Update USBTMC driver to support dynamic packet sizes (based on descriptor).

src/class/usbtmc/usbtmc_device.c

@@ -64,7 +64,8 @@
 // USBTMC 3.2.2 error conditions not strictly followed
 // No local lock-out, REN, or GTL.
 // Clear message available status byte at the correct time? (488 4.3.1.3)
-
+// Ability to defer status byte transmission
+// Transmission of status byte in response to USB488 SRQ condition
 
 #include "tusb_option.h"
 
@@ -80,6 +81,11 @@
 static char logMsg[150];
 #endif
 
+// Buffer size must be an exact multiple of the max packet size for both
+// bulk  (up to 64 bytes for FS, 512 bytes for HS). In addation, this driver
+// imposes a minimum buffer size of 32 bytes. 
+#define USBTMCD_BUFFER_SIZE (TUD_OPT_HIGH_SPEED ? 512 : 64)
+
 /*
  * The state machine does not allow simultaneous reading and writing. This is
  * consistent with USBTMC.
@@ -120,9 +126,12 @@ typedef struct
   uint8_t ep_int_in;
   // IN buffer is only used for first packet, not the remainder
   // in order to deal with prepending header
-  CFG_TUSB_MEM_ALIGN uint8_t ep_bulk_in_buf[USBTMCD_MAX_PACKET_SIZE];
+  CFG_TUSB_MEM_ALIGN uint8_t ep_bulk_in_buf[USBTMCD_BUFFER_SIZE];
+  uint32_t ep_bulk_in_wMaxPacketSize;
   // OUT buffer receives one packet at a time
-  CFG_TUSB_MEM_ALIGN uint8_t ep_bulk_out_buf[USBTMCD_MAX_PACKET_SIZE];
+  CFG_TUSB_MEM_ALIGN uint8_t ep_bulk_out_buf[USBTMCD_BUFFER_SIZE];
+  uint32_t ep_bulk_out_wMaxPacketSize;
+
   uint32_t transfer_size_remaining; // also used for requested length for bulk IN.
   uint32_t transfer_size_sent;      // To keep track of data bytes that have been queued in FIFO (not header bytes)
 
@@ -139,11 +148,8 @@ CFG_TUSB_MEM_SECTION static usbtmc_interface_state_t usbtmc_state =
     .itf_id = 0xFF,
 };
 
-// We need all headers to fit in a single packet in this implementation.
-TU_VERIFY_STATIC(USBTMCD_MAX_PACKET_SIZE >= 32u,"USBTMC dev EP packet size too small");
-TU_VERIFY_STATIC(
-    (sizeof(usbtmc_state.ep_bulk_in_buf) % USBTMCD_MAX_PACKET_SIZE) == 0,
-    "packet buffer must be a multiple of the packet size");
+// We need all headers to fit in a single packet in this implementation, 32 bytes will fit all standard USBTMC headers
+TU_VERIFY_STATIC(USBTMCD_BUFFER_SIZE >= 32u,"USBTMC dev buffer size too small");
 
 static bool handle_devMsgOutStart(uint8_t rhport, void *data, size_t len);
 static bool handle_devMsgOut(uint8_t rhport, void *data, size_t len, size_t packetLen);
@@ -151,7 +157,6 @@ static bool handle_devMsgOut(uint8_t rhport, void *data, size_t len, size_t pack
 static uint8_t termChar;
 static uint8_t termCharRequested = false;
 
-
 osal_mutex_def_t usbtmcLockBuffer;
 static osal_mutex_t usbtmcLock;
 
@@ -282,12 +287,15 @@ uint16_t usbtmcd_open_cb(uint8_t rhport, tusb_desc_interface_t const * itf_desc,
       tusb_desc_endpoint_t const *ep_desc = (tusb_desc_endpoint_t const *)p_desc;
       switch(ep_desc->bmAttributes.xfer) {
         case TUSB_XFER_BULK:
-          TU_ASSERT(tu_edpt_packet_size(ep_desc) == USBTMCD_MAX_PACKET_SIZE, 0);
+          // Ensure  buffer is an exact multiple of the maxPacketSize
+          TU_ASSERT((USBTMCD_BUFFER_SIZE % tu_edpt_packet_size(ep_desc)) == 0, 0);
           if (tu_edpt_dir(ep_desc->bEndpointAddress) == TUSB_DIR_IN)
           {
             usbtmc_state.ep_bulk_in = ep_desc->bEndpointAddress;
+            usbtmc_state.ep_bulk_in_wMaxPacketSize = tu_edpt_packet_size(ep_desc);
           } else {
             usbtmc_state.ep_bulk_out = ep_desc->bEndpointAddress;
+            usbtmc_state.ep_bulk_out_wMaxPacketSize = tu_edpt_packet_size(ep_desc);
           }
 
           break;
@@ -395,7 +403,7 @@ static bool handle_devMsgOut(uint8_t rhport, void *data, size_t len, size_t pack
   // return true upon failure, as we can assume error is being handled elsewhere.
   TU_VERIFY(usbtmc_state.state == STATE_RCV,true);
 
-  bool shortPacket = (packetLen < USBTMCD_MAX_PACKET_SIZE);
+  bool shortPacket = (packetLen < usbtmc_state.ep_bulk_out_wMaxPacketSize);
 
   // Packet is to be considered complete when we get enough data or at a short packet.
   bool atEnd = false;
@@ -522,7 +530,7 @@ bool usbtmcd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t result, uint
       break;
 
     case STATE_TX_INITIATED:
-      if(usbtmc_state.transfer_size_remaining >=sizeof(usbtmc_state.ep_bulk_in_buf))
+      if(usbtmc_state.transfer_size_remaining >= sizeof(usbtmc_state.ep_bulk_in_buf))
       {
         // FIXME! This removes const below!
         TU_VERIFY( usbd_edpt_xfer(rhport, usbtmc_state.ep_bulk_in,
@@ -539,7 +547,7 @@ bool usbtmcd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t result, uint
         usbtmc_state.transfer_size_remaining = 0;
         usbtmc_state.devInBuffer = NULL;
         TU_VERIFY( usbd_edpt_xfer(rhport, usbtmc_state.ep_bulk_in, usbtmc_state.ep_bulk_in_buf, (uint16_t)packetLen) );
-        if(((packetLen % USBTMCD_MAX_PACKET_SIZE) != 0) || (packetLen == 0 ))
+        if(((packetLen % usbtmc_state.ep_bulk_in_wMaxPacketSize) != 0) || (packetLen == 0 ))
         {
           usbtmc_state.state = STATE_TX_SHORTED;
         }
@@ -680,7 +688,7 @@ bool usbtmcd_control_xfer_cb(uint8_t rhport, uint8_t stage, tusb_control_request
     usbtmc_state.transfer_size_remaining = 0u;
       // Check if we've queued a short packet
       criticalEnter();
-      usbtmc_state.state = ((usbtmc_state.transfer_size_sent % USBTMCD_MAX_PACKET_SIZE) == 0) ?
+      usbtmc_state.state = ((usbtmc_state.transfer_size_sent % usbtmc_state.ep_bulk_in_wMaxPacketSize) == 0) ?
               STATE_ABORTING_BULK_IN : STATE_ABORTING_BULK_IN_SHORTED;
       criticalLeave();
       if(usbtmc_state.transfer_size_sent  == 0)

src/class/usbtmc/usbtmc_device.h

@@ -35,10 +35,6 @@
 #define CFG_TUD_USBTMC_ENABLE_488 (1)
 #endif
 
-// USB spec says that full-speed must be 8,16,32, or 64.
-// However, this driver implementation requires it to be >=32
-#define USBTMCD_MAX_PACKET_SIZE (TUD_OPT_HIGH_SPEED ? 512 : 64)
-
 /***********************************************
  *  Functions to be implemeted by the class implementation
  */