Changes between Version 37 and Version 38 of io_operations

Timestamp:

Jan 16, 2018, 6:16:16 PM (7 years ago)

Author:

alain

Comment:

--

io_operations

@@ -93 +93 @@
 The ''device'' argument is the extended pointer on the device descriptor.
 
-== F) I/O operation ==
+== F) Global I/O operation scenario  ==
 
-The I/O operation mechanism involves generally three clusters : client cluster / server cluster / IO cluster. It does not use any RPC: 
+The I/O operation mechanism involves generally three clusters : client cluster / server cluster / IO cluster. It does not use any RPC, but uses only remote accesses to to execute the three steps implied by any I/O operation:
  * To post a new command in the waiting queue of a given (remote) device descriptor, the client thread uses only few remote accesses to be registered in the distributed XLIST rooted in the server cluster.
  * To launch the I/O operation on the (remote) peripheral, the server thread uses only remote accesses to the physical registers located in the I/O cluster.
@@ -140 +140 @@
 To reduce various synchronisation mechanisms, ALMOS-MKH uses IPIs (Inter Processor Interrupt) : Any kernel instance, running on any corein any cluster can send an IPI to any other core in the architecture, using a remote write access to the relevant register in the PIC infrastructure. An IPI is handled as a special interrupt by the target core, and simply forces a scheduling on the target core. 
 
-== H) Implementations ==
+== H) Text terminals ==
+
+The target hardware architectures generally provide a variable - but bounded - number of text terminals (called TXT channels). This NB_TXT_CHANNELS is an hardware parameter defined in the ''arch_info.bin file. We describe here how ALMOS-MKH uses these resources:
+ 1. The TXT[0] terminal is reserved for the kernel. It is normally used by the kernel to display log and/or debug messages. It can only be used by the user processes for debug, through some specific system calls such as the panic() or display_xxx() functions, that should not be used in normal exploitation.
+ 1. The other (NB_TXT_CHANNELS - 1) terminals TXT[i] are shared resources used by all user processes. During kernel initialization,  ALMOS-MKH creates the first ''INIT'' user process, that creates itself (NB_TXT_CHANNELS -1) ''KSH'' user processes (one shell per user text terminal). All user process created by the KSH[i] process
+share the same TXT[i] terminal, and belong to the same ''group'' of process.  
+ 1. In normal use, the ''KSH[i]'' processes should not be destroyed. If a ''KSH[i]'' process is killed, it is automatically recreated by the ''INIT'' process, to guaranty that there is always one ''KSH[i]'' for each TXT_i terminal.
+ 1. Regarding the WRITE accesses, all processes attached to the same TXT[i] terminal can atomically display character strings without any guaranty on the order.mutual exclusion mechanism. The strings providing from various processes will be simply sequentialized
+by the kernel thread associated to the shared TXT[i] device.
+ 1. Regarding the READ accesses, only one process the group of process attached to the TXT[i] terminal (called  ''foreground'' process) can read characters. The other processes (called s ''background'' processes) should not try to read characters. If a background process try to read, it receives a SIGSTOP signal, and will keep blocked
+until the user uses the fg shell command to put it in foreground mode. 
+ 
+== I) Implementations ==
 
 === 1. TSAR_MIPS32 architecture ===