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Subsections


Microprocessor/USB controller

All slow-control interaction between the user and the SURF board happens through the USB controller. Our USB controller chip (a Cypress EZ-USB AN2131) is a combination of USB line driver, RAM, souped-up 8051 microprocessor and i2c controller.

USB interface

The USB controller part of the EZ-USB provides an interface to the SURF board for the machine running the AMBUSH software. It accepts requests to enable or disable the various features of the SURF board; set the settable settings; and read out the status of the board. Tables 3.1 and 3.2 list the requests that the host computer is allowed to make of the SURF board. (The additional requests required by the USB protocol specification are not listed in this here manual.)

Global requests are made through control transfers to the EZ-USB's endpoint EP0. The format of the request is shown in Table 3.3.

Module-specific requests are made through bulk transfers; for the $n$th module (zero-offset), the transfer is made to the $n+1$st endpoint. (This arrangement is necessary because the USB specification requires EP0 to be the control endpoint.) Byte 0 of a module-specific transfer specifies the request (choose from one of those listed in Table 3.2); the remaining 0 to 63 bytes are arguments to the command as specified in Table 3.2. Note that if you ask an endpoint for the status of its module by sending it the SURF_MOD_STATUS request, the next request you make to that endpoint must be a bulk in request so that the endpoint can rid itself of the status information it has generated. Table 3.4 shows the format of the status report.

Table 3.1: Global requests supported by the SURF board USB interface. $m_n = 1$ indicates that the $n$th module is enabled. These requests should be addressed to EP 0.
\begin{table}\centering\begin{tabularx}{\textwidth} {l\vert X\vert l} \hline\hli... ...rature interlocking mechanism& None \\ \hline\hline \end{tabularx}\end{table}



Table 3.2: Module-specific requests supported by the SURF board USB interface. A request to module $n$ (zero-offset) should be addressed to EP $n+1$. See the last paragraph of Sec. 3.6.2 for an explanation of the ``DAC hint'' argument to the SURF_MOD_SET_ANAL/SURF_MOD_SET_DIG request.
\begin{table}\centering\begin{tabularx}{\textwidth} {l\vert X\vert X} \hline\hli... ...erate the module status report. & None\\ \hline\hline \end{tabularx}\end{table}



Table 3.3: Global request format.
\begin{table}\centering\begin{tabularx}{\textwidth} {l\vert X\vert l} \hline\hli... ...rature interlocking mechanism& None \\ \hline\hline \end{tabularx}\end{table}



Table 3.4: Module status report format.
\begin{table}\centering\begin{tabularx}{\textwidth} {l\vert X\vert l} \hline\hli... ...rature interlocking mechanism& None \\ \hline\hline \end{tabularx}\end{table}



Microprocessor I/O

The microprocessor part of the EZ-USB has two eight-bit digital I/O ports and an i2c bus controller. The I/O bits are allocated as follows:

Regulator enable (END and ENA):
Eight bits are used to turn on the eight regulators independently of each other.
Thermal interlock reset (NRESET):
One bit sends a reset signal to the thermal shutdown mechanism; any power supplies in thermal interlock are brought out of thermal interlock.
Thermal shutdown readout (TS):
Each module has a bit that goes high when the thermal interlock engages.
Readout select (NSEL):
Two bits select which module can transmit data back to the TPCC.
Enable single-module control (ES):
The ES bit determines whether the TPCC writes to all modules or only the selected one.
SURF uses the i2c bus controller of the EZ-USB for the following purposes:
EEPROM access:
The SURF board contains a 128-Kb EEPROM. The EEPROM stores the 8051 firmware (see Sec. 3.6.4).
ADC readout:
Two twelve-channel ADCs digitize the module quantities of interest. The twenty-four quantities that the EZ-USB can read are: module temperature \ensuremath{\times} 4; remote-sensed module ground \ensuremath{\times} 4; remote-sensed module VDD \ensuremath{\times} 4; remote-sensed VDDA \ensuremath{\times} 4; analog supply current \ensuremath{\times} 4; and digital supply current \ensuremath{\times} 4.
Regulator control:
The EZ-USB sets the voltage levels of the supply regulators through the AD5242 digital potentiometers in Fig. 3.1.


``Firmware regulation''

In addition to processing the set/get requests from the host computer, the 8051 also optionally corrects for the voltage drop in the module power supply. The firmware continuously digitizes the supply voltages sensed at the modules; it trims the regulator output until the sensed voltage falls within tolerance of the set voltage.


Microprocessor firmware

The controller firmware lives in the jboard/firm directory. To build it you need SDCC, the Small Device C Compiler, from http://sdcc.sourceforge.net. Typing make in the firmware directory will build two files: firm.ee and loader.ihx. The former is the actual firmware, in a format suitable for bootloading from the on-board EEPROM. The latter is loader firmware for the EZ-USB that allows the host computer to write to the EEPROM through the EZ-USB.

To download the firmware into the EEPROM on the SURF board, do the following:

next up previous contents
Next: libsurf Up: Hacking the hardware Previous: Clock return   Contents
Johannes Muelmenstaedt 2004-03-31