Changeset 539 for trunk/hal/tsar_mips32

Timestamp:

Sep 21, 2018, 10:21:42 PM (6 years ago)

Author:

nicolas.van.phan@…

Message:

TTY MUX 4 : Multiplex TTY character sending

Now, when a thread wants to write to a tty,
when the dev_txt_write() or dev_txt_sync_write() are called,
they all call soclib_mtty_aux() with a channel number.
The soclib_mtty_aux() function will write the string char by char,
with each char preceded by the channel number, so that the receiving end
knows to which tty a character is addressed to.

N.B. dev_txt_write() makes *synchronous* writes for the moment
because unlike the vci_tty_tsar, the vci_multi_tty doesn't raise
interrupt except when a new char is received, so we can't use the
interrupt mechanism for writes.

N.B. Now, the TTY DEV threads all write to the same register (WRITE),
but when a thread sends a 2-byte (tty dest. nb. + char), the two must be
send consecutively, without another thread sending a byte in between.
Consequently, a lock has been added to guarantee this atomicity.

File:

• trunk/hal/tsar_mips32/drivers/soclib_mtty.c (modified) (4 diffs)

trunk/hal/tsar_mips32/drivers/soclib_mtty.c

@@ -48 +48 @@
 #endif
 
+extern   chdev_directory_t    chdev_dir;  // allocated in the kernel_init.c file.
+extern   spinlock_t           txt0_lock;  // Initialized in kernel_init.c
 ////////////////////////////////////////////////////////////////////////////////////
 // These global variables implement the MTTY_RX  FIFOs (one per channel)
@@ -538 +540 @@
     char     * buffer = ((txt_sync_args_t *)args)->buffer;
     uint32_t   count  = ((txt_sync_args_t *)args)->count;
+    uint32_t   channel = ((txt_sync_args_t *)args)->channel;
     
     // get TXT0 chdev cluster and local pointer
@@ -554 +557 @@
     xptr_t status_xp = XPTR( tty_cxy , tty_ptr + MTTY_STATUS );
 
+    reg_t  save_sr;
+
     // loop on characters (busy waiting policy)
     for( i = 0 ; i < count ; i++ )
     {
+        // This is the MTTY multiplexing
+        // Before each character, we send the destination TTY number for this char.
+        // The two bytes (dest number + char) must be sent consecutively,
+        // so to guarantee this atomicity, we use a lock to prevent other
+        // concurrent server DEV threads to write a byte in between our two bytes
+
+        // Get the lock
+        spinlock_lock_busy( &txt0_lock, &save_sr );
+
+        // Send the destination TTY number
         do
         {
@@ -564 +579 @@
 
             // transfer one byte if TX buffer empty
+            if ( empty )  hal_remote_sb( write_xp , channel + '0' );
+            
+        }
+        while ( empty == false );
+
+        // Send the character
+        do
+        {
+            // get MTTY_STATUS
+            status = hal_remote_lw( status_xp );
+            empty  = ( (status & MTTY_STATUS_TX_FULL) == 0 );
+
+            // transfer one byte if TX buffer empty
             if ( empty )  hal_remote_sb( write_xp , buffer[i] );
         }
         while ( empty == false );
+
+        // Release the lock
+        spinlock_unlock_busy( &txt0_lock, save_sr );
     }
 }  // end soclib_mtty_aux()