHeartBeat(displayPort_t *instance)
 {
-    if (instance->VTable->heartbeat)
-        instance->VTable->heartbeat();
+    if (instance->vTable->heartbeat)
+        instance->vTable->heartbeat();
 }
 
 void cmsScreenResync(displayPort_t *instance)
 {
-    if (instance->VTable->resync)
-        instance->VTable->resync();
+    if (instance->vTable->resync)
+        instance->vTable->resync();
+}
+
+uint16_t cmsScreenTxRoom(displayPort_t *instance)
+{
+    if (instance->vTable->txroom)
+        return instance->vTable->txroom();
+    else
+        return 10000;
 }
 
 void cmsScreenInit(displayPort_t *pDisp, cmsDeviceInitFuncPtr cmsDeviceInitFunc)
@@ -377,7 +385,7 @@ void cmsDrawMenu(displayPort_t *pDisplay, uint32_t currentTime)
     static uint8_t pollDenom = 0;
     bool drawPolled = (++pollDenom % 8 == 0);
 
-    int16_t cnt = 0;
+    int room = cmsScreenTxRoom(pDisplay);
 
     if (!currentMenu)
         return;
@@ -404,20 +412,26 @@ void cmsDrawMenu(displayPort_t *pDisplay, uint32_t currentTime)
         currentCursorPos++;
 
     if (lastCursorPos >= 0 && currentCursorPos != lastCursorPos) {
-        cnt += cmsScreenWrite(pDisplay, LEFT_MENU_COLUMN, lastCursorPos + top, "  ");
+        room -= cmsScreenWrite(pDisplay, LEFT_MENU_COLUMN, lastCursorPos + top, "  ");
     }
 
+    if (room < 30)
+        return;
+
     if (lastCursorPos != currentCursorPos) {
-        cnt += cmsScreenWrite(pDisplay, LEFT_MENU_COLUMN, currentCursorPos + top, " >");
+        room -= cmsScreenWrite(pDisplay, LEFT_MENU_COLUMN, currentCursorPos + top, " >");
         lastCursorPos = currentCursorPos;
     }
 
+    if (room < 30)
+        return;
+
     // Print text labels
     for (i = 0, p = currentMenu; i < MAX_MENU_ITEMS(pDisplay) && p->type != OME_END; i++, p++) {
         if (IS_PRINTLABEL(p)) {
-            cnt += cmsScreenWrite(pDisplay, LEFT_MENU_COLUMN + 2, i + top, p->text);
+            room -= cmsScreenWrite(pDisplay, LEFT_MENU_COLUMN + 2, i + top, p->text);
             CLR_PRINTLABEL(p);
-            if (cnt > pDisplay->batchsize)
+            if (room < 30)
                 return;
         }
     }
@@ -425,12 +439,12 @@ void cmsDrawMenu(displayPort_t *pDisplay, uint32_t currentTime)
     // Print values
 
     // XXX Polled values at latter positions in the list may not be
-    // XXX printed if the cnt exceeds batchsize in the middle of the list.
+    // XXX printed if not enough room in the middle of the list.
 
     for (i = 0, p = currentMenu; i < MAX_MENU_ITEMS(pDisplay) && p->type != OME_END; i++, p++) {
         if (IS_PRINTVALUE(p)) {
-            cnt += cmsDrawMenuEntry(pDisplay, p, top + i, drawPolled);
-            if (cnt > pDisplay->batchsize)
+            room -= cmsDrawMenuEntry(pDisplay, p, top + i, drawPolled);
+            if (room < 30)
                 return;
         }
     }
@@ -494,12 +508,6 @@ long cmsMenuBack(displayPort_t *pDisplay)
     return 0;
 }
 
-// XXX This should go to device
-void cmsComputeBatchsize(displayPort_t *pDisplay)
-{
-    pDisplay->batchsize = (pDisplay->buftime < CMS_UPDATE_INTERVAL) ? pDisplay->bufsize : (pDisplay->bufsize * CMS_UPDATE_INTERVAL) / pDisplay->buftime;
-}
-
 // XXX Separation
 void cmsx_FeatureRead(void);
 void cmsx_FeatureWriteback(void);
@@ -528,7 +536,6 @@ void cmsMenuOpen(void)
         return;
 
     cmsScreenInit(&currentDisplay, initfunc);
-    cmsComputeBatchsize(&currentDisplay);
     cmsScreenBegin(&currentDisplay);
     cmsMenuChange(&currentDisplay, currentMenu);
 }
diff --git a/src/main/io/cms.h b/src/main/io/cms.h
index a9ab352cd3..76d711a03d 100644
--- a/src/main/io/cms.h
+++ b/src/main/io/cms.h
@@ -7,6 +7,7 @@ typedef struct screenFnVTable_s {
     int (*write)(uint8_t, uint8_t, char *);
     int (*heartbeat)(void);
     void (*resync)(void);
+    uint16_t (*txroom)(void);
 } screenFnVTable_t;
 
 typedef struct displayPort_s {
@@ -14,8 +15,7 @@ typedef struct displayPort_s {
     uint8_t cols;
     uint16_t buftime;
     uint16_t bufsize;
-    uint16_t batchsize;         // Computed by CMS
-    screenFnVTable_t *VTable;
+    screenFnVTable_t *vTable;
 
     // CMS state
     bool cleared;
diff --git a/src/main/io/display.c b/src/main/io/display.c
index d8b5a8b82e..a9fb5c2d3f 100644
--- a/src/main/io/display.c
+++ b/src/main/io/display.c
@@ -783,6 +783,7 @@ screenFnVTable_t displayCmsVTable = {
     displayCmsWrite,
     NULL,
     NULL,
+    NULL,
 };
 
 void displayCmsInit(displayPort_t *pPort)
@@ -791,7 +792,7 @@ void displayCmsInit(displayPort_t *pPort)
     pPort->cols = 21;
     pPort->buftime = 1;
     pPort->bufsize = 50000;
-    pPort->VTable = &displayCmsVTable;
+    pPort->vTable = &displayCmsVTable;
 }
 #endif // OLEDCMS
 
diff --git a/src/main/io/osd.c b/src/main/io/osd.c
index c67c07ce64..7c37b43db8 100755
--- a/src/main/io/osd.c
+++ b/src/main/io/osd.c
@@ -702,6 +702,7 @@ screenFnVTable_t osdVTable = {
     osdWrite,
     NULL,
     max7456RefreshAll,
+    NULL,
 };
 
 void osdCmsInit(displayPort_t *pPort)
@@ -709,8 +710,6 @@ void osdCmsInit(displayPort_t *pPort)
     shiftdown = masterConfig.osdProfile.row_shiftdown;
     pPort->rows = max7456GetRowsCount() - shiftdown;
     pPort->cols = 30;
-    pPort->buftime = 1;         // Very fast
-    pPort->bufsize = 50000;     // Very large
-    pPort->VTable = &osdVTable;
+    pPort->vTable = &osdVTable;
 }
 #endif // OSD
diff --git a/src/main/msp/msp_serial.c b/src/main/msp/msp_serial.c
index ef39598c96..c8d79ecbc9 100644
--- a/src/main/msp/msp_serial.c
+++ b/src/main/msp/msp_serial.c
@@ -246,3 +246,28 @@ void mspSerialPushInit(mspPushCommandFnPtr mspPushCommandFnToUse)
 {
     mspPushCommandFn = mspPushCommandFnToUse;
 }
+
+uint16_t mspSerialPushTxRoom()
+{
+    uint16_t minroom = 50000;
+
+    for (uint8_t portIndex = 0; portIndex < MAX_MSP_PORT_COUNT; portIndex++) {
+        mspPort_t * const mspPort = &mspPorts[portIndex];
+        if (!mspPort->port) {
+            continue;
+        }
+
+        // XXX Kludge!!! Avoid zombie VCP port (avoid VCP entirely for now)
+        if (mspPort->port->identifier == SERIAL_PORT_USB_VCP) {
+            continue;
+        }
+
+        uint32_t room = mspPort->port->vTable->serialTotalTxFree(mspPort->port);
+
+        if (room < minroom) {
+            minroom = room;
+        }
+    }
+
+    return minroom;
+}
diff --git a/src/main/msp/msp_serial.h b/src/main/msp/msp_serial.h
index 5d92114736..11f0d721cf 100644
--- a/src/main/msp/msp_serial.h
+++ b/src/main/msp/msp_serial.h
@@ -68,3 +68,4 @@ void mspSerialAllocatePorts(void);
 void mspSerialReleasePortIfAllocated(struct serialPort_s *serialPort);
 void mspSerialPushInit(mspPushCommandFnPtr mspPushCommandFn);
 void mspSerialPush(uint8_t, uint8_t *, int);
+uint16_t mspSerialPushTxRoom();