Nec Network Controller uPD98502 Bedienungsanleitung PDF herunterladen (Seite 333)

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CHAPTER 6 USB CONTROLLER

Preliminary User’s Manual S15543EJ1V0UM

333

Figure 6-3. Mailbox Configuration

31 0

U_TMSA(U_RMSA)

U_TMWA(U_RMWA)

U_TMBA(U_RMBA)

U_TMRA(U_RMRA)

When USB Controller writes an indication, the write pointer (U_TMWA or U_RMWA) is incremented. Every time

that USB Controller writes an indication, it also sets the transmit/receive finish bit of the corresponding EndPoint and,

issues an interrupt if it is not masked.

The write pointer is forced to jump to the start address (U_TMSA or U_RMSA) when it reaches the bottom address

(U_TMBA or U_RMBA). USB Controller uses the read pointer (U_TMRA or U_RMRA) to prevent the overwriting of

those indications that the V

4120A has not yet read out. The read pointer (U_TMRA or U_RMRA) is managed by the

4120A. Each time the V

4120A reads an indication from a MailBox, it writes the address to be read next time into

the read pointer register (U_TMRA or U_RMRA).

When both the write pointer (U_TMWA or U_RMWA) and read pointer (U_TMRA or U_RMRA) point to the same

address, USB Controller sets the TMF bit (transmit MailBox full) or RMF bit (receive MailBox full) of the USB General

Status Register 1 to indicate the MailBox full state and issues an interrupt if it is not masked.

In the MailBox full status, USB Controller will not issue the next indication. The V

4120A must read an indication

from the full MailBox and update the read pointer (U_TMRA or U_RMRA).

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