Cypress PSoC CY8CTMG20 Series, Technical Reference Manual

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166 PSoC CY8CTMG20x and CY8CTST200 TRM, Document No. 001-53603 Rev. *C
Full-Speed USB
20.2.2 USB SRAM
The PSoC USB System Resource contains dedicated 512
bytes SRAM. This SRAM is identical to 2 SRAM pages used
in the PSoC Core; however, it is not accessible by way of the
M8C memory access instructions. The USB's dedicated
SRAM may only be accessed by way of the PMA registers.
For more information on how to use the USB's dedicated
SRAM, see the next section, PSoC Memory Arbiter (PMA).
The USB SRAM contents are not directly affected by any
reset, but must be treated as unknown after any POR, WDR,
and XRES.
20.2.2.1 PSoC Memory Arbiter
The PSoC Memory Arbiter (PMA) is the interface between
the USB's dedicated SRAM and the two blocks that access
the SRAM: the M8C and the USB SIE. The PMA provides
16 channels to manage data with four Endpoints/8 channels
mapped to Page 0 of USB dedicated SRAM and other four
Endpoints/8 channels mapped to Page 1 of USB dedicated
SRAM. All of the channel registers may be used by the
M8C, but the eight non-control USB endpoints are each allo-
cated to a specific set of PMA channel registers. It is the
responsibility of the firmware to ensure that the M8C is not
accessing a set of channel registers that are in use by the
USB SIE.
If the M8C wants to access the same data that an SIE chan-
nel is using, two channels must be configured to access the
same SRAM address ranges.
Table 20-2 shows the map-
ping between PMA channels and which blocks can use
them.
Table 20-1. Mode Encoding for Control and Non-Control Endpoints
Mode Encoding SETUP IN OUT Comments
Disable 0000 Ignore Ignore Ignore Ignore all USB traffic to this endpoint.
NAK IN/OUT 0001 Accept NAK NAK NAK IN and OUT token.
Status OUT Only 0010 Accept STALL Check For control endpoint, STALL IN and ACK zero byte OUT.
STALL IN/OUT 0011 Accept STALL STALL For control endpoint, STALL IN and OUT token.
Reserved 0100 Ignore Ignore Ignore
ISO OUT 0101 Ignore Ignore Always Isochronous OUT.
Status IN Only 0110 Accept TX 0 Byte STALL For control endpoint, STALL OUT and send zero byte data for IN token.
ISO IN 0111 Ignore TX Count Ignore Isochronous IN.
NAK OUT 1000 Ignore Ignore NAK Send NAK handshake to OUT token.
ACK OUT (STALL = 0) 1001 Ignore Ignore ACK
This mode is changed by the SIE to mode 1000 on issuance of ACK hand-
shake to an OUT.
ACK OUT (STALL = 1) 1001 Ignore Ignore STALL STALL the OUT transfer.
Reserved 1010 Ignore Ignore Ignore
ACK OUT – STATUS
IN
1011 Accept TX0 Byte ACK ACK the OUT token or send zero byte data for IN token.
NAK IN 1100 Ignore NAK Ignore Send NAK handshake for IN token.
ACK IN (STALL = 0) 1101 Ignore TX Count Ignore
This mode is changed by the SIE to mode 1100 after receiving ACK hand-
shake to an IN data.
ACK IN (STALL = 1) 1101 Ignore STALL Ignore STALL the IN transfer.
Reserved 1110 Ignore Ignore Ignore
ACK IN – Status OUT 1111 Accept TX Count Check Respond to IN data or Status OUT.
Table 20-2. PMA Channel Assignments
PMA
Channel
USB SIE M8C Channel Registers (PMAx_xx)
0 Page 0 PMA0_DR, PMA0_RA, PMA0_WA
1 EP1 Page 0 PMA1_DR, PMA1_RA, PMA1_WA
2 EP2 Page 0 PMA2_DR, PMA2_RA, PMA2_WA
3 EP3 Page 0 PMA3_DR, PMA3_RA, PMA3_WA
4 EP4 Page 0 PMA4_DR, PMA4_RA, PMA4_WA
5 Page 0 PMA5_DR, PMA5_RA, PMA5_WA
6 Page 0 PMA6_DR, PMA6_RA, PMA6_WA
7 Page 0 PMA7_DR, PMA7_RA, PMA7_WA
8 Page 1 PMA8_DR, PMA8_RA, PMA8_WA
9 EP5 Page 1 PMA9_DR, PMA9_RA, PMA9_WA
10 EP6 Page 1 PMA10_DR, PMA10_RA, PMA10_WA
11 EP7 Page 1 PMA11_DR, PMA11_RA, PMA11_WA
12 EP8 Page 1 PMA12_DR, PMA12_RA, PMA12_WA
13 Page 1 PMA13_DR, PMA13_RA, PMA13_WA
14 Page 1 PMA14_DR, PMA14_RA, PMA14_WA
15 Page 1 PMA15_DR, PMA15_RA, PMA15_WA
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