Motorola MSC8101 ADS User's Guide download pdf (Page 38)

1-14 MSC8101 User’s Guide

MSC8101 Overview

BD.bd_cstat.bit

The structural elements of a buffer descriptor are defined as follows:

■ Status and control. The 16-bit value at offset+0x0, which contains status and

control bits that control and report status information on the data transfer. The CPM

updates the status bits after the buffer is sent or received. Only this field differs for

each protocol. Refer to the MSC8101 Reference Manual for each protocol’s

RxBD.bd_cstat and TxBD.bd_cstat bit description.

■ Data length. The 16-bit value at offset+0x2, which contains the number of bytes

sent or received.

■ RxBD data length. The number of bytes the CP writes into the RxBD buffer once

the BD closes. The communications processor (CP) updates this field after the

received data is placed into the buffer and the buffer is closed. You do not need to

initialize this field. In frame-based protocols, except for the SCC transparent mode,

RxBD.bd_length contains the total frame length including CRC bytes. If a

received frame’s length, including CRC, is an exact multiple of the parameter

RAM maximum receive buffer length MRBLR, the last buffer holds no actual data

but the associated BD contains the total frame length.

■ TxBD data length. The number of data bytes the controller needs to transmit from

its buffer. The CP never modifies this field, which is initialized by the user.

■ Buffer pointer. The 32-bit data at offset+0x4, which points to the beginning of

the buffer in internal or external memory.

■ RxBD buffer pointer. The buffer pointer value must be a multiple of four to be

word-aligned.

■ TxBD buffer pointer. The buffer pointer value can be even or odd.

1.3.7.4 Parameter RAM

In the dual-port RAM memory map (see Table 1-4), Banks 9–10

(

IMM+$8000:IMM+$8FFF) store parameters associated with the SCCs, FCCs, MCCs,

SMCs, SPI, and I

C controllers. The parameter RAM contains parameters for operating

Table 1-3. Buffer Descriptor Naming Conventions

BD Field Example

RxBD/TxBD bd_cstat TxBD.bd_cstat. R refers to the ready bit in the TxBD’s status and

control field. Refer to the

MSC8101 Reference Manual

for the

protocol’s status and control field bit definition.

bd_length RxBD.bd_length refers to RxBD’s data length field.

bd_addr RxBD.bd_addr refers to RxBD’s buffer pointer field.

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Motorola MSC8101 ADS User's Guide Page 38