Posted on August 12, 2014 at 20:08
Hi GPTechinno,
> We are very interested to know if you managed to write your own USB Printer Class ? > We are trying to do so based on STM32Cube
As ST’s staff said in above post, you may start with one of existing host class driver implementation, like MSC (Mass-Storage Class). But surely, just showing a starting point isn’t helpful answer ;) You’ll need some guidance, how to modify the implementation.
Here is brief outline of modification, based on STM32Cube_FW_F4_V1.3.0
0) Start with
- \STM32Cube_FW_F4_V1.3.0\Projects\STM324xG_EVAL\Applications\USB_Host\MSC_Standalone\Src\main.c
- \STM32Cube_FW_F4_V1.3.0\Middlewares\ST\STM32_USB_Host_Library\Class\MSC\Src\usbh_msc.c
1) make Class driver object (structure instance), and register it
usbh_msc.c defines this class driver structure
usbh_msc.c
USBH_ClassTypeDef USBH_msc =
{
''MSC'',
USB_MSC_CLASS,
USBH_MSC_InterfaceInit,
USBH_MSC_InterfaceDeInit,
USBH_MSC_ClassRequest,
USBH_MSC_Process,
USBH_MSC_SOFProcess,
NULL,
};
usbh_msc.h
/* MSC Class Codes */
#define USB_MSC_CLASS 0x08
extern USBH_ClassTypeDef USBH_msc;
#define USBH_MSC_CLASS &USBH_msc
This structure is modified for printer class, by replacing ''MSC'' to ''PRN'', like
#define USB_PRN_CLASS 0x07
extern USBH_ClassTypeDef USBH_prn;
#define USBH_PRN_CLASS &USBH_prn
USBH_ClassTypeDef USBH_prn =
{
''MSC'',
USB_PRN_CLASS,
USBH_PRN_InterfaceInit,
USBH_PRN_InterfaceDeInit,
USBH_PRN_ClassRequest,
USBH_PRN_Process,
USBH_PRN_SOFProcess,
NULL,
};
main.c registers this class driver object.
main.c
int main(void)
{
...
/* Add Supported Class */
//USBH_RegisterClass(&hUSBHost, USBH_MSC_CLASS);
USBH_RegisterClass(&hUSBHost, USBH_PRN_CLASS);
2) code class driver routines
2-1) USBH_PRN_InterfaceInit() <- USBH_MSC_InterfaceInit()
This routine find printer interface on the descriptor set using USBH_FindInterface()
//interface = USBH_FindInterface(phost, phost->pActiveClass->ClassCode, MSC_TRANSPARENT, MSC_BOT);
#define PRN_PRINTERS 0x01 // sub-class
#define PRN_UNIDIRECTIONAL 0x01 // protocols
#define PRN_BIDIRECTIONAL 0x02
#define PRN_1284_4 0x03
#define PRN_VENDOR 0xFF
interface = USBH_FindInterface(phost, phost->pActiveClass->ClassCode, PRN_PRINTERS, PRN_BIDIRECTIONAL);
Your target printer may have other class-protocol value than PRN_BIDIRECTIONAL.
Find it using a utility, like USBView
http://www.ftdichip.com/Support/Utilities/usbview.zip
The rest of code lines are (almost) usable as is, except
- replace every ''MSC'' into ''PRN'' on the variable names
- you don’t need these MSC-specific code lines in this routine.
MSC_Handle->current_lun = 0;
MSC_Handle->rw_lun = 0;
USBH_MSC_BOT_Init(phost);
/* De-Initialize LUNs information */
USBH_memset(MSC_Handle->unit, 0, sizeof(MSC_Handle->unit));
2-2) USBH_PRN_InterfaceDeInit() <- USBH_MSC_InterfaceDeInit()
No change required.
2-3) USBH_PRN_ClassRequest() <- USBH_MSC_ClassRequest()
In the code lines under ''case MSC_REQ_GET_MAX_LUN:'', the original puts Get_Max_Lun request to the target USB stick. Instead, GET_DEVICE_ID request is put to the printer.
By GET_DEVICE_ID request, the printer returns DEVICE_ID string, which holds supported PDLs (Page Description Language) after ''CMD:'' tag. You need a ''PCL'' printer, as you said your other post. Confirm the printer should support one of ''PCL'' protocols.
For DEVICE_ID string, refer to this port.
http://www.keil.com/forum/57021/
2-4) USBH_PRN_Process() <- USBH_MSC_Process()
This routine is repeatedly called by the main loop, by USBH_Process(), to run the class.
The original code is fully MSC-specific. Then rewrite entire code lines.
For printer class, the printer status (paper empty, on-line, error) is retrieved by GET_PORT_STATUS request
2-5) The PCL data is sent to the printer over the bulk OUT endpoint, using USBH_BulkSendData(PRN_Handle->OutPipe)
The completion of transfer is detected by polling USBH_LL_GetURBState(), until it returns USBH_URB_DONE.
Tsuneo
