Patent Application
20050038987
1. Field of the Invention
The present invention is related to chip that has power-up strapping functionality and that can temporarily change a state or mode of the chip.
2. Background Art
Products are manufactured that include chips having a plurality of selectable functions. The selectable functions use devices that can perform different functions allows the chips to be used in a variety of different systems. In order to properly set the function of the device, a mode or state is usually selected for the device based on the product it is incorporated within. The mode or state can be selected using a strapping system (e.g., mode or state setting system) in a variety of ways, including using: a dedicated pin, a register control block controlled by software running in the product, or the like. Thus, because a designer knows what product is being made, when the chip is inserted into the product a function of the device can be set using a signal that designates a mode or state. Using a strapping system may be favored because it does not require using a dedicated pin. Pins are in limited supply on a chip, and avoiding having to use one to set a mode of the device is desired.
In an example strapping system, an input/output (I/O) device on the chip is controlled through an enable signal. When the output is not enabled, the input floats. When the input floats, the input can be coupled to a resistive element to provide a strapping signal. The resistive element can be pulled-up (i.e., producing a HIGH strapping signal) or pulled-down (i.e., producing a LOW strapping signal). The strapping signal can be stored in a latch device or a flip-flop. During a reset operation, the latch can store the strapping signal. After the reset operation, the latch can close and the strapping signal can be substantially permanently stored. Then, a control device can use the strapping signal to set a substantially permanent mode or state of a device on the chip.
However, systems are increasingly requiring more flexibility during operation. For example, a system may need to temporarily switch modes of the device during a specified time period of operation to change the function of the device for that time period. Conventional systems using the various mode or state setting techniques cannot change the mode or state during operation (i.e., they cannot override the strapping value once it's been stored).
Therefore, what is needed is system than can change a mode or state of a device during operation.
Embodiments of the present invention provide systems and methods for strapping with override capability. A strapping system transmits a signal to the control system that is used to place the device in a first state (or mode) (e.g., client or master). An override system transmits a signal to the control system that is used to place the device in a second state (or mode) (e.g., client or master). The second state can be a temporary state.
Further embodiments, features, and advantages of the present inventions, as well as the structure and operation of the various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.
The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention.
The present invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers may indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number may identify the drawing in which the reference number first appears.
Overview
While specific configurations and arrangements are discussed, it should be understood that this is done for illustrative purposes only. A person skilled in the pertinent art will recognize that other configurations and arrangements can be used without departing from the spirit and scope of the present invention. It will be apparent to a person skilled in the pertinent art that this invention can also be employed in a variety of other applications.
Embodiments of the present invention provide a system and method that allow for overriding of a strapping signal. A strapping signal places a device (e.g., a processor) in first state or mode (e.g., client or master). An override system can be used to place the device in a second state or mode. The second state or mode can be temporary. The changing of the state or mode of the device may be needed to perform testing of the chip, during which a memory is written to and read from to verify operation of the chip. The changing of the state or mode of the device may also allow the device to perform alternative functions that are not available during its first state or mode.
For example, a product may have chip including a processor. The processor may be a client processor during a first state mode. If designated a client, the processor needs to stay a client so that it does not erroneously start performing master functions. However, the product may need the processor to perform master functions during a specified time period. This can be accomplished by overriding the strapping system with a signal, for example, from software. The software signal can override the strapping signal for a temporary period of time, allowing the processor to become a master. Once the processor has performed the master functions, the override signal ends and the processor returns to being a client.
One example product this system can be used in is Television-On-A-Chip technology.
Overall System
If signal 210 is from resistor 204 (e.g., a pull-up signal) the signal is a HIGH value. The HIGH value is then stored in latch 208.
If signal 210 is from resistor 206 (e.g., a pull-down signal) the signal is a LOW value. The LOW value is then stored in latch 208.
Signal 210 stored in latch 208 becomes the strapping signal that is used by controller 108 to place device 102 into a first or second state or mode (e.g., client or master). Although two resistors 204 and 206 are shown, only one resistor can be present depending on whether a pull-up or pull-down signal is desired.
In one example of
Strapping system 106 a resistive device 332, which is a pull-up resistive device in this embodiment. However, it is to be appreciated that a pull-down resistive device could also be used based on the application of the chip, as would be known to a skilled artisan.
Control system 108 includes multiplexers 330 and 340 and an OR gate 342. Multiplexer 330 receives strapping signal 378 and a SW_CPU_RESET signal 380 at its inputs and a signal 362 (see discussion of override system 110 below) at its control terminal. SW_CPU_RESET 380 is generated from a register (not shown) outside of system 100 that can be written by software. For example, SW_CPU_RESET signal 380 can be one or more bits in 32-bit or similar register in the product. So, basically, once the override has been activated, the O_CPU_RESET signal 346 comes from the register external to system 100 and is controlled by software. Multiplexer 330 selectively outputs strapping signal 378 or SW_CPU_RESET signal 380 as signal 334 under control of strapping override signal 362. In other words, multiplexer 330 initially outputs strapping signal 378 as signal 334. However, after initialization override system 110 controls multiplexer 330 so that it overrides strapping signal 378 and outputs SW_CPU_RESET 380 as signal 334 to multiplexer 340.
Multiplexer 340 receives signal 324 at its control terminal and a HIGH signal 379 (e.g., a “1”) and signal 334 at its input terminals. Multiplexer 340 outputs a signal 344 to OR gate 342. More particularly, the initialization signal 324 selectively control multiplexer 340 to output either HIGH signal 379 or signal 334 as signal 344. OR gate 342 receives signal 344 and an M_BIST_TM signal 384 (e.g., a test control signal). The M_BIST_TM signal 384 is for test processes, as described below. OR gate 342 outputs a signal 346 (e.g., O_CPU_RESET) to device 102 and override system 110.
It is to be appreciated that in the embodiment shown and discussed, OR gate 342 is being used to place the output signal 346 in a certain state in a certain test mode. For example, creating O_CPU_RESET 346. In alternative embodiments, when no test mode is desired, strap value 378 could be used as signal 346 and OR gate 342 would be removed from the system 100.
Override system 110 includes an exclusive OR gate 350, an AND gate 352, and OR gate 354, and a flip-flop 356. Exclusive OR gate 350 receives input signals 346 and SW_CPU_RESET signal 380 (also received by multiplexer 330), and outputs a signal 358. AND gate 352 receives input signals 358 and WR_CPU_RESET_REG 386 and outputs signal 360. WR_CPU_RESET_REG 386 indicates that a SW_CPU_RESET register is being written, which can be a decode of a write signal and an address. WR_CPU_RESET_REG 386 is asserted during a write to the cpu reset register. OR gate 354 receives input signals 360 and 362 (from flip-flop 356, discussed below), and outputs signal 364. Flip-flop 356 receives the HW_RESET_signal 382 (also received by OR gate 322) at its reset terminal, a clock signal CLK, and signal 364. As discussed above, flip-flop 356 outputs signal 362 to OR gate 354 and control system 108.
Operation of the System
In the embodiment shown above, a reset signal 346 for the CPU is being controlled. Initially, when the system or the chip power up, to ensure stable operation of device 102, the reset signal 346 is momentarily brought HIGH until reset assertion. With the assertion of reset the product straps in one way, the O_CPU_RESET 346 will be asserted by default. If the product straps the other way, the O_CPU_RESET 346 will be de-asserted by default. The polarity of O_CPU_RESET 346 determined by the strapping will remain until a register write to SW_CPU_RESET with a value different than the current status of O_CPU_RESET 346 to change the state of the signal. Once the O_CPU_RESET 346 is changed by the register write, subsequent writes will modify the status of O_CPU_RESET 346 based on the value of SW_CPU_RESET.
It is to be appreciated that in alternative embodiments where a product only requires a strapping bit 378 that can be overriden by a register, system 104 and multiplexer 340 and OR gate 342 of system 108 can be removed from the product. Signal 346 can initially take on the value of strapping signal 378.
The behavior of the embodiment shown above can be described in seven time periods (assuming the system is not in MBIST mode and thus m_bist_tm signal 384 is low). A first time period is during power-up reset. In this time period, POWER_UP_RESET_370 is low, 324 is low and 346 takes on a value of signal 379, which is a HIGH.
A second time period is after power-up reset and before regular hardware reset. In this time period, POWER_UP_RESET_370 is HIGH, 324 is LOW, and O_CPU_RESET 346 remains HIGH.
A third time period is during hardware reset. In this time period, HW_RESET_382 is LOW, 376 is HIGH, 324 is HIGH (after a rising edge of CLK 374). Since 324 is HIGH, multiplexer 340 switches over to select input terminal 1, which is signal 379. Signal 382 (in override system 110) is also LOW, so 362 is LOW, and 379 comes from 378 (which is the strap value, e.g. HIGH), 379 is HIGH, 344 is HIGH, and 346 is HIGH.
A fourth time period is after hardware reset is de-asserted. WR_CPU_RESET_REG386 is LOW (because the register is not currently being written to), so 360 is LOW. 362 was LOW and stays LOW (because 364 is LOW). Signal 379 still comes from 378 and 346 remains at the strap value 378 (e.g., HIGH).
A fifth time period lasts for one clock and it's the time when the SW_CPU_RESET register is being written. WR_CPU_RESET_REG 386 is HIGH, allowing 358 to become significant. Assuming that the SW_CPU_RESET register is being written to change the state (i.e., 380 is the opposite state of 346, e.g., LOW) then 358 is HIGH, 360 is HIGH, 364 is HIGH.
A sixth time period starts one clock after the fifth time period. The HIGH value on 364 gets clocked into 356 and appears on 362. Since 362 feeds back around into 354, 364 and 362 will be HIGH from now on. Since 362 and 324 are HIGH, O_CPU_RESET 346 now comes from the sw_cpu_reset register (e.g., 346 is LOW). Depending on clock domains and clock synchronization between the clock for SW_CPU_RESET register and the clock for flip-flop 356, the fifth and sixth time period can be combined into one time period.
A seventh time period occurs after the sw_cpu_reset register has been written to again. Assuming that sw_cpu_reset register is being written to change the state of O_CPU_RESET from LOW back to HIGH, then 380 is HIGH, 362 is HIGH (because it will always be HIGH after the first write), 379 is HIGH, 324 is HIGH, 344 is HIGH, and O_CPU_RESET 346 reflects the current value of the SW_CPU_RESET register, which is a HIGH. Subsequent writes to the sw_cpu_reset register will continue to change the value of O_CPU_RESET 246, while 362 and 324 remain unchanged HIGH.
Therefore, after initialization, system 100 can change into the second state or mode with just a single write. System 100 can also change back to the original state or mode with just a single write. In the embodiment shown above, after an initial write to SW_CPU_RESET 380 that changes the state of signal 346, the status of O_CPU_RESET 346 is determined by the value of SW_CPU_RESET. WR_CPU_RESET_REG 386 is the write pulse that occurs (i.e., goes HIGH) every time SW_CPU_RESET 380 gets programmed. Following the first mode or state, three operations can occur
During a first operation, SW_CPU_RESET 380 is HIGH. Since signal 346 is already HIGH, writing a HIGH to SW_CPU_RESET 380 will not change the state of signal 362 and signal 346 will remain HIGH.
During a second operation, SW_CPU_RESET 380 is LOW. Since signal 346 is already HIGH, writing a LOW to SW_CPU_RESET 380 will change the state of signal 362 to a HIGH and multiplexer 330 will select data from input terminal 1. The input data from input terminal 1 is SW_CPU_RESET 380, which is LOW, thus resulting in signals 334, 344, and 346 being LOW.
During a third operation, signal 346 can be changed back to its initial state or mode by simply writing to SW_CPU_RESET 380 with a HIGH. Since the output signal 346 from module 108 is gated with the SW_CPU_RESET 380 signal by an exclusive-OR 350, only programming SW_CPU_RESET 380 with different polarity as that of signal 346 will change that state of signal 346. Programming SW_CPU_RESET 380 with the same polarity as that of signal 346 will not change the state of signal 346.
Thus, override system 110 can be used to override a current state or mode of device 102 based on receiving specific SW_CPU_RESET and W_CPU_RESET signals from the software running in the product. Having the ability to override strapping signal 378 using override system 110 makes system 100 more versatile (e.g., it can change modes to increase an amount of functions device 102 can perform).
While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
