Abstract:
A microcontroller includes a general purpose input/output (GPIO) port having a plurality of bits coupled to a plurality of external pins; a first set of registers for providing at least one of first control and data input/output functionality of the GPIO port; a second set of registers for providing at least one of second control and data input/output functionality of the GPIO port; and a multiplexer and associated select register for controlling the multiplexer to control said GPIO port through either said first or second register set.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. Provisional Patent Application Ser. No. 61/539,703 filed Sep. 27, 2011, titled “VIRTUAL GENERAL PURPOSE INPUT/OUTPUT FOR A MICROCONTROLLER,” which is hereby incorporated by reference in its entirety as if fully set forth herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Technical Field 
         [0003]    The present disclosure relates to microcontrollers and, in particular, to general purpose input/output ports in microcontrollers. 
         [0004]    2. Description of the Related Art 
         [0005]    A general purpose input/output (GPIO) port is generally understood as a parallel digital input/output port of a microcontroller. With current microcontrollers, GPIO functions are organized by ports (A, B, C, etc.), with each port having a set of registers input/output registers to control it. Furthermore, to control whether the port is used for digital input or digital output, a direction register such as a tri-state control register can be provided. Increasingly, microcontrollers are “low pin count” devices. 
         [0006]    When, as a consequence, a large number of peripherals are multiplexed onto each pin, it is unlikely that more than one to three GPIO functions will be available on any given port, once a user allocates the pins necessary for dedicated pin functions, such as UART (universal asynchronous receiver/transmitter), SPI (serial peripheral interface), I2C (Inter-integrated circuit), etc. This means that when the user wants a coherent (atomic, i.e., the ability to read or write the set of GPIO pins with a single CPU instruction) set of GPIO pins with more than a couple of pins, they must access multiple registers to drive data out on or sample data from those pins. This leads to limitations, such as the inability to drive all GPIO pins high at the same time, or to sample all GPIO pins at the same time. 
       SUMMARY 
       [0007]    These and other drawbacks in the prior art are overcome in large part by a system and method according to embodiments of the present invention. 
         [0008]    A microcontroller according to embodiments includes a general purpose input/output (GPIO) port having a plurality of bits coupled to a plurality of external pins; a first set of registers for providing at least one of first control and data input/output functionality of the GPIO port; a second set of registers for providing at least one of second control and data input/output functionality of the GPIO port; and a multiplexer and associated select register for controlling the multiplexer to control said GPIO port through either said first or second register set. 
         [0009]    In some embodiments, the first and second register set comprise a read register, a write register, and a direction control register. In some embodiments, the port comprises a controllable output driver having an output coupled with an external pin and an input driver having an input coupled with the external pin. In some embodiments, the first and second read register are coupled through a first multiplexer with the output of the input driver, the first and second write register are coupled through a second multiplexer with the input of the output driver, and the first and second direction control register are coupled through a third multiplexer with a control input of the output driver. In some embodiments, the microprocessor further includes a peripheral pin select unit operable to programmably assign an external pin to the second functionality of the GPIO. 
         [0010]    An input/output configuration for a processor according to some embodiments include a first plurality of registers comprising a first general purpose input/output configuration selectively coupled to an external pin of the processor; a second plurality of registers comprising a second general purpose input/output configuration selectively coupled to the external pin; and a control register operably coupled to control switching between the first general purpose input/output configuration and the second general purpose input/output configuration. In some embodiments, the input/output configuration includes at least one multiplexer for receiving control inputs from the control register for selecting between the first general purpose input/output configuration and the second general purpose input/output configuration. In some embodiments, the first plurality of registers includes a first read register, a first write register, and a first direction control register; and the second plurality of registers includes a second read register, a second write register, and a second direction control register. In some embodiments, the at least one multiplexer includes a first multiplexer for selecting between the first direction control register and the second direction control register; and a second multiplexer for selecting between the first write register and the second write register. In some embodiments, the input/output configuration includes a controllable output driver having an output coupled with the external pin and an input driver having an input coupled with the external pin. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The present invention may be better understood, and its numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings. The use of the same reference symbols in different drawings indicates similar or identical items. 
           [0012]      FIG. 1  is a diagram illustrating an exemplary microcontroller pin configuration. 
           [0013]      FIG. 2  is a diagram illustrating a conventional GPIO port. 
           [0014]      FIG. 3  is a diagram illustrating a GPIO port in accordance with embodiments of the invention. 
           [0015]      FIG. 4  is a diagram illustrating a GPIO port in accordance with embodiments of the invention. 
           [0016]      FIG. 5  illustrates exemplary registers for use with a virtual port in accordance with embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    The disclosure and various features and advantageous details thereof are explained more fully with reference to the exemplary, and therefore non-limiting, embodiments illustrated in the accompanying drawings and detailed in the following description. Descriptions of known programming techniques, computer software, hardware, operating platforms and protocols may be omitted so as not to unnecessarily obscure the disclosure in detail. It should be understood, however, that the detailed description and the specific examples, while indicating the preferred embodiments, are given by way of illustration only and not by way of limitation. Various substitutions, modifications, additions and/or rearrangements within the spirit and/or scope of the underlying inventive concept will become apparent to those skilled in the art from this disclosure. 
         [0018]    As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having,” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, product, article, or apparatus that comprises a list of elements is not necessarily limited only those elements but may include other elements not expressly listed or inherent to such process, process, article, or apparatus. Further, unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present). 
         [0019]    Additionally, any examples or illustrations given herein are not to be regarded in any way as restrictions on, limits to, or express definitions of, any term or terms with which they are utilized. Instead these examples or illustrations are to be regarded as being described with respect to one particular embodiment and as illustrative only. Those of ordinary skill in the art will appreciate that any term or terms with which these examples or illustrations are utilized encompass other embodiments as well as implementations and adaptations thereof which may or may not be given therewith or elsewhere in the specification and all such embodiments are intended to be included within the scope of that term or terms. Language designating such non-limiting examples and illustrations includes, but is not limited to: “for example,” “for instance,” “e.g.,” “in one embodiment,” and the like. 
         [0020]    As will be explained in greater detail below, according to various embodiments, a user can map GPIO pins that are spread across multiple physical ports to a single software port, called a Virtual Port. That is, in some embodiments, a Virtual Port is constructed by mapping unrelated pins to a single “port.” 
         [0021]    In some embodiments, the mapping employs a remappable pin function, such as the Peripheral Pin Select (PPS) infrastructure, available from Microchip, which provides flexible multiplexing between pins and peripherals, and also employs a dedicated set of extra GPIO registers. It then becomes possible to simultaneously drive or sample multiple GPIOs even though they do not necessarily belong to the same originally assigned port. In other applications, the same port may be used in different configurations that require extensive re-programming of that port. According to an embodiment, at least a second set of registers allows users to set two or more configurations of a GPIO port which can be switched by simply setting at least one bit of a select register. 
         [0022]    Turning now to the drawings and, with particular attention to  FIG. 1 , a diagram of an exemplary microcontroller that can be used in accordance with the teachings of the disclosure is shown. The microcontroller  100  may be embodied as a PIC18F67J94, available from Microchip Technologies, Inc., or a similar microcontroller or processor. Microcontroller  100  includes a plurality of pins, many of which are used to implement more than one function. In the example illustrated, pins with the designation “R” are remappable using a Peripheral Pin Select functions. Peripheral Pin Select allows a programmer to map the I/O of most peripherals to a selection of pins. 
         [0023]    However, with low pin counts and increasing number of peripherals, users are often constrained in their GPIO to “leftover” pins. Even with PPS (Peripheral Pin Select), board layout may constrain pin selection on a device. If a multi-pin GPIO “port” is required to implement a protocol or control, and all of the pins are not on the same physical port (i.e.—Port A, B, etc.), then multiple instruction cycles are required to read the port, for example with a read register (PORT), write the port, for example with a write register (LAT), or switch directionality of the port, for example with a tri-state register (TRIS) on these pins. With conventional systems, it is impossible to keep cycle coherency on the GPIO port for reads and writes. 
         [0024]    For example, shown in  FIG. 2  is a conventional GPIO port  200 . Shown is I/O pin  201 , read driver  204  and read register  210  (PORT); and tri-state write driver  202 , with a write register (LAT)  208  and select register  206  (TRIS). In operation, the register  206  is used to select the input or output functioning or directionality of the port  200 . 
         [0025]    According to an embodiment, a virtual port allows a user to allocate any possible GPIO pin to a virtual PORT. As shown in  FIG. 3 , an existing GPIO port is assigned a shadow function which can be activated by merely setting a single bit switching the functionality from an original configured port to the configuration set in the register assigned to the virtual function. 
         [0026]    More particularly,  FIG. 3  illustrates an exemplary GPIO virtual port structure according to an embodiment. As shown, the port  300  includes pin  301 , drivers  302 ,  304 , and read (PORT) register  210 , write (LAT) register  208 , and select (TRIS) register  206 , which function similarly to conventional ports. However, according to embodiments, the virtual port  300  includes virtual write (PBLAT) register  306 , virtual read (PBPORT) register  310 , and virtual select (TRIS) register  308 . Multiplexers  314 ,  316  allow users to select between the “real” or virtual port functions. More particularly, in standard operation, the standard port configuration may be used. By selecting using the virtual pin select line(s)  318 ,  313 ,  320 , a user can select the virtual port function. 
         [0027]    The additional logic requires only a minimum of real estate, thus, die cost is kept small. For example, with 40 GPIO pins and 8-pin virtual port, the additional logic requires about 1K gates. However, this requirement can be even further reduced when using an existing PPS. 
         [0028]    Generally, the GPIO is considered as a dedicated pin function, and not treated as a peripheral. However, according to various embodiments, the GPIO is treated like any other mappable peripheral. As will be discussed in greater detail below, according to some embodiments, using a remappable pin function infrastructure, such as the PPS infrastructure, which allows for multiplexing between any or almost any pin and any or almost any peripheral, a new “GPIO peripheral” is added to the list of re-mappable peripherals. That is, with a remappable pin function such as PPS, the virtual port looks just like another peripheral device. Within this GPIO peripheral, a new set of dedicated GPIO registers functions identically to pin-based GPIO functions. In some embodiments, this additional GPIO peripheral can be placed as the lowest priority re-mappable peripheral, right above the pin-based GPIO pin functions (which are not part of the re-mappable pin function set), thereby making them behave like the pin-based GPIO pin functions (look and feel), but independent of the physical pin they are mapped to. Consequently, a group of disjointed (i.e.—spread across multiple GPIO “ports”) pins can be transformed into what looks like an atomic (i.e.—all on the same GPIO “port”) group of pins with minimal additional logic. 
         [0029]    Turning now to  FIG. 4 , a diagram  400  showing virtual GPIO in a remappable pin function environment is shown. The environment  400  includes GPIO virtual port structure  402  and peripherals  422   a - 422   n.  The GPIO virtual port structure includes pin  401 , drivers  302 ,  304 , and read (PORT) register  210 , write (LAT) register  208 , and select (TRIS) register  206 , which function similarly to conventional ports and as described above with reference to  FIG. 3 . In addition, the virtual port  402  includes virtual write (PBLAT) register  306 , virtual read (PBPORT) register  310 , and virtual select (TRIS) register  308 . Multiplexers  414 ,  416  allow users to select between the “real” or virtual port functions in a manner similar to that discussed above. By selecting the virtual pin select line(s) (not shown), a user can select the virtual port function. 
         [0030]    In addition, in a remappable pin function environment, the multiplexers  414 ,  416  receive inputs from peripherals  422   a,    422   n.  In particular, in some embodiments, the output enable lines  426   a,    426   n  are provided to multiplexer  414  to enable writing to the pin  401 , and output data lines  428   a  . . .  428   n  are provided to multiplexer  416  to write data to the pin. 
         [0031]    According to various embodiments, a set of separate PBLAT, PBPORT and PBTRIS registers is implemented. For example, shown in  FIG. 5  are 8-bit wide LAT (write)  308 , port (read)  310 , and tris (select)  306  registers for a PIC18 microcontroller. Register width would be the native data width of the architecture, so that register reads/writes are atomic. 
         [0032]    Although the foregoing specification describes specific embodiments, numerous changes in the details of the embodiments disclosed herein and additional embodiments will be apparent to, and may be made by, persons of ordinary skill in the art having reference to this description. In this context, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of this disclosure. Accordingly, the scope of the present disclosure should be determined by the following claims and their legal equivalents.