Abstract:
A circuit, designed for supporting a computer system having a CPU, a monitor, and a system memory electrically connected to the CPU, includes a south bridge, and a north bridge electrically connected to the south bridge, the CPU, and the monitor. The north bridge includes a state machine and a graphics data buffer. When detecting that graphics data transferred by the graphics data buffer to the monitor is insufficient, the state machine sends a north bridge signal to the CPU to access inner data of the system memory.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a chipset, and more particularly, to a method for supporting a monitor to display with a chipset and related computer system. 
   2. Description of the Prior Art 
   Please refer to  FIG. 1 , which is a functional block diagram of a computer system  40  having a K 8  CPU  42  produced by AMD according to the prior art. The computer system  40  further includes a chipset composed of a north bridge  44  and a south bridge  46 , a system memory  18  couples to the CPU  42  directly, a monitor  22  coupled to the north bridge  44  for displaying graphics data, and some peripheral devices, such as a keyboard  24  and a hard disk  26 , coupled to the south bridge  46 . 
   When the CPU  42  processes high speed data logic operations, the CPU  42  is operated in high operating state, such as a power saving state C 0 . However, when the CPU  42  doesn&#39;t process high speed data logic operations, the CPU  42  is operated in power saving states, such C 1 , C 2  or C 3 , to reduce power consumption. 
   When operating in the power saving state C 0 , the CPU  42  is at full speed and capable of receiving and executing instructions. 
   When operating in the power saving state C 1 , the CPU  42  stops receiving instructions to save power consumption. 
   When operating in the power saving state C 2 , the CPU  42  further stops outputting clocks. 
   When operating in the power saving state C 3 , the CPU  42  is unable to support a snoop operation. 
   When the CPU  42  doesn&#39;t operate at full speed, the CPU  42  is switched from the power saving state CO to the power saving state C 3 . When switching CPU Power states, the operating system sends an STPCLK signal through the south bridge  46  to the CPU  42 . After the CPU  42  is ready to be switched, the south bridge  46  sends an asserted LDTSTOP# (‘#’ means low voltage enabled) signal to the north bridge  44  and CPU  42 . Then the CPU  42  enters the power saving state C 3 , and the north bridge  44  disconnects to the CPU  42 . As a result, the snoop operation cannot be performed between the north bridge  44  and the CPU  42 . 
   When the south bridge  46  receives a bus master signal or an interrupt, power states of the CPU  42  has to be switched from a deeper power saving state (for example C 3 ) to a shallower power saving state (for example C 2  to C 0 ). Thus the south bridge  46  sends de-asserted LDTSTOP# signal to the north bridge  44  and CPU  42  for entering the CPU  42  into a shallower power saving state and reconnecting the north bridge  44  and the CPU  42 . Therefore, the bus master signal and the interrupt can function normally. 
   Since the monitor  22  has to display graphics data continuously and the data must be access form the system memory  18  through the CPU  42 . When the south bridge  46  sends the asserted LDTSTOP# signal to disconnect the north bridge  44  and the CPU  42 , whether the graphics data stored in a buffer of the north bridge  44  is sufficient is not controllable. Therefore, if the graphics data stored in the buffer is not sufficient, the CPU  42  has to be switched to operate in a shallower power saving state, and then more graphics data can be acquired from the system memory  18 . If the time it takes for the CPU  42  to be switched to operate from the power saving state C 3  to the power state C 0  is long, and the CPU  42  cannot acquire enough graphics data in time, the monitor  22  encounters a display interruption problem. 
   Taking the example of switching power state from a deeper power saving state to the power saving state C 0 , when the north bridge  44  determines that the graphics data stored in the buffer is not sufficient for the monitor  22  to display, the north bridge  44  sends an AGP BUSY signal to the south bridge  46 . Then, the south bridge  46  sends the de-asserted LDTSTOP# to the north bridge  44  and the CPU  42  for switching the CPU  42  to a shallower power saving state and reconnecting the north bridge  44  and the CPU  42 , and then performing graphics data access from the system memory  18 . 
   However the time consumption of the above mention steps, from sending signals to completing confirmation, is longer than that the time for the buffer in the north bridge  44  to output graphics data. This problem is more serious especially in a graphic integrated chipset due to the complicated inner circuit without having enough space for data storage. 
   SUMMARY OF THE INVENTION 
   The invention provides a chipset for overcoming the above-mentioned problems. 
   If the north bridge have insufficient graphics data in the buffer, the chipset can still access graphics data stored in the system memory without switching the power saving state of the CPU. 
   The chipset includes a south bridge, a north bridge coupled to the south bridge, a CPU and a monitor of a computer system. The CPU has at least a deep power saving state and at least a shallow power saving state. The computer system further includes a system memory. The north bridge has a state machine coupled to the CPU, and a graphics data buffer coupled to the state machine and the monitor, wherein when the CPU is in the deep power saving state and the state machine detects that graphics data transferred from the graphics data buffer to the monitor is insufficient, the state machine sends an NB control signal to the CPU to access inner data stored in the system memory. 
   A computer system includes: a system memory for storing an inner data; a CPU couples to the system memory, wherein the CPU having at least a shallow power saving state and a deep power saving state; a monitor; and a chipset couples to the CPU and the monitor. When the CPU is in the deep power saving state, if the graphics data stored in chipset is insufficient, the chipset sends an NB control signal to the CPU to access inner data stored in the system memory. 
   A method supports a monitor of a computer system with a chipset. The computer system has a CPU and a system memory coupled to the CPU, the CPU having at least a shallow power saving state and a deep power saving state. The method includes: sending an NB control signal to the CPU when the CPU is in the deep power saving state and graphics data transferred to the monitor is insufficient, and the CPU switching to access inner data stored in the system memory to provide the graphics data. 
   These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a functional block diagram of a computer system having a K 8  CPU produced by AMD according to the prior art. 
       FIG. 2  is a functional block diagram of a computer system having a K 8  CPU of the preferred embodiment according to the present invention. 
       FIG. 3  is a waveform diagram of inner control signals for switching a shallow power saving state into a deep power saving state of the prior art and the present invention. 
       FIG. 4  is a circuit diagram of a state machine of the computer system shown in  FIG. 2 . 
       FIG. 5  is a truth table of signals shown in  FIG. 4 . 
   

   DETAILED DESCRIPTION 
   Please refer to  FIG. 2 , which is a functional block diagram of a computer system  70  having a K 8  CPU  62  produced by AMD of the preferred embodiment according to the present invention. 
   The computer system  70  further includes a chipset having a south bridge  76  and a north bridge  74 , a system memory  68  coupled to the CPU  62  directly, and a monitor  64  couples to the north bridge  74  for displaying graphics data. The north bridge  74  has a state machine  78  and a graphics data (GFX) buffer  80 . 
   Since only the north bridge  74  knows whether or not the monitor  64  has sufficient graphics data to display, the present invention provides a state machine  78  within the north bridge  74  to monitor the graphics data stored in the GFX buffer  80 . By using an NB control signal (which will be called LDTSTOP_NB# hereafter) sent from the state machine  78  to the CPU  62 , the CPU  62  can only enable an embedded memory controller without enabling the logic operation Therefore the north bridge  74  can still access the graphics data stored in the system memory  68  directly even if the CPU  62  still stays in the original power saving state. 
     FIG. 3  is a timing diagram of switching the power state from a shallower power saving state to a deeper power saving state of the prior art and the present invention. 
   When the south bridge  76  receives an asserted signal from the CPU  62 , the CPU  62  is switched from C 0  to C 3 . Then an LDTSTOP_SB# signal, similar to the asserted LDTSTOP# signal, is transmitted to the north bridge  74 , as shown in region  98  shown in  FIG. 3 . After receiving the LDTSTOP_SB#, the north bridge  74  checks a data display status of the monitor  64 , and then sends an asserted LDTSTOP_NB# signal to the CPU  62  to disconnect the north bridge  74  and the CPU  62  only when data (which will be acquired by an internal GFX during  100  shown in  FIG. 3 ) stored in the GFX buffer  80  is still sufficient for the monitor  64  to display. Since the north bridge  74  transfers data to the GFX buffer  80  by down counting method, the problem resulting from a system slowly switching power saving states and having insufficient data to display will not occur. 
   Moreover, if the CPU  62  is operated in a deeper power saving state (ex. C 3 ), if the graphics data stored in the GFX buffer  80  is not enough for the monitor  64  to display, the state machine  78  in the north bridge  74  sends a de-asserted LDTSTOP_NB# signal, which is a non-snoop signal and is shown in  FIG. 3  in region  104 , to control the memory controller of the CPU  62  to switch to the function of accessing the system memory  68  without changing the LDTSTOP_SB# asserted state. Therefore, the power saving state of the CPU  62  doesn&#39;t change, and the data stored in the system memory  68  can be accessed to provide for the GFX buffer  80  during region  104  shown in  FIG. 3 . Comparing to a region  96  of the LDTSTOP# signal shown in  FIG. 3  which shows that the prior art cannot access the system memory  68  without generating a de-asserted LDTSTOP# and switching the CPU  62  to the shallower power saving state C 0 . Therefore the present invention is faster and saves more power. 
   Please refer to  FIG. 4 , which is a circuit diagram of the state machine  78 . 
   The state machine  78  includes a first multiplexer  82 , a second multiplexer  84 , and a D-type flip-flop  86 . The first multiplexer  82  transfers either the LDTSTOP_SB# or a state signal GFX from the GFX buffer  80  to the second multiplexer  84  according to the state signal GFX. 
   For example, if the state of the state signal GFX is “ 0 ” (representing that the data stored in the GFX buffer  80  are enough for the monitor  64  to display), the first multiplexer  82  selects the LDTSTOP_SB# outputting to the second multiplexer  84 . On the contrary, if the data stored in the GFX buffer  80  are not sufficient (the state signal GFX is “1”), the first multiplexer  82  selects the state signal GFX (labeled as “1” in  FIG. 4 ) outputting to the second multiplexer  84  for enabling the LDTSTOP_NB(t)# signal, which is outputted from the D-type flip-flop  86 , to be “1” as shown in  FIG. 3  as region  100 . When the data stored in the GFX buffer  80  is sufficient, the state of the state signal GFX is “0”, and the first multiplexer  82  outputs the LDTSTOP_SB# signal for enabling the LDTSTOP_NB(t)# signal to be “0”, as shown in  FIG. 3  as region  102 . 
   The second multiplexer  84  is controlled by a down counter (not shown in  FIG. 3 , the down counter can be integrated into the state machine  78 ) of the north bridge  74 . When the down counter is not yet counting to zero, an assert/de-assert signal is used to control an input end, which has an output equals to “0”, for outputting an NB−1 control signal. The NB−1 control signal is generated according to feedback of LDTSTOP_NB(t)# from an output end Q of the D-type flip-flop  86  and is inputted to the input end D of the D-type flip-flop  86  via the second multiplexer  84 . Thus, if the down counter is not yet counting to zero, state of LDTSTOP_NB(t)# will keep at the state of the previous LDTSTOP_NB(t)# (called an LDTSTOP NB(t−1)# hereafter), thus the switching is performed after a predetermined period of time. 
   As shown in  FIG. 3 , the interval between  102  and  104  is not less than a predetermined period (for example one microsecond). During the predetermined period, the north bridge  74  will not change LDTSTOP_NB#, which is transferred to the CPU  62 . On the contrary, when the down counter is counting to zero, the second multiplexer  84  using an assert/de-assert signal to control the input end, which has the output equals to “1”, for outputting LDTSTOP_SB# from an output end O 1  of the first multiplexer  82  or the state signal GFX of the GFX buffer  80  to the input end D of the D-type flip-flop  86 . 
   The operation of the state machine  78  for generating the LDTSTOP_NB(t) is described as follows. 
   Please refer to  FIG. 5 , which is a truth table of the state signal GFX, the assert/de-assert signal, LDTSTOP_SB#, LDTSTOP_NB(t−1)# and LDTSTOP_NB(t)#. When the down counter is not yet counting to zero (the assert/de-assert is “0”), the duration of the LDTSTOP_NB(t)# is less than one microsecond (or less than a programmable shortest period). The computer system  70  does not allow LDTSTOP_NB(t)#, from the north bridge  74  to the CPU  62 , to switch, so the state of LDTSTOP_NB(t)# is keeps to the state of LDTSTOP_NB(t−1)# (as L 1 -L 4  and L 9 -L 12  in the table show). 
   When the down counter is counting to zero (the assert/de-assert shown in  FIG. 5  is “1”), if the state signal GFX is equal to “0” (the first multiplexer  82  shown in  FIG. 4  transfers LDTSTOP_SB# to the second multiplexer  84 ), the north bridge  74  generates succeeding LDTSTOP_NB(t)# according to LDTSTOP_SB#, as L 5 -L 8  in the table shows, without taking into consideration the state of LDTSTOP_NB(t−1). 
   When the down counter is counting to zero, and the state of state signal GFX is equal to “1” (the first multiplexer  82  outputs the state signal GFX, which state is equal to “1”, to the second multiplexer  84 ), the following generating LDTSTOP_NB(t) of the north bridge  74  is generated to ensure the north bridge  74  still can accessing the system memory  68 . So that, the internal GFX can access data ready to be displayed on the monitor  64  from the system memory  68  through the CPU  62  and the north bridge  74 . In  FIG. 5 , this is shown as LDTSTOP_NB(t) values equal to “1” in L 12 -L 16 . 
   Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.