NXP Semiconductors LPC43 Series User Manual

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NXP Semiconductors LPC43 Series User Manual Manual pdf 676 page image

UM10503 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2012. All rights reserved.User manual Rev. 1.3 — 6 July 2012 676 of 1269NXP Semiconductors UM10503Chapter 25: LPC43xx USB APIMSC_Read void(*void(* USBD_MSC_INIT_PARAM::MSC_Read)(uint32_t offset, uint8_t **dst, uint32_t length))(uint32_toffset, uint8_t **dst, uint32_t length)MSC Read callback function.This function is provided by the application software. This function gets called when hostsends a read command.Parameters:1. offset = Source start address.2. dst = Pointer to a pointer to the source of data. The MSC function drivers implemented instack are written with zero-copy model. Meaning the stack doesn't make an extra copy ofbuffer before writing/reading data from USB hardware FIFO. Hence the parameter ispointer to a pointer containing address buffer (uint8_t** dst). So that the user applicationcan update the buffer pointer instead of copying data to address pointed by theparameter. /note The updated buffer address should be accessible by USB DMA master.If user doesn't want to use zero-copy model, then the user should copy data to theaddress pointed by the passed buffer pointer parameter and shouldn't change theaddress value. See Zero-Copy Data Transfer model for more details on zero-copyconcept.3. length = Number of bytes to be read.Returns:Nothing.Table 528. USBD_MSC_INIT_PARAM class structureMember Description