Download Supporting Tcl in Hardware

Supporting Tcl in Hardware
Scott Thibault
Green Mountain Computing Systems
Embedded Systems Vision
X-Acute Development Platform
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VB alternative.
XML based language.
TCL program code.
Persistent storage.
Targets Palm OS,
Pocket PC, Linux …
 Used commercially.
Tcl on Board! Platform
 Hardware bytecode/
instruction set.
 Bytecode processor.
 Core TCL commands
in runtime library.
 TCP/IP/PPP stack in
runtime library.
Why TCL?
 High-level scripting language.
 No pointers.
 Automatic memory management.
 Straight forward network support.
 Powerful string processing.
 Easy to learn.
 Cross-platform support.
Why Hardware?
 Limited performance.
 Limited memory
(under 1MB).
Implementation Issues
 Object representation (dual-port objects).
 Dynamic typing.
 List implementation.
 Memory management.
loadScalar1
3
pushInt
pushImm1
1
sub
assignScalarInt1 -3
Systems Programming
All-TCL Platform
 OS (trap handlers, etc.)
 Interrupt handlers.
 Device drivers.
 Buffers.
 Efficient arrays.
 Efficient records.
Protocol Stack Example
proc ppp_dispatch {} {
global ppp_buffer, ppp_end, ppp_lcp_open, ppp_reject_id, ppp_receiving, ppp_reject
set proto [sread_word_big $ppp_buffer 2]
if {$proto == 49185} {
ppp_handle_lcp
} elseif {$proto == 32801} {
ppp_handle_ipcp
} elseif {$proto == 33} {
set ip_packet [ip_process 4 [expr $ppp_end - 6] $ppp_buffer]
} elseif {$ppp_lcp_open} {
sshift ppp_buffer 4 6 [expr $ppp_end - 4]
set ppp_end [expr $ppp_end + 6]
swrite_word_big ppp_buffer 2 -16351
swrite ppp_buffer 4 8
swrite ppp_buffer 5 $ppp_reject_id
incr ppp_reject
swrite_word_big ppp_buffer 6 [expr $ppp_end - 4]
swrite_word_big ppp_buffer 8 $proto
ppp_transmit $ppp_end 1
}
set ppp_end 0
set ppp_receiving 0
if {$proto == 33} {ppp_ip_send $ip_packet}
}
Prototype Implementation
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FPGA implementation.
32k logic gates.
5 MHz (up to 36MHz).
3.5 cycles/instruction.
128k address space.
16 bit bus.
48 bit objects.
Example Web Server
 Embedded HTTP server.
 Hypothetical climate-control device.
 PPP over 9600 baud RS232 connection.
 5.25 seconds/request (4.71 seconds I/O).
 ROM image 32k bytes.
Conclusions
 TCL beneficial to embedded systems
programming.
 Demonstrated TCL in system code.
 Hardware implementation feasible.
 Small memory footprint.