What does AGP stand for?
Video cards with a TV output connection are capable of displaying a computer's video on a television. It is responsible for making the decisions for processing the video card's graphical input and output data. For every cycle that PIPE is asserted, the card sends another request without waiting for acknowledgement from the motherboard, up to the configured maximum queue depth.
Video cards, like the one shown above, simply plug into an AGP slot and connect a monitor or other video display device to a computer. The photo below shows what an AGP slot looks like. For each cycle when the GNT is asserted and the status bits have the value 00p, a read response of the indicated priority is scheduled to be returned.
The command and high-order bits are as previously specified. If the response is longer than that, both the card and motherboard must indicate their ability to continue on the third cycle by asserting IRDY initiator ready and TRDYrespectively. Odd-numbered A-side contacts, and even-numbered B-side contacts are in the lower row 1. It is hidden under a fan and heatsink in the first picture to keep it cool so that it doesn't agp slot stands for.
At the next available opportunity typically the next clock cyclethe card will assert IRDY initiator ready and begin transferring the data portion of the oldest request in the indicated write queue. The others are in the upper row 3.
This is the same as a read request, but the length is multiplied by four. For each cycle when GNT is asserted and agp slot stands for status bits have the value 01p, write data is scheduled to be sent across the bus. This operates like a regular PCI dual address cycle; it is accompanied by the low-order 32 bits of the address and the lengthand the following cycle includes the high 32 address bits and the desired command.
This does not queue a request, but sets values that will be used in all future queued requests. Dual address cycle When making a request to an address abovethis is used to indicate that a second address cycle will follow with additional address bits. AGP responses[ edit ] While asserting GNTthe motherboard may instead indicate via the ST bits that a data phase for a queued request will be performed next.
It transfers data at MBs per second. Below is a picture of three PCI Express slots. PCIe x16 slots are used for video cards. It transfers data at 2. The "DVI Out" connector shown in picture above connects to a digital video display.
Instead, requests are broken into bit pieces which are sent as two bytes across the SBA bus. Flush Force previously written data to memory, for synchronization. You must be careful to match the card and slot with the correct mode. At the next available opportunity typically the next clock cyclethe motherboard will assert TRDY target ready and begin transferring the response to the oldest request in the indicated read queue.
Only returning 1 agp slot stands for forbidden, as writes must complete before following reads. Unlike reads, there is no provision for the card to delay the write; if it didn't have the data ready to send, it shouldn't have queued the request. This acts as a low-priority read, taking a queue slot and returning 8 bytes of random data to indicate completion.
Sideband addressing has the advantage that it mostly eliminates the need for turnaround cycles on the AD bus between transfers, in the usual case when read operations greatly outnumber writes. If the address is 64 bits, a dual address cycle similar to PCI is used. AGP 2x mode transfers data at MBs per second. The AGP card and the monitor are what determine the quality of a computer's video display.
AGP 1x mode is the oldest. Obviously, the motherboard will attempt to complete high-priority requests first, but there is no limit on the number of low-priority responses which may be delivered while the high-priority request is processed. Some cards and slots are capable of running in more than one mode. Ordinarily, for increased performance, AGP uses a very weak consistency modeland allows a later write to pass an earlier read.
The address and length supplied with this command are ignored. It also mandated side-band addressing, thus dropping the dual address cycle, leaving only four request types: AGP 4x mode transfers data at 1. The photo above shows what a GPU looks like. AGP slots and cards come in 4 different modes. Bit R is reserved. The two cycles make one request, and take only one slot in the request queue.
The card may also assert the RBF read buffer full signal to indicate that it is temporarily unable to receive more low-priority read responses. The possible values are: The connector has 66 contacts on each side, although 4 are removed for each keying notch. Any number of requests may be queued by sending only this pattern, as long as the command and higher address bits remain the same.
The video card is in charge of controlling the video display. And the signal is re-used for another purpose in the AGP 3. Accelerated Graphics Port connector pinout :