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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The field of the invention is that of electronic integrated circuits.
2. Description of the Prior Art
To be more precise, the invention concerns a microcontroller integrated
circuit. A microcontroller is usually a VLSI (Very Large Scale
integration) integrated circuit containing all or most of the components
of a "computer". Its function is not predefined but depends on the program
that it executes, with the result that in respect of potential
applications it is very much a general purpose device.
A microcontroller necessarily comprises a processor core including a
command sequencer (which is a device distributing various control signals
to the other components according to the instructions of a program), an
arithmetic and logic unit (for processing the data) and registers (which
are specialized memory units).
The other components of the "computer" can be either internal or external
to the microcontroller, however. In other words, the other components are
integrated into either the microcontroller or auxiliary circuits.
These other components of the "computer" are data processing and/or storage
devices, for example read only or random access memory containing the
program to be executed, clocks and interfaces (serial or parallel).
As a general rule, a system based on a microcontroller therefore comprises
a microchip containing the microcontroller, and a plurality of microchips
containing the external data processing and/or storage devices which are
not integrated into the microcontroller. A microcontroller-based system of
this kind comprises, for example, one or more printed circuit boards on
which the microcontroller and the other components are mounted.
It is the application program, i.e. the program which is executed by the
microcontroller, which determines the overall operation of the
microcontroller system. Each application program is therefore specific to
a separate application.
In most current applications the application program is too large to be
held in the microcontroller and is therefore stored in a memory external
to the microcontroller. This program memory, which has only to be read,
not written, is generally a reprogrammable read only memory (REPROM).
After the application program has been programmed in memory and then
started in order to be executed by the microcontroller, the
microcontroller system may not function as expected.
In the least unfavorable situation this is a minor dysfunction of the
system and the microcontroller is still able to dialog with a test station
via a serial or parallel interface. This test station is then able to
determine the nature of the problem and indicate precisely the type of
correction (software and/or physical) to be applied to the system for it
to operate correctly.
Unfortunately, most dysfunctions of a microcontroller-based system result
in a total system lock-up, preventing any dialog with a test station. It
is then impossible to determine the type of fault, i.e. whether it is a
physical fault (in the microcontroller itself, in an external read only
memory, in a peripheral device, on a bus, etc) or a software fault (i.e.
an error in the application program). The troubleshooting technique
usually employed in these cases of total lock-up is based on the use of
sophisticated test devices requiring the application of probes to the pins
of the various integrated circuits of the microcontroller-based system
under test.
There are various problems associated with the use of such test devices for
troubleshooting a microcontroller-based system. The probes used in these
test devices are very fragile, difficult to apply because of the small
size of the circuit and their close packing, and may not make good contact
with the circuit.
Also, because of their high cost, these test devices are not mass produced.
Consequently, faulty microcontroller-based systems cannot be repaired
immediately, wherever they happen to be located at the time, but must
first be returned to a place where a test device is available.
Troubleshooting a microcontroller-based system in this way is
time-consuming, irksome and costly.
To avoid the need for direct action on the microcontroller-based system
each time the application program executed by the microcontroller of the
system is changed, it is standard practise to use a downloadable read only
memory to store the application program, a loading program being written
into a mask-programmed read only memory of the microcontroller. The
mask-programmed read only memory of the microcontroller is integrated into
the microcontroller and programmed once and for all during manufacture of
the microcontroller.
To change the application program the microcontroller is reset by running
the downloading program. This downloading program can then communicate
with a workstation connected to the microcontroller by an appropriate
transmission line, this workstation containing the new application program
to be written into the microcontroller. The downloading program receives
the new application program and loads it into a read only memory external
to the microcontroller.
Although this solution avoids the need for direct action on the
microcontroller-based system (which would entail removing from the system
the reprogrammable read only memories containing the application program,
writing into these memories the new application program using an
appropriate programming device and then replacing them in the system), it
nevertheless has a major drawback, namely specialization of the
microcontroller during manufacture.
Each type of reprogrammable memory is associated with a different
downloading program because the programming parameters (voltage to be
applied, duration for which the voltage is to be applied, etc) vary with
the technology employed. The downloading program is written once and for
all into the mask-programmed internal memory of the microcontroller and
the latter is therefore restricted to using memory components of the type
for which this downloading program was written. In other words, the
microcontroller is not a standard component and this increases its cost of
manufacture.
One object of the invention is to overcome these various drawbacks of the
prior art.
To be more precise, an object of the invention is to provide a
microcontroller circuit which can verify quickly, simply, reliably and at
low cost the operation of a system based on the microcontroller.
Another object of the invention is to provide a microcontroller integrated
circuit which can accurately locate the defective component or components
of a system using the microcontroller in the event of dysfunction of the
system.
A further object of the invention is to provide a microcontroller
integrated circuit which avoids the need for direct action on the
microcontroller-based system to change the application program, whilst
remaining standard as regards the type of memory component with which it
can be used in a system.
SUMMARY OF THE INVENTION
These objects, and others that emerge below, are achieved in accordance
with the invention by means of a microcontroller integrated circuit
comprising a processor core adapted to exchange data with at least one
data processing and/or storage device, said integrated circuit comprising
a read only memory containing a generic program such as a test program
which can be executed by said microcontroller, said generic program
including a basic function for writing data into said data processing
and/or storage device or devices and said write function being used to
load a downloading program.
The storage and/or data processing devices are either integrated into the
microcontroller (i.e. into the microcontroller integrated circuit
comprising the processor core) or external to the microcontroller and
integrated into separate circuits.
In a preferred embodiment of the invention said read only memory containing
the generic program is a mask programmed read only memory, said
mask-programmed read only memory being programmed once and for all during
manufacture of said integrated circuit.
Thus, unlike prior art microcontrollers in which the mask-programmed read
only memory, if any, contains either an application program (if this is
small) or a downloading program (restricted to a specific type of memory
component), the microcontroller of the invention has a mask-programmed
memory containing a generic program such as a test program.
Accordingly, the microcontroller can be tested with its environment,
independently of the application program. This test can be run either
before the application program is started or after the application is
started if the system in which the microcontroller is used fails or is
subject to a dysfunction.
In a preferred embodiment of the invention said generic program such as a
test program comprises a selection of the following basic functions:
reading of data stored by said data processing and/or storage device or
devices;
writing of data in said data processing and/or storage device or devices;
executing a program written in said data processing and/or storage device
or devices.
The generic program such as a test program can therefore be very small in
size and thus readily integrated into the microcontroller.
These three basic functions provide for complete testing of the
microcontroller alone or with its environment.
Said data processing and/or storage device or devices are advantageously
selected from the group including:
reprogrammable read only memories, programmable more than once after
fabrication of said integrated circuit;
random access memories;
clocks;
peripheral devices.
The read function is used to verify the content of the read only memory
storing (or for storing) the application program, to test the information
acquired by the various peripheral devices and, in combination with the
write function, to test the validity of the random access memory.
The write function, which advantageously does not use any random access
memory, is used to validate the various peripheral devices and the random
access memory. It can load any program into the random access memory,
including a more powerful self-test program (after verifying that the
microcontroller and its environment are capable of executing the basic
functions correctly), or any program for downloading the read only memory
enabling dynamic adaptation of the microcontroller-based system by
modification of its application program. The fact that any downloading
program can be written into random access memory is very important because
this means that the microcontroller of the invention is not restricted to
a specific type of memory component: the microcontroller of the invention
is a standard and therefore low cost product.
The execute function is used to execute a program written in random access
memory by the write function.
The set of three functions can be used to carry out all kinds of tests and
even for troubleshooting during production.
The integrated circuit of the invention advantageously comprises
communication means implementing a protocol for dialog between a generic
test program and a test station connected to said integrated circuit.
The microcontroller-based system can therefore be remotely tested from the
test station, the generic test program supplying to the test station, on
request, full information concerning the microcontroller and its
environment.
The group of basic functions constituting said generic test program
preferably includes measurement of the speed at which data is transmitted
from said test station so that said communication means can match the
speed at which data is transmitted from said integrated circuit to said
speed at which data is transmitted by said test station. This simplifies
the test station because it always transmits data at the same speed,
regardless of the speed at which the microcontroller to which it is
connected operates.
Said communication means are advantageously equivalent to a universal
asynchronous receiver/transmitter (UART; conventionally incorporated in a
microcontroller) of which only the receive and transmit signals are used.
Said communication means preferably comprise a serial interface and said
generic test program receives from said test station messages for
activating either one of said basic functions or a pointer positioning
function and sends to said test station messages as to the result of
activating one of said elementary functions. The serial interface is an
RS232 interface, for example.
Said activation messages are advantageously selected from the group
comprising:
messages specifying a predetermined address for a current pointer, each
message comprising an address specification command word in which the
number of specification bytes is encoded and at least one data word
containing said specification bytes;
messages to read a memory from the current pointer address, each message
comprising a read command word in which a number of bytes to read is
encoded;
messages to write in a memory from the current pointer address, each
message comprising a write command word in which a number of bytes to
write is encoded and at least one data word containing said bytes to
write;
messages to execute a program stored in a memory from the current pointer
address, each message comprising an execute command word.
Each of said result messages advantageously comprise at least one data word
containing read data. In other words, the activation messages comprise a
command word, possibly followed by one or more data words, and the result
messages comprise one or more data words.
Each command word and each data word advantageously comprise at least one
start bit, at least one data bit and at least one stop bit. This secures
transmission of data between the generic test program of the
microcontroller and the test station.
Each of said command words preferably comprises eight data bits, as
follows:
two bits encoding the command word type; and
six bits encoding a number of specification bytes, bytes to read and bytes
to write, according to whether the command word coded in the other two
bits is respectively a specification command word, a read command word or
a write command word.
In an advantageous embodiment of the invention said integrated circuit
comprises a pin for starting said generic program such as a test program,
said generic program such as a test program being started when said start
pin is excited after said integrated circuit has been reset. The start pin
is used to tell the microcontroller that it must switch to test mode, i.e.
start execution of the generic test program.
The invention also concerns a method of manufacturing a microcontroller
integrated circuit comprising a step of etching a mask-programmed read
only memory containing said generic program such as a test program.
The invention also concerns an integrated circuit test station for testing
an integrated circuit of the invention, said station comprising means for
transmitting activation messages and receiving result messages. Other
features and advantages of the invention will emerge from a reading of the
following description of a preferred embodiment of the invention given by
way of non-limiting example only and from the appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a simplified block diagram of a system based on one embodiment
of a microcontroller of the invention, this microcontroller-based system
being connected to a test station.
FIG. 2 shows a simplified block diagram of one embodiment of a generic test
program as contained in the mask-programmed read only memory of a
microcontroller of the invention.
FIG. 3 shows one embodiment of the structure of a command word exchanged
between the test station and the microcontroller of the invention as shown
in FIG. 1.
FIG. 4 shows one embodiment of the structure of a data word exchanged
between the test station and the microcontroller of the invention as shown
in FIG. 1.
FIGS. 5 to 8 each show one example of dialog between the microcontroller of
the invention and the test station as shown in FIG. 1, in the following
respective cases:
* positioning a pointer;
* reading a memory;
* writing a memory;
* executing a program.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In this description said generic program is a generic test program, for
example, and said read only memory containing this generic program is a
mask-programmed memory programmed once and for all during manufacture of
said integrated circuit.
The invention thus concerns a microcontroller integrated circuit (referred
to simply as a microcontroller in the remainder of the description).
FIG. 1 shows one specific embodiment of a microcontroller 11 of the
invention and a system 12 based on the microcontroller 11.
In the specific embodiment the microcontroller 11 comprises a minimum of
components namely:
a processor core 13;
a mask-programmed read only memory 14, programmed once and for all during
manufacture of the microcontroller, and
a UART (universal asynchronous receiver/transmitter) 15.
The other data processing and/or storage devices enabling the
microcontroller 11 to operate are external to the microcontroller 11 in
this example, and with the latter constitute the microcontroller-based
system 12. In this specific embodiment the data processing and/or storage
devices are:
a reprogrammable read only memory (REPROM) 16 which can be programmed more
than once after manufacture of the microcontroller 11 and is for storing
the application program executed by the microcontroller 11 and defining
the function of the latter and more generally the function of the system
12 as a whole;
a random access memory (RAM) used during execution of a program by the
microcontroller 11;
a clock 18;
two peripheral devices 19, 110.
Clearly the microcontroller of the invention is not restricted to this
particular embodiment. Thus, in other embodiments, all or some of the data
processing and/or storage devices 16 through 110 can be integrated into
the microcontroller.
Likewise, other types of data processing and/or storage devices (either
internal or external to the microcontroller 11) can be used.
The mask-programmed read only memory of the microcontroller 11 contains a
generic test program.
In a preferred embodiment, a simplified block diagram of which is shown in
FIG. 2, the generic test program 21 comprises a plurality of basic
functions including:
22: reading of data stored in some data processing and/or storage devices,
such as the reprogrammable read only memory 16, the random access memory
17 or the peripheral devices 19, 110;
23: writing of data in some data processing and/or storage devices such as
the random access memory 17 or the peripheral devices 19, 110;
24: execution of the program written into one of the data processing and/or
storage devices such as the random access memory 17.
In this embodiment the generic test program 21 also comprises two other
basic functions, namely measurement of a transmission speed (25) and
positioning of a pointer (26). These functions are described in detail
below.
The generic test program 21 is used to verify and validate either the
microcontroller 11 alone or the microcontroller 11 and its environment
(i.e. the microcontroller-based system 12).
The generic test program 21 is used to test and validate each of the
components constituting the microcontroller-based system.
The correct operation of the microcontroller alone can be verified in a
first phase, i.e. before it is introduced into the system 12 in order to
cooperate with the data processing and/or storage devices 16 through 110.
The correct operation of the system 12 as seen by the microcontroller can
be verified in a second phase.
These two preliminary test and validation phases do not require the
presence of an application program in memory (read only memory 16 or
random access memory 17). All that is required is to tell the
microcontroller 11 that it must switch to test mode, in which mode it
executes the generic test program (as contrasted with the normal operating
mode in which it executes the application program contained in memory). In
one specific embodiment of the invention the microcontroller 11 comprises
a start pin (not shown) and the generic test program is started when this
start pin is excited after the microcontroller has been reset.
Note that the microcontroller 11 and its environment (external devices 16
through 110) can also be tested and validated in the event of a
dysfunction of the system 12 during execution of the application program.
Finally, the write basic function 23 can write into random access memory a
test (or self-test) program that is more complex than the generic test
program 21 but whose correct execution presupposes that the
microcontroller 11 and its environment are operational in respect of
execution of the basic functions 22 through 24.
The application program, i.e. the program executed by the microcontroller
11 and which confers its function on it, is usually written into a memory
after the microcontroller 11 and its environment have been tested and
validated.
The generic test program 21 of the microcontroller of the invention offers
various ways to store the application program in memory.
A first way is to store the application program directly in random access
memory 17 using the write basic function 23.
A second way, offering better performance because it is durable, consists
in storing the application program indirectly in read only memory 16 and
storing beforehand in random access memory 17 a program for downloading
this read only memory 16. Clearly any type of downloading program (and
thus any type of reprogrammable memory) can be used because the generic
test program writes it into the random access memory 17 like any other
program (in other words, the content of the program written is transparent
insofar as the write function 23 of the generic test program 21 is
concerned). The microcontroller 11 of the invention can therefore adapt
dynamically to its application context (through the facility for
downloading of the read only memory) whilst remaining a standard product
(in that there is no limitation as to any specific type of reprogrammable
memory).
Referring to FIG. 1, the microcontroller 11 is usually connected to a test
station 111, by an RS232 serial link, for example. To this end the
microcontroller and the test station each comprise communication means for
implementing a dialog protocol. The test station 111 is a microcomputer,
for example.
In the specific embodiment of the invention shown in FIGS. 1 and 2 the
generic test program 21 comprises a basic function 25 for measuring the
transmission speed from the test station 111. The transmission speed of
the communication means 15 of the microcontroller 11 is then made equal to
that of the test station 111, and is therefore independent of the clock 18
of the system 12. The communication means 15 are equivalent to a UART
(Universal Asynchronous Receiver/Transmitter), for example, of which only
the receive signal Rx and transmit signal Tx are used.
One example of a protocol for exchange of data between the microcontroller
11 and the test station 111 is now described with reference to FIGS. 3
through 8.
The test station 111 sends to the microcontroller 11 messages to activate
one of the following four basic functions: read 22, write 23, execute 24
and position a pointer 26 of the generic test program 21.
In return, the generic test program 21 sends the test station 111 messages
as to the result of activating one of said basic functions.
An activation message comprises a command word, possibly followed by one or
more data words. A result message comprises one or more data words.
FIG. 3 shows one embodiment of the structure of a command word. In this
example a command word comprises a start bit D, a data byte 31 comprising
six bits N1 through N6 encoding the command word type and two stop bits
S1, S2.
The codes for the command word type are as follows:
00: position pointer command 26;
01: read command 22;
10: write command 23;
11: execute command 24.
FIG. 4 shows one embodiment of the structure of a data word. In this
example a data word comprises a start bit D, a data byte 41 and two stop
bits S1, S2.
The number coded in binary in bits N1 through N6 is one less than the
number of bytes to be coded (N) (i.e. N-1).
The number N to be coded is:
a number of bytes in which is specified the address at which a current
pointer must be positioned in the case of a pointer positioning command
word;
a number of bytes to be read from the current pointer address in the case
of a read command word;
a number of bytes to be written from the current pointer address in the
case of a write command word.
Each of FIGS. 5 through 8 shows one example of dialog between the
microcontroller of the invention and the test station. To simplify the
diagrams only the data bytes are shown (the start bits D and the stop bits
S1, S2 do not convey any data).
FIG. 5 shows the situation of specification by the test station of an
address to which the current pointer of the microcontroller is to be
positioned, the address specified being the memory address from which one
of the three basic functions (read, write, execute) is to be executed.
In this example the address specified is 123456 and each digit specifying
the address is coded on four bits.
Accordingly the test station first sends a command word S1 indicating that
this is a pointer positioning command (C2C1=00) and that the address is
coded on N=3 bytes (N6 to N1=(10) binary=2=N-1), followed by three data
words 52 through 54 containing the address (0001, 0010, 0011, 0100, 0101
and 0110 respectively corresponding to the coding of 1,2,3,4,5 and 6).
FIG. 6 shows the situation in which the test station commands reading of
bytes by the microcontroller from the current pointer address.
In this example the station sends a command word 61 indicating a read
(C2C1=01) and that there are N=4 (N6 to N1=(11) binary=3=N-1) bytes to
read. The microcontroller then sends the test station the four data words
62 through 65 containing the data read (bits denoted x to indicate any
value).
FIG. 7 shows the situation of the test station commanding writing of bytes
by the microcontroller from the current pointer address.
In this example the test station first sends a command word 71 indicating a
write (C2C1=10) and that there are N=5 (N6 to N1=(100) binary=4=N-1) bytes
to write, followed by five data words 72 through 76 containing the data to
be written (0 for all the bits in this example).
FIG. 8 shows the situation of the test station commanding execution by the
microcontroller of a program stored from the current pointer address.
Accordingly, the test station sends a command word 81 indicating execution
(C2C1=11).
The invention also concerns a method of manufacturing a microcontroller
integrated circuit as described above by means of one specific embodiment.
This method comprises a step of etching the mask-programmed read only
memory containing the generic test program.
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